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1662-5129162022Frontiers in neuroanatomyFront NeuroanatAn Update on the Molecular Mechanism of the Vertebrate Isthmic Organizer Development in the Context of the Neuromeric Model.82697682697682697610.3389/fnana.2022.826976A crucial event during the development of the central nervous system (CNS) is the early subdivision of the neural tube along its anterior-to-posterior axis to form neuromeres, morphogenetic units separated by transversal constrictions and programed for particular genetic cascades. The narrower portions observed in the developing neural tube are responsible for relevant cellular and molecular processes, such as clonal restrictions, expression of specific regulatory genes, and differential fate specification, as well as inductive activities. In this developmental context, the gradual formation of the midbrain-hindbrain (MH) constriction has been an excellent model to study the specification of two major subdivisions of the CNS containing the mesencephalic and isthmo-cerebellar primordia. This MH boundary is coincident with the common Otx2-(midbrain)/Gbx2-(hindbrain) expressing border. The early interactions between these two pre-specified areas confer positional identities and induce the generation of specific diffusible morphogenes at this interface, in particular FGF8 and WNT1. These signaling pathways are responsible for the gradual histogenetic specifications and cellular identity acquisitions with in the MH domain. This review is focused on the cellular and molecular mechanisms involved in the specification of the midbrain/hindbrain territory and the formation of the isthmic organizer. Emphasis will be placed on the chick/quail chimeric experiments leading to the acquisition of the first fate mapping and experimental data to, in this way, better understand pioneering morphological studies and innovative gain/loss-of-function analysis.Copyright © 2022 Hidalgo-Sánchez, Andreu-Cervera, Villa-Carballar and Echevarria.Hidalgo-SánchezMatíasMDepartamento de Biología Celular, Facultad de Ciencias, Universidad de Extremadura, Badajoz, Spain.Andreu-CerveraAbrahamAInstituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Alicante, Spain.Villa-CarballarSergioSDepartamento de Biología Celular, Facultad de Ciencias, Universidad de Extremadura, Badajoz, Spain.EchevarriaDiegoDInstituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Alicante, Spain.engJournal ArticleReview20220324
SwitzerlandFront Neuroanat1014779431662-5129Fgf8Gbx2Otx2PAXWnt1engrailedhindbrainmidbrain202112120222282022411527202241260202241261202211epublish35401126PMC898713110.3389/fnana.2022.826976Acampora D., Avantaggiato V., Tuorto F., Barone P., Perera M., Choo D., et al. (1999). Differential transcriptional control as the major molecular event in generating Otx1−/− and Otx2−/− divergent phenotypes. Development 126, 1417–1426. 10.1242/dev.126.7.141710.1242/dev.126.7.141710068635Acampora D., Avantaggiato V., Tuorto F., Briata P., Corte G., Simeone A. (1998). Visceral endoderm-restricted translation of Otx1 mediates recovery of Otx2 requirements for specification of anterior neuralplate and normal gastrulation. Development 125, 5091–5104. 10.1242/dev.125.24.509110.1242/dev.125.24.50919811592Acampora D., Avantaggiato V., Tuorto F., Simeone A. (1997). Genetic control of brain morphogenesis through Otx gene dosage requirement. Development 124, 3639–3650. 10.1242/dev.124.18.363910.1242/dev.124.18.36399342056Acampora D., Gulisano M., Broccoli V., Simeone A. (2001). Otx genes in brain morphogenesis. Progr. Neurobiol. 64, 69–95. 10.1016/s0301-0082(00)00042-310.1016/s0301-0082(00)00042-311250063Acampora D., Mazan S., Lallemand Y., Avantaggiato V., Maury M., Simeone A., et al. (1995). Forebrain and midbrain regions are deleted in Otx2−/− mutants due to a defective anterior neuroectoderm specification during gastrulation. Development 121, 3279–3290. 10.1242/dev.121.10.327910.1242/dev.121.10.32797588062Adams K. A., Maida J. M., Golden J. A., Riddle R. D. (2000). The transcription factor Lmx1b maintains Wnt1 expression within the isthmic organizer. Development 127, 1857–1867. 10.1242/dev.127.9.185710.1242/dev.127.9.185710751174Alexandre P., Wassef M. (2003). The isthmic organizer links anteroposterior and dorsoventral patterning in the mid/hindbrain by generating roof plate structures. Development 130, 5331–5338. 10.1242/dev.0075610.1242/dev.0075614507781Alonso A., Merchán P., Sandoval J. E., Sánchez-Arrones L., Garcia-Cazorla A., Artuch R., et al. (2013). Development of the serotonergic cells in murine raphe nuclei and their relations with rhombomeric domains. Brain Struct. Funct. 218, 1229–1277. 10.1007/s00429-012-0456-810.1007/s00429-012-0456-8PMC374832323052546Alvarado-Mallart R.-M. (1993). Fate and potentialities of the avian mesencephalic/metencephalic neuroepithelium. J. Neurobiol. 24, 1341–1355. 10.1002/neu.48024100710.1002/neu.4802410078228962Alvarado-Mallart R.-M. (1997). The chick/quail chimeric system: a model for early cerebellar development. Perspect. Dev. Neurobiol. 5, 17–31.9509515Alvarado-Mallart R.-M. (2000). “The chick/quail transplantation model to study central nervous system development,” in Functional Neural Transplantation II. Novel Cell Therapies For CNS Disorders. Progress in Brain Research, Vol. 127, eds S. B. Dunnett, and A. Bjorklund (Elsevier B.V.), 67–98, 10.1016/S0079-6123(00)27006-410.1016/S0079-6123(00)27006-411142048Alvarado-Mallart R.-M., Sotelo C. (1984). Homotopic and heterotopic transplantations of quail tectal primordia in chick embryos: organization of the retinotectal projections in the chimeric embryos. Dev. Biol. 103, 378–398. 10.1016/0012-1606(84)90326-910.1016/0012-1606(84)90326-96724134Alvarado-Mallart R.-M., Martinez S., Lance-Jones C. C. (1990). Pluripotentiality of the 2-day-old avian germinative neuroepithelium. Dev. Biol. 139, 75–88. 10.1016/0012-1606(90)90280-v10.1016/0012-1606(90)90280-v2328842Alvarez-Otero R., Sotelo C., Alvarado-Mallart R.-M. (1993). Chick/quail chimeras with partial cerebellar grafts: an analysis of the origin and migration of cerebellar cells. J. Comp. Neurol. 333, 597–615. 10.1002/cne.90333041110.1002/cne.9033304117690372Ang S. L., Jin O., Rhinn M., Daigle N., Stevenson L., Rossant J. (1996). A targeted mouse Otx2 mutation leads to severe defects in gastrulation and formation of axial mesoderm and to deletion of rostral brain. Development 122, 243–252. 10.1242/dev.122.1.24310.1242/dev.122.1.2438565836Araki I., Brand M. (2001). Morpholino-induced knockdown of Fgf8 efficiently phenocopies the acerebellar (ACE) phenotype. Genesis 30, 157–159. 10.1002/gene.105410.1002/gene.105411477697Araki I., Nakamura H. (1999). Engrailed defines the position of dorsal di-mesencephalic boundary by repressing diencephalic fate. Development 126, 5127–5135. 10.1242/dev.126.22.512710.1242/dev.126.22.512710529429Aroca P., Lorente-Cánovas B., Mateos F. R., Puelles L. (2006). Locus coeruleus neurons originate in alar rhombomere 1 and migrate into the basal plate: studies in chick and mouse embryos. J. Comp. Neurol. 496, 802–818. 10.1002/cne.2095710.1002/cne.2095716628617Aroca P., Puelles L. (2005). Postulated boundaries and differential fate in the developing rostral hindbrain. Brain Res. Rev. Res. Rev. 49, 179–190. 10.1016/j.brainresrev.2004.12.03110.1016/j.brainresrev.2004.12.03116111548Asano M., Gruss P. (1992). Pax-5 is expressed at the midbrain-hindbrain boundary during mouse development. Mech. Dev. 39, 29–39. 10.1016/0925-4773(92)90023-d10.1016/0925-4773(92)90023-d1283313Bally-Cuif L., Alvarado-Mallart R.-M., Darnell D. K., Wassef M. (1992). Relationship between Wnt-1 and En-2 expression domains during early development of normal and ectopic met-mesencephalon. Development 115, 999–1009. 10.1242/dev.115.4.99910.1242/dev.115.4.9991360404Bally-Cuif L., Gulisano M., Broccoli V., Boncinelli E. (1995). c-otx2 is expressed in two different phases of gastrulation and is sensitive to retinoic acid treatment in chick embryo. Mech. Dev. 49, 49–63. 10.1016/0925-4773(94)00301-310.1016/0925-4773(94)00301-37748789Bally-Cuif L., Wassef M. (1994). Ectopic induction and reorganization of Wnt-1 expression in quail/chick chimeras. Development 120, 3379–3394. 10.1242/dev.120.12.337910.1242/dev.120.12.33797821210Basson M. A., Echevarria D., Petersen Ahn C., Sudarov A., Joyner A. L., Mason I. J., et al. (2008). Specific regions within the embryonic midbrain and cerebellum require different levels of FGF signaling during development. Development 135, 889–898. 