title: The dlx5a/dlx6a genes play essential roles in the early development of zebrafish median fin and pectoral structures.
abstract: The Dlx5 and Dlx6 genes encode homeodomain transcription factors essential for the proper development of limbs in mammalian species. However, the role of their teleost counterparts in fin development has received little attention. Here, we show that dlx5a is an early marker of apical ectodermal cells of the pectoral fin buds and of the median fin fold, but also of cleithrum precursor cells during pectoral girdle development. We propose that early median fin fold establishment results from the medial convergence of dlx5a-expressing cells at the lateral edges of the neural keel. Expression analysis also shows involvement of dlx5a during appendage skeletogenesis. Using morpholino-mediated knock down, we demonstrate that disrupted dlx5a/6a function results in pectoral fin agenesis associated with misexpression of bmp4, fgf8a, and1 and msx genes. In contrast, the median fin fold presents defects in mesenchymal cell migration and actinotrichia formation, whereas the initial specification seems to occur normally. Our results demonstrate that the dlx5a/6a genes are essential for the induction of pectoral fin outgrowth, but are not required during median fin fold specification. The dlx5a/6a knock down also causes a failure of cleithrum formation associated with a drastic loss of runx2b and col10a1 expression. The data indicate distinct requirements for dlx5a/6a during median and pectoral fin development suggesting that initiation of unpaired and paired fin formation are not directed through the same molecular mechanisms. Our results refocus arguments on the mechanistic basis of paired appendage genesis during vertebrate evolution.
authors.affiliation: Centre for Advanced Research in Environmental Genomics, Department of Biology, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Eglantine
authors.initials: E
authors.lastname: Heude
authors.affiliation: Centre for Advanced Research in Environmental Genomics, Department of Biology, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Sarah
authors.initials: S
authors.lastname: Shaikho
authors.affiliation: Centre for Advanced Research in Environmental Genomics, Department of Biology, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Marc
authors.initials: M
authors.lastname: Ekker
mesh_terms: D058500:Animal Fins / Q000196:embryology*; D000818:Animals; D002465:Cell Movement / Q000502:physiology; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D055785:Gene Knockdown Techniques; D018398:Homeodomain Proteins / Q000096:biosynthesis* / Q000235:genetics; D008648:Mesoderm / Q000196:embryology; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics; D029961:Zebrafish Proteins / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D018398:Homeodomain Proteins; D014157:Transcription Factors; D029961:Zebrafish Proteins; C501122:dlx5a protein, zebrafish; C491015:dlx6a protein, zebrafish