title: Zebrafish msxB, msxC and msxE function together to refine the neural-nonneural border and regulate cranial placodes and neural crest development.
abstract: The zebrafish muscle segment homeobox genes msxB, msxC and msxE are expressed in partially overlapping domains in the neural crest and preplacodal ectoderm. We examined the roles of these msx genes in early development. Disrupting individual msx genes causes modest variable defects, whereas disrupting all three produces a reproducible severe phenotype, suggesting functional redundancy. Neural crest differentiation is blocked at an early stage. Preplacodal development begins normally, but placodes arising from the msx expression domain later show elevated apoptosis and are reduced in size. Cell proliferation is normal in these tissues. Unexpectedly, Msx-deficient embryos become ventralized by late gastrulation whereas misexpression of msxB dorsalizes the embryo. These effects appear to involve Distal-less (Dlx) protein activity, as loss of dlx3b and dlx4b suppresses ventralization in Msx-depleted embryos. At the same time, Msx-depletion restores normal preplacodal gene expression to dlx3b-dlx4b mutants. These data suggest that mutual antagonism between Msx and Dlx proteins achieves a balance of function required for normal preplacodal differentiation and placement of the neural-nonneural border.
authors.affiliation: Biology Department, Texas A and M University, College Station, TX 77843-3258, USA.
authors.forename: Bryan T
authors.initials: BT
authors.lastname: Phillips
authors.forename: Hye-Joo
authors.initials: HJ
authors.lastname: Kwon
authors.forename: Colt
authors.initials: C
authors.lastname: Melton
authors.forename: Paul
authors.initials: P
authors.lastname: Houghtaling
authors.forename: Andreas
authors.initials: A
authors.lastname: Fritz
authors.forename: Bruce B
authors.initials: BB
authors.lastname: Riley
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D002470:Cell Survival; D004625:Embryo, Nonmammalian / Q000033:anatomy & histology / Q000502:physiology; D004628:Embryonic Structures / Q000033:anatomy & histology / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D017403:In Situ Hybridization; D009432:Neural Crest / Q000166:cytology / Q000196:embryology*; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D016376:Oligonucleotides, Antisense / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C088334:Distal-less homeobox proteins; D018398:Homeodomain Proteins; D016376:Oligonucleotides, Antisense; D014157:Transcription Factors; D029961:Zebrafish Proteins; C513489:msx1a protein, zebrafish; C460082:msx1b protein, zebrafish; C513488:msx3 protein, zebrafish