10.1242/dev.01156910.1242/dev.011569PMC255597818216176Belting H. G., Hauptmann G., Meyer D., Abdelilah-Seyfried S., Chitnis A., Eschbach C., et al. (2001). spiel ohne grenzen/pou2 is required during establishment of the zebrafish midbrain-hindbrain boundary organizer. Development 128, 4165–4176. 10.1242/dev.128.21.416510.1242/dev.128.21.4165PMC402796011684654Bilovocky N. A., Romito-DiGiacomo R. R., Murcia C. L., Maricich S. M., Herrup K. (2003). Factors in the genetic background suppress the Engrailed-1 cerebellar phenotype. J. Neurosci. 23, 5105–5112. 10.1523/JNEUROSCI.23-12-05105.200310.1523/JNEUROSCI.23-12-05105.2003PMC674114712832534Blak A. A., Naserken T., Saarimäki-Vire J., Peltopuro P., Giraldo-Velasquez M., Weisenhorn D. M. V., et al. (2007a). Fgfr2 and Fgfr3 are not required for patterning and maintenance of the midbrain and anterior hindbrain. Dev. Biol 303, 231–243. 10.1016/j.ydbio.2006.11.00810.1016/j.ydbio.2006.11.00817150206Blak A. A., Naserken T., Weisenhorn D. M. V., Prakash N., Partanen J., Wurst W. (2007b). Expression of Fgf receptors 1, 2 and 3 in the developing Mid- and hindbrain of the mouse. Dev. Dyn. 233, 1023–1030. 10.1002/dvdy.2038610.1002/dvdy.2038615830353Bloch-Gallego E., Millet S., Alvarado-Mallart R.-M. (1996). Further observations on the susceptibility of diencephalic prosomeres to En-2 induction and on the resulting histogenetic capabilities. Mech. Dev. 58, 51–63. 10.1016/s0925-4773(96)00557-610.1016/s0925-4773(96)00557-68887316Bosone C., Andreu A., Echevarria D. (2016). GAP junctional communication in brain secondary organizers. Dev. Growth Differ. 58, 446–455. 10.1111/dgd.1229710.1111/dgd.12297PMC1152098127273333Bouchard M., Grote D., Craven S. E., Sun Q., Steinlein P., Busslinger M. (2005). Identification of Pax2-regulated genes by expression profiling of the mid-hindbrain organizer region. Development 132, 2633–2643. 10.1242/dev.0183310.1242/dev.0183315872005Bouillet P., Chazaud C., Oulad-Abdelghani M., Dollé P., Chambon P. (1995). Sequence and expression pattern of the Stra7 (Gbx-2) homeobox-containing gene induced by retinoic acid in P19 embryonal carcinoma cells. Dev. Dyn. 204, 372–382. 10.1002/aja.100204040410.1002/aja.10020404048601031Brand M., Heisenberg C. P., Jiang Y. J., Beuchle D., Lun K., Furutani-Seiki M., et al. (1996). Mutations in zebrafish genes affecting the formation of the boundary between midbrain and hindbrain. Development 123, 179–190. 10.1242/dev.123.1.17910.1242/dev.123.1.1799007239Broccoli V., Boncinelli E., Wurst W. (1999). The caudal limit of Otx2 expression positions the isthmic organizer. Nature 401, 164–168. 10.1038/4367010.1038/4367010490025Buckles G. R., Thorpe C. J., Ramel M.-C., Lekven A. C. (2004). Combinatorial Wnt control of zebrafish midbrain-hindbrain boundary formation. Mech. Dev. 121, 437–447. 10.1016/j.mod.2004.03.02610.1016/j.mod.2004.03.02615147762Bueno D., Skinner J., Abud H., Heath J. K. (1996). Spatial and temporal relationships between Shh, Fgf4 and Fgf8 gene expression at diverse signalling centers during mouse development. Dev. Dyn. 207, 291–299. 10.1002/(SICI)1097-0177(199611)207:3<291::AID-AJA6>3.0.CO;2-C10.1002/(SICI)1097-0177(199611)207:3<291::AID-AJA6>3.0.CO;2-C8922528Bulfone A., Puelles L., Porteus M., Frohman M., Martin G., Rubenstein J. (1993). Spatially restricted expression of Dlx-1, Dlx-2 (Tes-1), Gbx-2 and Wnt- 3 in the embryonic day 12.5 mouse forebrain defines potential transverse and longitudinal segmental boundaries. J. Neurosci. 13, 3155–3172. 10.1523/JNEUROSCI.13-07-03155.199310.1523/JNEUROSCI.13-07-03155.1993PMC65766887687285Burgess S., Reim G., Chen W., Hopkins N., Brand M. (2002). The zebrafish spiel-ohne-grenzen (spg) gene encodes the POU domain protein Pou2 related to mammalian Oct4 and is essential for formation of the midbrain and hindbrain and for pre-gastrula morphogenesis. Development 129, 905–916. 10.1242/dev.129.4.90510.1242/dev.129.4.90511861474Burroughs-Garcia J., Sittaramane V., Chandrasekhar A., Waters S. T. (2011). Evolutionarily conserved function of Gbx2 in anterior hindbrain development. Dev. Dyn. 240, 828–838. 10.1002/dvdy.2258910.1002/dvdy.2258921360792Canning C. A., Lee L., Irving C., Mason I., Jones C. M. (2007). Sustained interactive Wnt and FGF signaling is required to maintain isthmic identity. Dev. Biol. 305, 276–286. 10.1016/j.ydbio.2007.02.00910.1016/j.ydbio.2007.02.00917383629Castro L. F. C., Rasmussen S. L. K., Holland P. W. H., Holland N. D., Holland L. Z. (2006). A Gbx homeobox gene in amphioxus: insights into ancestry of the ANTP class and evolution of the midbrain/hindbrain boundary. Dev. Biol. 295, 40–51. 10.1016/j.ydbio.2006.03.00310.1016/j.ydbio.2006.03.00316687133Chapouton P., Adolf B., Leucht C., Tannhäuser B., Ryu S., Driever W., et al. (2006). her5 expression reveals a pool of neural stem cells in the adult zebrafish midbrain. Development 133, 4293–4303. 10.1242/dev.0257310.1242/dev.0257317038515Cheng Y., Sudarov A., Szulc K. U., Sgaier S. K., Stephen D., Turnbull D. H., et al. (2010). The Engrailed homeobox genes determine the different foliation patterns in the vermis and hemispheres of the mammalian cerebellum. Development 137, 519–529. 10.1242/dev.02704510.1242/dev.027045PMC285891120081196Chi C. L., Martinez S., Wurst W., Martin G. R. (2003). The isthmic organizer signal FGF8 is required for cell survival in the prospective midbrain and cerebellum. Development 130, 2633–2644. 10.1242/dev.0048710.1242/dev.0048712736208Christen B., Slack J. M. W. (1997). FGF-8 is associated with anteroposterior patterning and limb regeneration in Xenopus. Dev. Biol. 192, 455–466. 10.1006/dbio.1997.873210.1006/dbio.1997.87329441681Crespo-Enriquez I., Partanen J., Martinez S., Echevarria D. (2012). Fgf8-related secondary organizers exert different polarizing planar instructions along the mouse anterior neural tube. PLoS One 7:e39977. 10.1371/journal.pone.003997710.1371/journal.pone.0039977PMC339122122792203Crossley P. H., Martin G. R. (1995). The mouse Fgf8 gene encodes a family of polypeptides and is expressed in regions that direct outgrowth and patterning in the developing embryo. Development 121, 439–451. 10.1242/dev.121.2.43910.1242/dev.121.2.4397768185Crossley P. H., Martinez S., Martin G. R. (1996). Midbrain development induced by FGF8 in the chick embryo. Nature 380, 66–68. 10.1038/380066a010.1038/380066a08598907Danielian P. S., McMahon A. P. (1996). Engrailed-1 as a target of the Wnt-1 signalling pathway in vertebrate midbrain development. Nature 383, 332–334. 10.1038/383332a010.1038/383332a08848044Davidson D., Graham E., Sime C., Hill R. (1988). A gene with sequence similarity to Drosophila engrailed is expressed during the development of the neural tube and vertebrae in the mouse. Development 104, 305–316. 10.1242/dev.104.2.30510.1242/dev.104.2.3052908202Davis C. A., Holmyard D. P., Millen K. J., Joyner A. L. (1991). Examining pattern formation in mouse, chicken and frog embryos with an En-specific antiserum. Development 111, 287–298. 10.1242/dev.111.2.28710.1242/dev.111.2.2871680044Davis C. A., Joyner A. L. (1988). Expression patterns of the homeo box-containing genes En-1 and En-2 and the proto-oncogene int-1 diverge during mouse development. Genes Dev. 2, 1736–1744. 10.1101/gad.2.12b.173610.1101/gad.2.12b.17362907320Delgado I., Torres M. (2017). Coordination of limb development by crosstalk among axial patterning pathways. Dev. Biol. 429, 382–386. 10.1016/j.ydbio.2017.03.00610.1016/j.ydbio.2017.03.00628283405Dworkin S., Darido C., Georgy S. R., Wilanowski T., Srivastava S., Ellett F., et al. (2012). Midbrain-hindbrain boundary patterning and morphogenesis are regulated by diverse grainy head-like 2-dependent pathways. Development 139, 525–536. 10.1242/dev.06652210.1242/dev.06652222223680Dyer C., Blanc E., Hanisch A., Roehl H., Otto G. W., Yu T., et al. (2014). A bi-modal function of Wnt signalling directs an FGF activity gradient to spatially regulate neuronal differentiation in the midbrain. Development 141, 63–72. 10.1242/dev.09950710.1242/dev.099507PMC386575024284206Echevarria D., Belo J. A., Martinez S. (2005). Modulation of Fgf8 activity during vertebrate brain development. Brain Res. Rev. 49, 150–157. 10.1016/j.brainresrev.2004.12.03510.1016/j.brainresrev.2004.12.03516111545Ekker M., Wegner J., Akimenko M. A., Westerfield M. (1992). Coordinate embryonic expression of three zebrafish engrailed genes. Development 116, 1001–1010. 10.1242/dev.116.4.100110.1242/dev.116.4.10011363539Favor J., Sandulache R., Neuhauser-Klaus A., Pretsch W., Chatterjee B., Senft E., et al. (1996). The mouse Pax21Neu mutation is identical to a human PAX2 mutation in a family with renal-coloboma syndrome and results in developmental defects of the brain, ear, eye and kidney. Proc. Natl. Acad. Sci. U S A 93, 13870–13875. 10.1073/pnas.93.24.1387010.1073/pnas.93.24.13870PMC194538943028Finkelstein R., Boncinelli E. (1994). From fly head to mammalian forebrain: the story of otd and Otx. Trends Genet. 10, 310–315. 10.1016/0168-9525(94)90033-710.1016/0168-9525(94)90033-77974744Foucher I., Mione M., Simeone A., Acampora D., Bally-Cuif L., Houart C. (2006). Differentiation of cerebellar cell identities in absence of Fgf signalling in zebrafish Otx morphants. Development 133, 1891–1900. 10.1242/dev.0235210.1242/dev.0235216611693Friedman G. C., O’Leary D. D. M. (1996). Retroviral misexpression of engrailed genes in the chick optic tectum perturbs the topographic targeting of retinal axons. J. Neurosci. 16, 5498–5509. 10.1523/JNEUROSCI.16-17-05498.199610.1523/JNEUROSCI.16-17-05498.1996PMC65788758757262Friesel R., Brown S. A. (1992). Spatially restricted expression of fibroblast growth factor receptor-2 during Xenopus development. Development 116, 1051–1058. 10.1242/dev.116.4.105110.1242/dev.116.4.10511284237Funahashi J., Okafuji T., Ohuchi H., Noji S., Tanaka H., Nakamura H. (1999). Role of Pax-5 in the regulation of a mid-hindbrain organizer’s activity. Dev. Growth Differ. 41, 59–72. 10.1046/j.1440-169x.1999.00401.x10.1046/j.1440-169x.1999.00401.x10445503Galant S., Furlan G., Coolen M., Dirian L., Foucher I., Bally-Cuif L. (2016). Embryonic origin and lineage hierarchies of the neural progenitor subtypes building the zebrafish adult midbrain. Dev. Biol. 420, 120–135. 10.1016/j.ydbio.2016.09.02210.1016/j.ydbio.2016.09.022PMC515651727693369Garda A. L., Echevarría D., Martínez S. (2001). Neuroepithelial co-expression of Gbx2 and Otx2 precedes Fgf8 expression in the isthmic organizer. Mech. Dev. 101, 111–118. 10.1016/s0925-4773(00)00567-010.1016/s0925-4773(00)00567-011231064Gardner C. A., Barald K. F. (1991). The cellular environment controls the expression of engrailed-like protein in the cranial neuroepithelium of quail-chick chimeric embryos. Development 113, 1037–1048. 10.1242/dev.113.3.103710.1242/dev.113.3.10371687983Gardner C. A., Darnell D. K., Poole S. J., Ordahl C. P., Barald K. F. (1988). Expression of anengrailed-like gene during development of the early embryonic chick nervous system. J. Neurosci. Res. 21, 426–437. 10.1002/jnr.49021023410.1002/jnr.4902102342464080Geling A., Itoh M., Tallafuβ A., Chapouton P., Tannhäuser B., Kuwada J. Y., et al. (2003). bHLH transcription factor Her5 links patterning to regional inhibition of neurogenesis at the midbrain-hindbrain boundary. Development 130, 1591–1604. 10.1242/dev.0037510.1242/dev.0037512620984Geling A., Plessy C., Rastegar S., Strähle U., Bally-Cuif L. (2004). Her5 acts as a prepattern factor that blocks neurogenin1 and coe2 expression upstream of Notch to inhibit neurogenesis at the midbrain-hindbrain boundary. Development 131, 1993–2006. 10.1242/dev.0109310.1242/dev.0109315056616Goode D. K., Elgar G. (2009). The PAX258 gene subfamily: a comparative perspective. Dev. Dyn. 238, 2951–2974. 10.1002/dvdy.2214610.1002/dvdy.2214619924770Grapin-Botton A., Cambronero F., Weiner H. L., Bonnin M.-A., Puelles L., Le Douarin N. M. (1999). Patterning signals acting in the spinal cord override the organizing activity of the isthmus. Mech. Dev. 84, 41–53. 10.1016/s0925-4773(99)00069-610.1016/s0925-4773(99)00069-610473119Green D. G., Whitener A. E., Mohanty S., Mistretta B., Gunaratne P., Yeh A. T., et al. (2020). Wnt signaling regulates neural plate patterning in distinct temporal phases with dynamic transcriptional outputs. Dev. Biol. 462, 152–164. 10.1016/j.ydbio.2020.03.01610.1016/j.ydbio.2020.03.016PMC726809132243887Guo C., Qiu H. Y., Huang Y. H., Chen H., Yang R. Q., Chen S. D., et al. (2007). Lmx1b is essential for Fgf8 and Wnt1 expression in the isthmic organizer during tectum and cerebellum development in mice. Development 134, 317–325. 10.1242/dev.0274510.1242/dev.0274517166916Hallonet M. E., Teillet M. A., Le Douarin N. M. (1990). A new approach to the development of the cerebellum provided by the quail-chick marker system. Development 108, 18–31. 10.1242/dev.108.1.1910.1242/dev.108.1.192351063Hanks M., Wurst W., Anson-Cartwright L., Auerbach A. B., Joyner A. L. (1995). Rescue of the En-1 mutant phenotype by replacement of En-1 with En-2. Science 269, 679–682. 10.1126/science.762479710.1126/science.76247977624797Hauptmann G., Belting H. G., Wolke U., Lunde K., Söll I., Abdelilah-Seyfried S., et al. (2002). spiel ohne grenzen/pou2 is required for zebrafish hindbrain segmentation. Development 129, 1645–1655. 10.1242/dev.129.7.164510.1242/dev.129.7.164511923201Heikinheimo M., Lawshé A., Shackleford G. M., Wilson D. B., MacArthur C. A. (1994). Fgf-8 expression in the post-gastrulation mouse suggests roles in the development of the face, limbs and central nervous system. Mech. Dev. 48, 129–138. 10.1016/0925-4773(94)90022-110.1016/0925-4773(94)90022-17873403Heller N., Brändli A. W. (1997). Xenopus Pax-2 displays multiple splice forms during embryogenesis and pronephric kidney development. Mech. Dev. 69, 83–104. 10.1016/s0925-4773(97)00158-510.1016/s0925-4773(97)00158-59486533Hemmati-Brivanlou A., de-la-Torre J. R., Holt C., Harland R. M. (1991). Cephalic expression and molecular characterization of Xenopus En-2. Development 111, 715–724. 10.1242/dev.111.3.71510.1242/dev.111.3.7151679005Hidalgo-Sánchez M., Alvarado-Mallart R.-M. (2002). Temporal sequence of gene expression leading caudal prosencephalon to develop a midbrain/hindbrain phenotype. Dev. Dyn. 223, 141–147. 10.1002/dvdy.122410.1002/dvdy.122411803577Hidalgo-Sánchez M., Millet S., Bloch-Gallego E., Alvarado-Mallart R.-M. (2005a). Specification of the meso-isthmo-cerebellar region: the Otx2/Gbx2 boundary. Brain Res. Rev. 49, 134–149. 10.1016/j.brainresrev.2005.01.01010.1016/j.brainresrev.2005.01.01016111544Hidalgo-Sánchez M., Martínez-de-la-Torre M., Alvarado-Mallart R.-M., Puelles L. (2005b). A distinct preisthmic histogenetic domain is defined by overlap of Otx2 and Pax2 gene expression in the avian caudal midbrain. J. Comp. Neurol. 483, 17–29. 10.3390/s2203108010.3390/s2203108015672400Hidalgo-Sánchez M., Millet S., Simeone A., Alvarado-Mallart R.-M. (1999a). Comparative analysis of Otx2, Gbx2, Pax2, Fgf8 and Wnt1 gene expressions during the formation of the chick midbrain/hindbrain domain. Mech. Dev. 81, 175–178. 10.1016/s0925-4773(98)00224-x10.1016/s0925-4773(98)00224-x10330495Hidalgo-Sánchez M., Simeone A., Alvarado-Mallart R.-M. (1999b). Fgf8 and Gbx2 induction concomitant with Otx2 repression is correlated with midbrain-hindbrain fate of caudal prosencephalon. Development 126, 3191–3203. 10.1242/dev.126.14.319110.1242/dev.126.14.319110375509Hirata H., Tomita K., Bessho Y., Kageyama R. (2001). Hes1 and Hes3 regulate maintenance of the isthmic organizer and development of the mid/hindbrain. EMBO J. 20, 4454–4466. 10.1093/emboj/20.16.445410.1093/emboj/20.16.4454PMC12558311500373Hollyday M., McMahon J. A., McMahon A. P. (1995). Wnt expression patterns in chick embryo nervous system. Mech. Dev. 52, 9–25. 10.1016/0925-4773(95)00385-e10.1016/0925-4773(95)00385-e7577679Inomata C., Yuikawa T., Nakayama-Sadakiyo Y., Kobayashi K., Ikeda M., Chiba M., et al. (2020). Involvement of an Oct4-related PouV gene, pou5f3/pou2, in neurogenesis in the early neural plate of zebrafish embryos. Dev. Biol. 457, 30–42. 10.1016/j.ydbio.2019.09.00210.1016/j.ydbio.2019.09.00231520602Inoue F., Kurokawa D., Takahashi M., Aizawa S. (2012). Gbx2 Directly Restrictssource. Otx2 expression to forebrain and midbrain, competing with Class III POU Factors. Mol. Cel. Biol. 32, 2618–2627. 10.1128/MCB.00083-1210.1128/MCB.00083-12PMC343448022566684Irving C., Mason I. (1999). Regeneration of isthmic tissue is the result of a specific and direct interaction between rhombomere 1 and midbrain. Development 126, 3981–3989. 10.1242/dev.126.18.398110.1242/dev.126.18.398110457008Islam M. E., Kikuta H., Inoue F., Kanai M., Kawakami A., Parvin M. S., et al. (2006). Three enhancer regions regulate gbx2 gene expression in the isthmic region during zebrafish development. Mech. Dev. 123, 907–924. 10.1016/j.mod.2006.08.00710.1016/j.mod.2006.08.00717067785Issack P. S., Ziff E. B. (1998). Altered expression of helix-loop-helix transcriptional regulators and cyclin D1 in Wnt-1-transformed PC12 cells. Cell Growth Differ. 9, 837–845.9790495Itasaki N., Nakamura H. (1992). Rostrocaudal polarity of the tectum in birds: correlation of en gradient and topographic order in retinotectal projection. Neuron 8, 787–798. 10.1016/0896-6273(92)90099-y10.1016/0896-6273(92)90099-y1348950Itasaki N., Nakamura H. (1996). A role for gradient en expression in positional specification on the optic tectum. Neuron 16, 55–62. 10.1016/s0896-6273(00)80023-910.1016/s0896-6273(00)80023-98562091Itasaki N., Ichijo H., Hama C., Matsuno T., Nakamura H. (1991). Establishment of rostrocaudal polarity in tectal primordium: engrailed expression and subsequent tectal polarity. Development 113, 1133–1144. 10.1242/dev.113.4.113310.1242/dev.113.4.11331811932Jászai J., Reifers F., Picker A., Langenberg T., Brand M. (2003). Isthmus-to-midbrain transformation in the absence of midbrain-hindbrain organizer activity. Development 130, 6611–6623. 10.1242/dev.0089910.1242/dev.0089914660549Joyner A. L., Herrup K., Auerbach B. A., Davis C. A., Rossant J. (1991). Subtle cerebellar phenotype in mice homozygous for a targeted deletion of the En-2 homeobox. Science 251, 1239–1243. 10.1126/science.167247110.1126/science.16724711672471Joyner A. L., Kornberg T., Coleman K. G., Cox D. R., Martin G. R. (1985). Expression during embryogenesis of a mouse gene with sequence homology to the Drosophila engrailed gene. Cell 43, 29–37. 10.1016/0092-8674(85)90009-110.1016/0092-8674(85)90009-12416459Joyner A. L., Martin G. R. (1987). En-1 and En-2, two mouse genes with sequence homology to the Drosophila engrailed gene: expression during embryogenesis. Genes Dev. 1, 29–38. 10.1101/gad.1.1.2910.1101/gad.1.1.292892757Joyner A. L., Skarnes W. C., Rossant J. (1989). Production of a mutation in mouse En-2 gene by homologous recombination in embryonic stem cells. Nature 338, 153–156. 10.1038/338153a010.1038/338153a02563902Jukkola T., Lahti L., Naserke T., Wurst W., Partanen J. (2006). FGF regulated gene-expression and neuronal differentiation in the developing midbrain-hindbrain region. Dev. Biol. 297, 141–157. 10.1016/j.ydbio.2006.05.00210.1016/j.ydbio.2006.05.00216782087Jungbluth S., Larsen C., Wizenmann A., Lumsden A. (2001). Cell mixing between the embryonic midbrain and hindbrain. Curr. Biol. 11, 204–207. 10.1016/s0960-9822(01)00049-510.1016/s0960-9822(01)00049-511231158Kala K., Jukkola T., Pata I., Partanen J. (2008). Analysis of the midbrain-hindbrain boundary cell fate using a boundary cell-specific Cre-mouse strain. Genesis 46, 29–36. 10.1002/dvg.2034410.1002/dvg.2034418196597Katahira T., Sato T., Sugiyama S., Okafuji T., Araki I., Funahashi J., et al. (2000). Interaction between Otx2 and Gbx2 defines the organizing center for the optic tectum. Mech. Dev. 91, 43–52. 10.1016/s0925-4773(99)00262-210.1016/s0925-4773(99)00262-210704829Kelly G. M., Moon R. T. (1995). Involvement of Wnt1 and Pax2 in the formation of the midbrain-hindbrain boundary in the zebrafish gastrula. Dev. Genet. 17, 129–140. 10.1016/s0925-4773(99)00262-210.1016/s0925-4773(99)00262-27586754Kesavan G., Chekuru A., Machate A., Brand M. (2017). CRISPR/Cas9-mediated zebrafish knock-in as a novel strategy to study midbrain-hindbrain boundary development. Front. Neuroanat. 11:52. 10.3389/fnana.2017.0005210.3389/fnana.2017.00052PMC549265728713249Kesavan G., Hammer J., Hans S., Brand M. (2018). Targeted knock-in of CreERT2 in zebrafish using CRISPR/Cas9. Cell Tissue Res. 372, 41–50. 10.1007/s00441-018-2798-x10.1007/s00441-018-2798-x29435650Kesavan G., Machate A., Hans S., Brand M. (2020). Cell-fate plasticity, adhesion and cell sorting complementarily establish a sharp midbrain-hindbrain boundary. Development 147:dev186882. 10.1242/dev.18688210.1242/dev.18688232439756Kikuta H., Kanai M., Ito Y., Yamasu K. (2003). gbx2 Homeobox gene is required for the maintenance of the isthmic region in the zebrafish embryonic brain. Dev. Dyn. 228, 433–450. 10.1002/dvdy.1040910.1002/dvdy.1040914579382Kim S., Zhao Y., Lee J. M., Kim W. R., Gorivodsky M., Westphal H., et al. (2016). Ldb1 is essential for the development of isthmic organizer and midbrain dopaminergic neurons. Stem Cells Dev. 25, 986–994. 10.1089/scd.2015.030710.1089/scd.2015.0307PMC493278127171818Kimura J., Katahira T., Araki I., Nakamura H. (2004). Possible role of Hes5 for the rostrocaudal polarity formation of the tectum. Dev. Growth Differ. 46, 219–227. 10.1111/j.1440-169X.2004.00739.x10.1111/j.1440-169X.2004.00739.x15206953Kitajima K., Koshimizu U., Nakamura T. (1999). Expression of a novel type of classic cadherin, PB-cadherin in developing brain and limb buds. Dev. Dyn. 215, 206–214. 10.1002/(SICI)1097-0177(199907)215:3<206::AID-AJA3>3.0.CO;2-X10.1002/(SICI)1097-0177(199907)215:3<206::AID-AJA3>3.0.CO;2-X10398531Krauss S., Johansen T., Korzh V., Fjose A. (1991). Expression of the zebrafish paired box gene pax[zf-b] during early neurogenesis. Development 113, 1193–1206. 10.1242/dev.113.4.119310.1242/dev.113.4.11931811936Krauss S., Maden M., Holder N., Wilson S. W. (1992). Zebrafish pax[b] is involved in the formation of the midbrain-hindbrain boundary. Nature 360, 87–89. 10.1038/360087a010.1038/360087a01436081Kurokawa D., Kiyonari H., Nakayama R., Kimura-Yoshida C., Matsuo I., Aizawa S. (2004). Regulation of Otx2 expression and its functions in mouse forebrain and midbrain. Development 131, 3319–3331. 10.1242/dev.0122010.1242/dev.0122015201224Lahti L., Saarimäki-Vire J., Rita H., Partanen J. (2011). FGF signaling gradient maintains symmetrical proliferative divisions of midbrain neuronal progenitors. Dev. Biol. 349, 270–282. 10.1016/j.ydbio.2010.11.00810.1016/j.ydbio.2010.11.00821074523Langenberg T., Brand M. (2005). Lineage restriction maintains a stable organizer cell population at the zebrafish midbrain-hindbrain boundary. Development 132, 3209–3216. 10.1242/dev.0186210.1242/dev.0186215958515Le Douarin N. M. (1969). Particularites du noyau interphasique chez la caille japonaise (Coturnix coturnix japonica). Bull. Biol. Fr. Belg. 103, 435–452.4191116Le Douarin N. M. (1973). A feulgen-positive nucleolus. Exp. Cell Res. 77, 459–468. 10.1016/0014-4827(73)90600-910.1016/0014-4827(73)90600-94120441Leerberg D. M., Hopton R. E., Draper B. W. (2019). Fibroblast growth factor receptors function redundantly during zebrafish embryonic development. Genetics 212, 1301–1319. 10.1534/genetics.119.30234510.1534/genetics.119.302345PMC670745831175226Lekven A. C., Buckles G. R., Kostakis N., Moon R. T. (2003). wnt1 and wnt10b function redundantly at the zebrafish midbrain-hindbrain boundary. Dev. Biol. 254, 172–187. 10.1016/s0012-1606(02)00044-110.1016/s0012-1606(02)00044-112591239Li J. Y., Joyner A. L. (2001). Otx2 and Gbx2 are required for refinement and not induction of mid-hindbrain gene expression. Development 128, 4979–4991. 10.1242/dev.128.24.497910.1242/dev.128.24.497911748135Li J. Y. H., Lao Z., Joyner A. L. (2002). Changing requirements for Gbx2 in development of the cerebellum and maintenance of the mid/hindbrain organizer. Neuron 36, 31–43. 10.1016/s0896-6273(02)00935-210.1016/s0896-6273(02)00935-212367504Li J. Y. H., Lao Z., Joyner A. L. (2005). New regulatory interactions and cellular responses in the isthmic organizer region revealed by altering Gbx2 expression. Development 132, 1971–1981. 10.1242/dev.0172710.1242/dev.0172715790971Liu A., Joyner A. L. (2001). EN and GBX2 play essential roles downstream of FGF8 in patterning the mouse mid/hindbrain region. Development 128, 181–191. 10.1242/dev.128.2.18110.1242/dev.128.2.18111124114Liu A., Li J. H. L., Bromleigh C., Lao Z., Niswander L. A., Joyner A. L. (2003). FGF17b and FGF18 have different midbrain regulatory properties from FGF8b or activated FGF receptors. Development 130, 6175–6185. 10.1242/dev.0084510.1242/dev.0084514602678Liu A., Losos K., Joyner A. L. (1999). FGF8 can activate Gbx2 and transform regions of the rostral mouse brain into a hindbrain fate. Development 126, 4827–4838. 10.1242/dev.126.21.482710.1242/dev.126.21.482710518499Lobe C. G. (1997). Expression of the helix-loop-helix factor, Hes3, during embryo development suggests a role in early midbrain-hindbrain patterning. Mech. Dev. 62, 227–237. 10.1016/s0925-4773(97)00665-510.1016/s0925-4773(97)00665-59152013Logan C., Hanks M. C., Noble-Topham S., Nallainathan D., Provart N. J., Joyner A. L. (1992). Cloning and sequence comparison of the mouse, human and chicken engrailed genes reveal potential functional domains and regulatory regions. Dev. Genet. 13, 345–358. 10.1002/dvg.102013050510.1002/dvg.10201305051363401Logan C., Wizenmann A., Drescher U., Monschau B., Bonhoeffer F., Lumsden A. (1996). Rostral optic tectum acquires caudal characteristics following ectopic engrailed expression. Curr. Biol. 6, 1006–1014. 10.1016/s0960-9822(02)00645-010.1016/s0960-9822(02)00645-08805331Lorente-Cánovas B., Marín F., Corral-San-Miguel R., Hidalgo-Sánchez M., Ferran J. L., Puelles L., et al. (2012). Multiple origins, migratory paths and molecular profiles of cells populating the avian interpeduncular nucleus. Dev. Biol. 361, 12–26. 10.1016/j.ydbio.2011.09.03210.1016/j.ydbio.2011.09.03222019302Louvi A., Alexandre P., Me?tin C., Wurst W., Wassef M. (2003). The isthmic neuroepithelium is essential for cerebellar midline fusion. Development 130, 5319–5330. 10.1242/dev.0073610.1242/dev.0073614507778Lun K., Brand M. (1998). A series of no isthmus (noi) alleles of the zebrafish pax2.1 gene reveals multiple signaling events in development of the midbrain-hindbrain boundary. Development 125, 3049–3062. 10.1242/dev.125.16.304910.1242/dev.125.16.30499671579Müller M., von Weizsäcker E., Campos-Ortega J. A. (1996). Transcription of a zebrafish gene of the hairy-enhancer of split family delineates the midbrain anlage in the neural plate. Dev. Genes Evol. 206, 153–160. 10.1007/s00427005004110.1007/s00427005004124173468Marín F., Puelles L. (1994). Patterning of the embryonic avian midbrain after experimental inversions: a polarizing activity from the isthmus. Dev. Biol. 163, 19–37. 10.1006/dbio.1994.112010.1006/dbio.1994.11208174775Marín F., Puelles L. (1995). Morphological fate of rhombomeres in quail/chick chimeras: a segmental analysis of hindbrain nuclei. Eur. J. Neurosci. 7, 1714–1738. 10.1111/j.1460-9568.1995.tb00693.x10.1111/j.1460-9568.1995.tb00693.x7582126Martinez S., Alvarado-Mallart R.-M. (1989). Rostral cerebellum originates from the caudal portion of the so-called “mesencephalic” vesicle: a study using Chick/Quail chimeras. Eur. J. Neurosci. 1, 549–560. 10.1111/j.1460-9568.1989.tb00362.x10.1111/j.1460-9568.1989.tb00362.x12106114Martinez S., Alvarado-Mallart R.-M. (1990). Expression of the homeobox Chick-en gene in chick/quail chimeras with inverted mes-metencephalic grafts. Dev. Biol. 139, 432–436. 10.1016/0012-1606(90)90312-710.1016/0012-1606(90)90312-71970967Martinez S., Crossley P. H., Cobos I., Rubenstein J. L., Martin G. R. (1999). FGF8 induces formation of an ectopic isthmic organizer and isthmocerebellar development via a repressive effect on Otx2 expression. Development 126, 1189–1200. 10.1242/dev.126.6.118910.1242/dev.126.6.118910021338Martínez S., Marín F., Nieto M. A., Puelles L. (1995). Induction of ectopic engrailed expression and fate change in avian rhombomeres: intersegmental boundaries as barriers. Mech. Dev. 51, 289–303. 10.1016/0925-4773(95)00376-210.1016/0925-4773(95)00376-27547475Martinez S., Wassef M., Alvarado-Mallart R.-M. (1991). Induction of a mesencephalic phenotype in the 2-day-old chick prosencephalon is preceded by the early expression of the homeobox gene en. Neuron 6, 971–981. 10.1016/0896-6273(91)90237-t10.1016/0896-6273(91)90237-t1675863Martinez-Barbera J. P., Signore M., Boyl P. P., Puelles E., Acampora D., Gogoi R., et al. (2001). Regionalisation of anterior neuroectoderm and its competence in responding to forebrain and midbrain inducing activities depend on mutual antagonism between OTX2 and GBX2. Development 128, 4789–4800. 10.1242/dev.128.23.478910.1242/dev.128.23.478911731459Matsunaga E., Araki I., Nakamura H. (2000). Pax6 defines the di-mesencephalic boundary by repressing En1 and Pax2. Development 127, 2357–2365. 10.1242/dev.127.11.235710.1242/dev.127.11.235710804178Matsunaga E., Katahira T., Nakamura H. (2002). Role of Lmx1b and Wnt1 in mesencephalon and metencephalon development. Development 129, 5269–5277. 10.1242/dev.129.22.526910.1242/dev.129.22.526912399317Matsuno T., Ichijo H., Nakamura H. (1991). Regulation of the rostrocaudal axis of the optic tectum: histological study after rostrocaudal rotation in quail-chick chimeras. Dev. Brain Res. 58, 265–270. 10.1016/0165-3806(91)90014-a10.1016/0165-3806(91)90014-a2029770Matsuo I., Kuratani S., Kimura C., Takeda N., Aizawa S. (1995). Mouse Otx2 functions in the formation and patterning of rostral head. Genes Dev. 9, 2646–2658. 10.1101/gad.9.21.264610.1101/gad.9.21.26467590242McMahon A. P., Bradley A. (1990). The Wnt-1 (int-1) proto-oncogene is required for development of a large region of the mouse brain. Cell 62, 1073–1085. 10.1016/0092-8674(90)90385-r10.1016/0092-8674(90)90385-r2205396McMahon A. P., Joyner A. L., Bradley A., McMahon J. A. (1992). The midbrain-hindbrain phenotype of Wnt-1−Wnt-1− mice results from stepwise deletion of engrailed-expressing cells by 9.5 days postcoitum. Cell 69, 581–595. 10.1016/0092-8674(92)90222-x10.1016/0092-8674(92)90222-x1534034Meinhardt H. (2009). Models for the generation and interpretation of gradients. Cold Spring Harb. Perspect. Biol. 1:a001362. 10.1101/cshperspect.a00136210.1101/cshperspect.a001362PMC277362220066097Mercier P., Simeone A., Cotelli F., Boncinelli E. (1995). Expression pattern of two otx genes suggests a role in specifying anterior body structures in zebrafish. Int. J. Dev. Biol 39, 559–573.8619954Meyers E. N., Lewandoski M., Martin G. R. (1998). An Fgf8 mutant allelic series generated by Cre- and Flp-mediated recombination. Nat. Genet. 18, 136–141. 10.1038/ng0298-13610.1038/ng0298-1369462741Miles L. B., Darido C., Kaslin J., Heath J. K., Jane S. M., Dworkin S. (2017). Mis-expression of grainyhead-like transcription factors in zebrafish leads to defects in enveloping layer (EVL) integrity, cellular morphogenesis and axial extension. Sci. Rep. 7:17607. 10.1038/s41598-017-17898-710.1038/s41598-017-17898-7PMC573056329242584Millen K. J., Wurst W., Herrup K., Joyner A. L. (1994). Abnormal embryonic cerebellar development and patterning of postnatal foliation in two mouse Engrailed-2 mutants. Development 120, 695–706. 10.1242/dev.120.3.69510.1242/dev.120.3.6957909289Millet S., Alvarado-Mallart R.-M. (1995). Expression of the homeobox-containing gene En-2 during the development of the chick central nervous system. Eur. J. Neurosci. 7, 777–791. 10.1111/j.1460-9568.1995.tb00681.x10.1111/j.1460-9568.1995.tb00681.x7620626Millet S., Bloch-Gallego E., Simeone A., Alvarado-Mallart R.-M. (1996). The caudal limit of Otx2 gene expression as a marker of the midbrain/hindbrain boundary: a study using in situ hybridisation and chick/quail homotopic grafts. Development 122, 3785–3797. 10.1242/dev.122.12.378510.1242/dev.122.12.37859012500Millet S., Campbell K., Epstein D. J., Losos K., Harris E., Joyner A. L. (1999). A role for Gbx2 in repression of Otx2 and positioning the mid/hindbrain organizer. Nature 401, 161–164. 10.1038/4366410.1038/4366410490024Molven A., Njølstad P. R., Fjose A. (1991). Genomic structure and restricted neural expression of the zebrafish wnt-1 (int-1) gene. EMBO J. 10, 799–807.PMC4527192009859Mori H., Miyazaki Y., Morita T., Nitta H., Mishina M. (1994). Different spatio-temporal expressions of three otx homeoprotein transcripts during zebrafish embryogenesis. Brain Res. Mol. Brain Res. 27, 221–231. 10.1016/0169-328x(94)90004-310.1016/0169-328x(94)90004-37898305Nakamura H. (1990). Do CNS anlagen have plasticity in differentiation? Analysis in quail-chick chimera. Brain Res. 511, 122–128. 10.1016/0006-8993(90)90231-y10.1016/0006-8993(90)90231-y2331610Nakamura H., Matsui K. A., Takagi S., Fujisawa H. (1991). Projection of the retinal ganglion cells to the tectum differentiated from the prosencephalon. Neurosci. Res. 11, 189–197. 10.1016/0168-0102(91)90042-w10.1016/0168-0102(91)90042-w1661870Nakayama Y., Inomata C., Yuikawa T., Tsuda S., Yamasu K. (2017). Comprehensive analysis of target genes in zebrafish embryos reveals gbx2 involvement in neurogenesis. Dev. Biol. 430, 237–248. 10.1016/j.ydbio.2017.07.01510.1016/j.ydbio.2017.07.01528756106Nakayama Y., Kikuta H., Kanai M., Yoshikawa K., Kawamura A., Kobayashi K., et al. (2013). Gbx2 functions as a transcriptional repressor to regulate the specification and morphogenesis of the mid-hindbrain junction in a dosage- and stage-dependent manner. Mech. Dev. 130, 532–552. 10.1016/j.mod.2013.07.00410.1016/j.mod.2013.07.00423933069Namm A., Arend A., Aunapuu M. (2014). Expression of Pax2 protein during the formation of the central nervous system in human embryos. Folia Morphol. (Warsz) 73, 272–278. 10.5603/FM.2014.004310.5603/FM.2014.004325346342Ninkovic J., Stigloher C., Lillesaar C., Bally-Cuif L. (2008). Gsk3ß/PKA and Gli1 regulate the maintenance of neural progenitors at the midbrain-hindbrain boundary in concert with E(Spl) factor activity. Development 135, 3137–3148. 10.1242/dev.02047910.1242/dev.02047918725518Ninkovic J., Tallafuß A., Leucht C., Topczewski J., Tannhäuser B., Solnica-Krezel L., et al. (2005). Inhibition of neurogenesis at the zebrafish midbrain-hindbrain boundary by the combined and dose-dependent activity of a new hairy/E(spl) gene pair. Development 132, 75–88. 10.1242/dev.0152510.1242/dev.0152515590746Niss K., Leutz A. (1998). Expression of the homeobox gene GBX2 during chicken development. Mech. Dev. 76, 151–155. 10.1016/s0925-4773(98)00103-810.1016/s0925-4773(98)00103-89767154O’Hara F. P., Beck E., Barr L. K., Wong L. L., Kessier D. S., Riddle R. D. (2005). Zebrafish Lmx1b.1 and Lmb1b.2 are required for maintenance of the isthmic organizer. Development 132, 3163–3173. 10.1242/dev.0189810.1242/dev.01898PMC136111815944182Ohuchi H., Kimura S., Watamoto M., Itoh N. (2000). Involvement of fibroblast growth factor (FGF)18-FGF8 signaling in specification of left-right asymmetry and brain and limb development of the chick embryo. Mech. Dev. 95, 55–66. 10.1016/s0925-4773(00)00331-210.1016/s0925-4773(00)00331-210906450Ohuchi H., Yoshioka H., Tanaka A., Kawakami Y., Nohno T., Noji S. (1994). Involvement of androgen-induced growth factor (FGF-8) gene in mouse embryogenesis and morphogenesis. Biochem. Biophys. Res. Commun. 204, 882–888. 10.1006/bbrc.1994.254210.1006/bbrc.1994.25427980556Okafuji T., Funahashi J., Nakamura H. (1999). Roles of Pax-2 in initiation of the chick tectal development. Dev. Brain Res. 116, 41–49. 10.1016/s0165-3806(99)00073-510.1016/s0165-3806(99)00073-510446345Olander S., Nordström U., Patthey C., Edlund T. (2006). Convergent Wnt and FGF signaling at the gastrula stage induce the formation of the isthmic organizer. Mech. Dev. 123, 166–176. 10.1016/j.mod.2005.11.00110.1016/j.mod.2005.11.00116413176Omi M., Harada H., Watanabe Y., Funahashi J., Nakamura H. (2014). Role of En2 in the tectal laminar formation of chick embryos. Development 141, 2131–2138. 10.1242/dev.10290510.1242/dev.10290524803658Omi M., Nakamura H. (2015). Engrailed and tectum development. Dev. Growth Differ. 57, 135–145. 10.1111/dgd.1219710.1111/dgd.1219725716935Orr H. (1887). Contribution to the embryology of the lizard; with especial reference to the central nervous system and some organs of the head; together with observations on the origin of the vertebrates. J. Morphol. 1, 311–372.Ota S., Tonou-Fujimori N., Nakayama Y., Ito Y., Kawamura A., Yamasu K. (2010). FGF receptor gene expression and its regulation by FGF signaling during early zebrafish development. Genesis 48, 707–716. 10.1002/dvg.2068210.1002/dvg.2068220960516Ota S., Taimatsu K., Yanagi K., Namiki T., Ohga R., Higashijima S., et al. (2016). Functional visualization and disruption of targeted genes using CRISPR/Cas9-mediated eGFP reporter integration in zebrafish. Sci. Rep. 6:34991. 10.1038/srep3499110.1038/srep34991PMC505708127725766Panhuysen M., Vogt Weisenhorn D. M., Blanquet V., Brodski C., Heinzmann U., Beisker W., et al. (2004). Effects of Wnt1 signaling on proliferation in the developing mid-/hindbrain region. Mol. Cell. Neurosci. 26, 101–111. 10.1016/j.mcn.2004.01.01110.1016/j.mcn.2004.01.01115121182Pannese M., Polo C., Andreazzoli M., Vignali R., Kablar B., Barsacchi G., et al. (1995). The Xenopus homologue of Otx2 is a maternal homeobox gene that demarcates and specifies anterior body regions. Development 121, 707–720. 10.1242/dev.121.3.70710.1242/dev.121.3.7077720578Parr B. A., Shea M. J., Vassileva G., McMahon A. P. (1993). Mouse Wnt genes exhibit discrete domains of expression in the early embryonic CNS and limb buds. Development 119, 247–261. 10.1242/dev.119.1.24710.1242/dev.119.1.2478275860Parvin M. S., Okuyama N., Inoue F., Islam M. E., Kawakami A., Takeda H., et al. (2008). Autoregulatory loop and retinoic acid repression regulate pou2/pou5f1 gene expression in the zebrafish embryonic brain. Dev. Dyn. 237, 1373–1388. 10.1002/dvdy.2153910.1002/dvdy.2153918407549Patel N. H., Martin-Blanco E., Coleman K. G., Poole S. J., Ellis M. C., Kornberg T. B., et al. (1989). Expression of engrailed proteins in arthropods, annelids and chordates. Cell 58, 955–968. 10.1016/0092-8674(89)90947-110.1016/0092-8674(89)90947-12570637Pfeffer P. L., Bouchard M., Busslinger M. (2000). Pax2 and homeodomain proteins cooperatively regulate a 435 bp enhancer of the mouse Pax5 gene at the midbrain-hindbrain boundary. Development 127, 1017–1028. 10.1242/dev.127.5.101710.1242/dev.127.5.101710662641Pfeffer P. L., Gerster T., Lun K., Brand M., Busslinger M. (1998). Characterization of three novel members of the zebrafish Pax2/5/8 family: dependency of Pax5 and Pax8 expression on the Pax2.1 (noi) function. Development 125, 3063–3074. 10.1242/dev.125.16.306310.1242/dev.125.16.30639671580Pfeffer P. L., Payer B., Reim G., di Magliano M. P., Busslinger M. (2002). The activation and maintenance of Pax2 expression at the mid-hindbrain boundary is controlled by separate enhancers. Development 129, 307–318. 10.1242/dev.129.2.30710.1242/dev.129.2.30711807024Picker A., Brennan C., Reifers F., Clarke J. D., Holder N., Brand M. (1999). Requirement for the zebrafish mid-hindbrain boundary in midbrain polarisation, mapping and confinement of the retinotectal projection. Development 126, 2967–2978. 10.1242/dev.126.13.296710.1242/dev.126.13.296710357940Picker A., Scholpp S., Böhli H., Takeda H., Brand M. (2002). A novel positive transcriptional feedback loop in midbrain-hindbrain boundary development is revealed through analysis of the zebrafish pax2.1 promoter in transgenic lines. Development 129, 3227–3239. 10.1242/dev.129.13.322710.1242/dev.129.13.322712070097Pose-Méndez S., Candal E., Mazan S., Rodríguez-Moldes I. (2016). Genoarchitecture of the rostral hindbrain of a shark: basis for understanding the emergence of the cerebellum at the agnathan-gnathostome transition. Brain Struct. Funct. 221, 1321–1335. 10.1007/s00429-014-0973-810.1007/s00429-014-0973-825552316Puelles L. (2013). “Plan of the developing vertebrate nervous system relating embryology to the adult nervous system (prosomere model, overview of brain organization),” in Comprehensive Developmental Neuroscience: Patterning and Cell Type Specification in the Developing CNS and PNS, eds Rubenstein J. L. R., Rakic P. (Amsterdam: Academic Press; ), 187–209. 10.1016/B978-0-12-397265-1.00118-010.1016/B978-0-12-397265-1.00118-0Puelles L. (2018). Developmental studies of avian brain organization. Int. J. Dev. Biol. 62, 207–224. 10.1387/ijdb.170279LP10.1387/ijdb.170279LP29616730Puelles L., Ferran J. L. (2012). Concept of neural genoarchitecture and its genomic fundament. Front. Neuroanat. 6:47. 10.3389/fnana.2012.0004710.3389/fnana.2012.00047PMC349990223181010Puelles L., Harrison M., Paxinos G., Watson C. (2013). A developmental ontology for the mammalian brain based on the prosomeric model. Trends Neurosci. 36, 570–578. 10.1016/j.tins.2013.06.00410.1016/j.tins.2013.06.00423871546Puelles L., Martínez-de-la-Torre M., Paxinos G., Watson C., Martínez S. (2007). The Chick Brain in Stereotaxic Coordinates: An Atlas Featuring Neuromeric Subdivisions and Mammalian Homologies. San Diego, CA: Elsevier/Academic Press.Puelles L., Rubenstein J. L. R. (2003). Forebrain gene expression domains and the evolving prosomeric model. Trends Neurosci. 26, 469–476. 10.1016/S0166-2236(03)00234-010.1016/S0166-2236(03)00234-012948657Ramos-Mejía V., Escalante-Alcalde D., Kunath T., Ramírez L., Gertsenstein M., Nagy A., et al. (2005). Phenotypic analyses of mouse embryos with ubiquitous expression of Oct4: effects on mid-hindbrain patterning and gene expression. Dev. Dyn. 232, 180–190. 10.1002/dvdy.2021110.1002/dvdy.2021115580630Reifers F., Böhli H., Walsh E. C., Crossley P. H., Stainier D. Y., Brand M. (1998). Fgf8 is mutated in zebrafish acerebellar (ace) mutants and is required for maintenance of midbrain-hindbrain boundary development and somitogenesis. Development 125, 2381–2395. 10.1242/dev.125.13.238110.1242/dev.125.13.23819609821Reim G., Brand M. (2002). Spiel-ohne-grenzen/pou2 mediates regional competence to respond to Fgf8 during zebrafish early neural development. Development 129, 917–933. 10.1242/dev.129.4.91710.1242/dev.129.4.91711861475Rhinn M., Dierich A., le Meur M., Ang S. (1999). Cell autonomous and non-cell autonomous functions of Otx2 in patterning the rostral brain. Development 126, 4295–4304. 10.1242/dev.126.19.429510.1242/dev.126.19.429510477297Rhinn M., Dierich A., Shawlot W., Behringer R. R., le Meur M., Ang S. L. (1998). Sequential roles for Otx2 in visceral endoderm and neuroectoderm for forebrain and midbrain induction and specification. Development 125, 845–856. 10.1242/dev.125.5.84510.1242/dev.125.5.8459449667Rhinn M., Lun K., Ahrendt R., Geffarth M., Brand M. (2009). Zebrafish gbx1 refines the midbrain-hindbrain boundary border and mediates the Wnt8 posteriorization signal. Neural Dev. 4:12. 10.1186/1749-8104-4-1210.1186/1749-8104-4-12PMC267443919341460Rhinn M., Lun K., Amores A., Yan Y.-L., Postlethwait J. H., Brand M. (2003). Cloning, expression and relationship of zebrafish gbx1 and gbx2 genes to Fgf signaling. Mech. Dev. 120, 919–936. 10.1016/s0925-4773(03)00135-710.1016/s0925-4773(03)00135-712963112Rhinn M., Lun K., Luz M., Werner M., Brand M. (2005). Positioning of the midbrain-hindbrain boundary organizer through global posteriorization of the neuroectoderm mediated by Wnt8 signaling. Development 132, 1261–1272. 10.1242/dev.0168510.1242/dev.0168515703279Rhinn M., Lun K., Werner M., Simeone A., Brand M. (2004). Isolation and expression of the homeobox gene Gbx1 during mouse development. Dev. Dyn. 229, 334–339. 10.1002/dvdy.1043510.1002/dvdy.1043514745958Rifat Y., Parekh V., Wilanowski T., Hislop N. R., Auden A., Ting S. B., et al. (2010). Regional neural tube closure defined by the Grainy head-like transcription factors. Dev. Biol. 345, 237–245. 10.1016/j.ydbio.2010.07.01710.1016/j.ydbio.2010.07.01720654612Rijsewijk F., Schuermann M., Wagenaar E., Parren P., Weigel D., Nusse R. (1987). The Drosophila homology of the mouse mammary oncogene int-1 is identical to the segment polarity gene wingless. Cell 50, 649–657. 10.1016/0092-8674(87)90038-910.1016/0092-8674(87)90038-93111720Rohs P., Ebert A. M., Zuba A., McFarlane S. (2013). Neuronal expression of fibroblast growth factor receptors in zebrafish. Gene Expr. Patterns 13, 354–361. 10.1016/j.gep.2013.06.00610.1016/j.gep.2013.06.00623850987Rowitch D. H., Kispert A., McMahon A. P. (1999). Pax-2 regulatory sequences that direct transgene expression in the developing neural plate and external granule cell layer of the cerebellum. Dev. Brain Res. 117, 99–108. 10.1016/s0165-3806(99)00104-210.1016/s0165-3806(99)00104-210536237Rowitch D. H., McMahon A. P. (1995). Pax-2 expression in the murine neural plate precedes and encompasses the expression domains of Wnt-1 and En-1. Mech. Dev. 52, 3–8. 10.1016/0925-4773(95)00380-j10.1016/0925-4773(95)00380-j7577673Saarimäki-Vire J., Peltopuro P., Lahti L., Naserke T., Blak A. A., Weisenhorn D. M. V., et al. (2007). Fibrobast growth factor receptors cooperate to regulate neural progenitor properties in the developing midbrain and hindbrain. J. Neurosci. 27, 8581–8592. 10.1523/JNEUROSCI.0192-07.200710.1523/JNEUROSCI.0192-07.2007PMC667292917687036Sato T., Joyner A. L. (2009). The duration of. Fgf8isthmic organizer expression is key to patterning different tectal-isthmo-cerebellum structures. Development 136, 3617–3626. 10.1242/dev.04121010.1242/dev.041210PMC276111019793884Schier A. F., Neuhauss S. C. F., Harvey M., Malicki J., Solnica-Krezel L., Stainier D. Y. R., et al. (1996). Mutations affecting the development of the embryonic zebrafish brain. Development 123, 165–178. 10.1242/dev.123.1.16510.1242/dev.123.1.1659007238Scholpp S., Brand M. (2004). Zebrafish fgfr1 is a member of the fgf8 synexpression group and is required for fgf8 signalling at the midbrain-hindbrain boundary. Dev. Genes Evol. 214, 285–295. 10.1007/s00427-004-0409-110.1007/s00427-004-0409-115221377Schwarz M., Alvarez-Bolado G., Dressler G., Urbánek P., Busslinger M., Gruss P. (1999). Pax2/5 and Pax6 subdivide the early neural tube into three domains. Mech. Dev. 82, 29–39. 10.1016/s0925-4773(99)00005-210.1016/s0925-4773(99)00005-210354469Schwarz M., Alvarez-Bolado G., Urbánek P., Busslinger M., Gruss P. (1997). Conserved biological function between Pax-2 and Pax-5 in midbrain and cerebellum development: evidence from targeted mutations. Proc. Natl. Acad. Sci. U S A 94, 14518–14523. 10.1073/pnas.94.26.1451810.1073/pnas.94.26.14518PMC250409405645Sgado P., Alberi L., Gherbassi D., Galasso S. L., Ramakers G. M. J., Alavian K. N., et al. (2006). Slow progressive degeneration of nigral dopaminergic neurons in postnatal Engrailed mutant mice. Proc. Nat. Acad. Sci. U S A 103, 15242–15247. 10.1073/pnas.060211610310.1073/pnas.0602116103PMC162280717015829Sgaier S. K., Lao Z., Villanueva M. P., Berenshteyn F., Stephen D., Turnbull R. K., et al. (2007). Genetic subdivision of the tectum and cerebellum into functionally related regions based on differential sensitivity to engrailed proteins. Development 134, 2325–2335. 10.1242/dev.00062010.1242/dev.000620PMC284061317537797Shigetani Y., Funahashi J., Nakamura H. (1997). En-2 regulates the expression of the ligands for Eph type tyrosine kinases in chick embryonic tectum. Neurosci. Res. 27, 211–217. 10.1016/s0168-0102(96)01151-010.1016/s0168-0102(96)01151-09129179Shinga J., Itoh M., Shiokawa K., Taira S., Taira M. (2001). Early patterning of the prospective midbrain-hindbrain boundary by the HES-related gene XHR1 in Xenopus embryos. Mech. Dev 109, 225–239. 10.1016/s0925-4773(01)00528-710.1016/s0925-4773(01)00528-711731236Sieger D., Tautz D., Gajewski M. (2004). her11 is involved in the somitogenesis clock in zebrafish. Dev. Genes Evol. 214, 393–406. 10.1007/s00427-004-0427-z10.1007/s00427-004-0427-z15309634Simeone A., Acampora D., Mallamaci A., Stornaiuolo A., D’Apice M. R., Nigro V., et al. (1993). A vertebrate gene related to orthodenticle contains a homeodomain of the bicoid class and demarcates anterior neuroectoderm in the gastrulating mouse embryo. EMBO J. 12, 2735–2747.PMC4135248101484Simeone A., Puelles E., Acampora D. (2002). The Otx family. Curr. Opin. Genet. Dev. 12, 409–415. 10.1016/s0959-437x(02)00318-010.1016/s0959-437x(02)00318-012100885Simon H. H., Scholz C., O’Leary D. D. M. (2005). Engrailed genes control developmental fate of serotonergic and noradrenergic neurons in mid- and hindbrain in a gene dose-dependent manner. Mol. Cell Neurosci. 28, 96–105. 10.1016/j.mcn.2004.08.01610.1016/j.mcn.2004.08.01615607945Song D. L., Chalepakis G., Gruss P., Joyner A. L. (1996). Two Pax-binding sites are required for early embryonic brain expression of an Engrailed-2 transgene. Development 122, 627–635. 10.1242/dev.122.2.62710.1242/dev.122.2.6278625814Stoykova A., Gruss P. (1994). Roles of Pax-genes in developing and adult brain as suggested by expression patterns. J. Neurosci. 14, 1395–1412. 10.1523/JNEUROSCI.14-03-01395.199410.1523/JNEUROSCI.14-03-01395.1994PMC65775648126546Su C.-Y., Kemp H. A., Moens C. B. (2014). Cerebellar development in the absence of Gbx function in zebrafish. Dev. Biol. 386, 181–190. 10.1016/j.ydbio.2013.10.02610.1016/j.ydbio.2013.10.026PMC393551024183937Su Y., Meng A. (2002). The expression of gbx-2 during zebrafish embryogenesis. Mech. Dev. 113, 107–110. 10.1016/s0925-4773(02)00011-410.1016/s0925-4773(02)00011-411900984Suda Y., Matsuo I., Aizawa S. (1997). Cooperation between Otx1 and Otx2 genes in developmental patterning of rostral brain. Mech. Dev. 69, 125–141. 10.1016/s0925-4773(97)00161-510.1016/s0925-4773(97)00161-59486536Sugiyama S., Funahashi J., Kitajewski J., Nakamura H. (1998). Crossregulation between En-2 and Wnt-1 in chick tectal development. Dev. Growth Differ. 40, 157–166. 10.1046/j.1440-169x.1998.00005.x10.1046/j.1440-169x.1998.00005.x9572358Sun X., Meyers E. N., Lewandoski M., Martin G. R. (1999). Targeted disruption of Fgf8 causes failure of cell migration in the gastrulating mouse embryo. Genes Dev. 13, 1834–1846. 10.1101/gad.13.14.183410.1101/gad.13.14.1834PMC31688710421635Sunmonu N. A., Chen L., Li J. Y. H. (2009). Misexpression of Gbx2 throughout the mesencephalon by a conditional gain-of-function transgene leads to deletion of the midbrain and cerebellum in mice. Genesis 47, 667–673. 10.1002/dvg.2054610.1002/dvg.20546PMC278358819603509Sunmonu N. A., Li K., Guo Q., Li J. Y. H. (2011). Gbx2 and Fgf8 are sequentially required for formation of the midbrain-hindbrain compartment boundary. Development 138, 725–734. 10.1242/dev.05566510.1242/dev.055665PMC302641621266408Takada H., Hattori D., Kitayama A., Ueno N., Taira M. (2005). Identification of target genes for the Xenopus Hes-related protein XHR1, a prepattern factor specifying the midbrain-hindbrain boundary. Dev. Biol. 283, 253–267. 10.1016/j.ydbio.2005.04.02010.1016/j.ydbio.2005.04.02015935340Takahashi N., Tochimoto N., Ohmori S. Y., Mamada H., Itoh M., Inamori M., et al. (2005). Systematic screening for genes specifically expressed in the anterior neuroectoderm during early Xenopus development. Int. J. Dev. Biol. 49, 939–951. 10.1387/ijdb.052083nt10.1387/ijdb.052083nt16281171Tallafuß A., Bally-Cuif L. (2003). Tracing of her5 progeny in zebrafish transgenics reveals the dynamics of midbrain-hindbrain neurogenesis and maintenance. Development 130, 4307–4323. 10.1242/dev.0066210.1242/dev.0066212900448Tallafuß A., Wilm T. P., Crozatier M., Pfeffer P., Wassef M., Bally-Cuif L. (2001). The zebrafish buttonhead-like factor Bts1 is an early regulator of pax2.1 expression during mid-hindbrain development. Development 128, 4021–4034. 10.1242/dev.128.20.402110.1242/dev.128.20.402111641225Tanaka A., Miyamoto K., Minamino N., Takeda M., Sato B., Matsuo H., et al. (1992). Cloning and characterization of an androgen-induced growth factor essential for the androgen-dependent growth of mouse mammary carcinoma cells. Proc. Natl. Acad. Sci. U S A 89, 8928–8932. 10.1073/pnas.89.19.892810.1073/pnas.89.19.8928PMC500371409588Thawani A., Groves A. K. (2020). Building the border: development of the chordate neural plate border region and its derivatives. Front. Physiol. 11:608880. 10.3389/fphys.2020.60888010.3389/fphys.2020.608880PMC775046933364980Thomas K. R., Capecchi M. R. (1990). Targeted disruption of the murine int-1 proto-oncogene resulting in severe abnormalities in midbrain and cerebellar development. Nature 346, 847–850. 10.1038/346847a010.1038/346847a02202907Thomas K. R., Musci T. S., Neumann P. E., Capecchi M. R. (1991). Swaying is a mutant allele of the proto-oncogene Wnt-1. Cell 67, 969–976. 10.1016/0092-8674(91)90369-a10.1016/0092-8674(91)90369-a1835670Tossell K., Andreae L. C., Cudmore C., Lang E., Muthukrishnan U., Lumsden A., et al. (2011a). Lrrn1 is required for formation of the midbrain-hindbrain boundary and organiser through regulation of affinity differences between midbrain and hindbrain cells in chick. Dev. Biol. 352, 341–352. 10.1016/j.ydbio.2011.02.00210.1016/j.ydbio.2011.02.002PMC308445621315708Tossell K., Kiecker C., Wizenmann A., Lang E., Irving C. (2011b). Notch signalling stabilises boundary formation at the midbrain-hindbrain organiser. Development 138, 3745–3757. 10.1242/dev.07031810.1242/dev.070318PMC315292821795283Tour E., Pillemer G., Gruenbaum Y., Fainsod A. (2001). The two Xenopus Gbx2 genes exhibit similar, but not identical expression patterns and can affect head formation. FEBS Lett. 507, 205–209. 10.1016/s0014-5793(01)02963-510.1016/s0014-5793(01)02963-511684099Tour E., Pillemer G., Gruenbaum Y., Fainsod A. (2002a). Gbx2 interacts with Otx2 and patterns the anterior-posterior axis during gastrulation in Xenopus. Mech. Dev. 112, 141–151. 10.1016/s0925-4773(01)00653-010.1016/s0925-4773(01)00653-011850185Tour E., Pillemer G., Gruenbaum Y., Fainsod A. (2002b). Otx2 can activate the isthmic organizer genetic network in the Xenopus embryo. Mech. Dev. 110, 3–13. 10.1016/s0925-4773(01)00591-310.1016/s0925-4773(01)00591-311744364Trokovic R., Jukkola T., Saarimäki J., Peltopuro P., Naserke T., Weisenhorn D. M. V., et al. (2005). Fgfr1-dependent boundary cells between developing mid- and hindbrain. Dev. Biol. 278, 428–439. 10.1016/j.ydbio.2004.11.02410.1016/j.ydbio.2004.11.02415680361Trokovic R., Trokovic N., Hernesniemi S., Pirvola U., Weisenhorn D. M. V., Rossant J., et al. (2003). FGFR1 in independently required in both developing mid- and hindbrain for sustained response to isthmic signals. EMBO J. 22, 1822–1823. 10.1093/emboj/cdg16910.1093/emboj/cdg169PMC15446112682014Tsuda S., Hiyoshi K., Miyazawa H., Kinno R., Yamasu K. (2019). 4D imaging identifies dynamic migration and the fate of gbx2-expressing cells in the brain primordium of zebrafish. Neurosci. Lett. 690, 112–119. 10.1016/j.neulet.2018.09.02710.1016/j.neulet.2018.09.02730222999Urbánek P., Fetka I., Meisler M. H., Busslinger M. (1997). Cooperation of Pax2 and Pax5 in midbrain and cerebellum development. Proc. Natl. Acad. Sci. U S A 94, 5703–5708. 10.1073/pnas.94.11.570310.1073/pnas.94.11.5703PMC208429159136Urbánek P., Wang Z. Q., Fetka I., Wagner E. F., Busslinger M. (1994). Complete block of early B cell differentiation and altered patterning of the posterior midbrain in mice lacking Pax5/BSAP. Cell 79, 901–912. 10.1016/0092-8674(94)90079-510.1016/0092-8674(94)90079-58001127Vaage S. (1969). The segmentation of the primitive neural tube in chick embryos (Gallus domesticus). A morphological, histochemical and autoradiographical investigation. Ergeb. Anat. Entwicklungsgesch. 41, 3–87. 5363604Vieira C., Pombero A., Garcia-Lopez R., Gimeno L., Echevarria D., Martinez S. (2010). Molecular mechanisms controlling brain development: an overview of neuroepithelial secondary organizers. Int. J. Dev. Biol. 54, 7–20. 10.1387/ijdb.092853cv10.1387/ijdb.092853cv19876817von Bubnoff A., Schmidt J. E., Kimelman D. (1996). The Xenopus laevis homeobox gene Xgbx-2 is an early marker of anteroposterior patterning in the ectoderm. Mech. Dev. 54, 149–160. 10.1016/0925-4773(95)00468-810.1016/0925-4773(95)00468-88652408Walshe J., Mason I. (2000). Expression of FGFR1, FGFR2 and FGFR3 during early neural development in the chick embryo. Mech. Dev. 90, 103–110. 10.1016/s0925-4773(99)00225-710.1016/s0925-4773(99)00225-710585567Wassarman K. M., Lewandoski M., Campbell K., Joyner A. L., Rubenstein J. L., Martinez S., et al. (1997). Specification of the anterior hindbrain and establishment of a normal mid/hindbrain organizer is dependent on Gbx2 gene function. Development 124, 2923–2934. 10.1242/dev.124.15.292310.1242/dev.124.15.29239247335Waters S. T., Lewandoski M. (2006). A threshold requirement for Gbx2 levels in hindbrain development. Development 133, 1991–2000. 10.1242/dev.0236410.1242/dev.0236416651541Watson C., Shimogori T., Puelles L. (2017). Mouse Fgf8-Cre-LacZ lineage analysis defines the territory of the postnatal mammalian isthmus. J. Comp. Neurol. 525, 2782–2799. 10.1002/cne.2424210.1002/cne.2424228510270Webb K. J., Coolen M., Gloeckner C. J., Stigloher C., Bahn B., Topp S., et al. (2011). The Enhancer of split transcription factor Her8a is a novel dimerisation partner for Her3 that controls anterior hindbrain neurogenesis in zebrafish. BMC Dev. Biol. 11:27. 10.1186/1471-213X-11-2710.1186/1471-213X-11-27PMC312527021586122Wilanowski T., Tuckfield A., Cerruti L., O’Connell S., Saint R., Parekh V., et al. (2002). A highly conserved novel family of mammalian developmental transcription factors related to Drosophila grainyhead. Mech. Dev. 114, 37–50. 10.1016/s0925-4773(02)00046-110.1016/s0925-4773(02)00046-112175488Wilkinson D. G., Bailes J. A., McMahon A. P. (1987). Expression of the proto-oncogene int-1 is restricted to specific neural cells in the developing mouse embryo. Cell 50, 79–88. 10.1016/0092-8674(87)90664-710.1016/0092-8674(87)90664-73594565Wolda S. L., Moody C. J., Moon R. T. (1993). Overlapping expression of Xwnt-3A and Xwnt-1 in neural tissue of Xenopus laevis embryos. Dev. Biol. 155, 46–57. 10.1006/dbio.1993.100510.1006/dbio.1993.10058416844Wurst W., Auerbach A. B., Joyner A. L. (1994). Multiple developmental defects in Engrailed-1 mutant mice: an early mid-hindbrain deletion and patterning defects in forelimbs and sternum. Development 120, 2065–2075. 10.1242/dev.120.7.206510.1242/dev.120.7.20657925010Yamaguchi T. P., Conlon R. A., Rossant J. (1992). Expression of the fibroblast growth factor receptor FGFR-1/flg during gastrulation and segmentation in the mouse embryo. Dev. Biol 152, 75–88. 10.1016/0012-1606(92)90157-c10.1016/0012-1606(92)90157-c1321062Ye W., Bouchard M., Stone D., Liu X., Vella F., Lee J., et al. (2001). Distinct regulators control the expression of the mid-hindbrain organizer signal FGF8. Nat. Neurosci. 4, 1175–1181. 10.1038/nn76110.1038/nn76111704761Zervas M., Millet S., Ahn S., Joyner A. L. (2004). Cell behaviors and genetic lineages of the mesencephalon and rhombomere 1. Neuron 43, 345–357. 10.1016/j.neuron.2004.07.01010.1016/j.neuron.2004.07.01015294143