title: Differential actinodin1 regulation in zebrafish and mouse appendages.
abstract: The fin-to-limb transition is an important evolutionary step in the colonization of land and diversification of all terrestrial vertebrates. We previously identified a gene family in zebrafish, termed actinodin, which codes for structural proteins crucial for the formation of actinotrichia, rigid fibrils of the teleost fin. Interestingly, this gene family is absent from all tetrapod genomes examined to date, suggesting that it was lost during limb evolution. To shed light on the disappearance of this gene family, and the consequences on fin-to-limb transition, we characterized actinodin regulatory elements. Using fluorescent reporters in transgenic zebrafish, we identified tissue-specific cis-acting regulatory elements responsible for actinodin1 (and1) expression in the ectodermal and mesenchymal cell populations of the fins, respectively. Mutagenesis of potential transcription factor binding sites led to the identification of one binding site crucial for and1 expression in ectodermal cells. We show that these regulatory elements are partially functional in mouse limb buds in a tissue-specific manner. Indeed, the zebrafish regulatory elements target expression to the dorsal and ventral ectoderm of mouse limb buds. Absence of expression in the apical ectodermal ridge is observed in both mouse and zebrafish. However, cells of the mouse limb bud mesoderm do not express the transgene, in contrast to zebrafish. Altogether these results hint for a change in regulation of and1 during evolution that led to the downregulation and eventual loss of this gene from tetrapod genomes.
authors.affiliation: Centre for Advanced Research in Environmental Genomics, University of Ottawa, 20 Marie-Curie, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: R L
authors.initials: RL
authors.lastname: Lalonde
authors.affiliation: McGill University and GQ Innovation Centre, Department of Anatomy and Cell Biology, McGill University, 740 Avenue du Docteur-Penfield, Montréal, Québec, Canada H3A 0G1.
authors.forename: D
authors.initials: D
authors.lastname: Moses
authors.affiliation: Centre for Advanced Research in Environmental Genomics, University of Ottawa, 20 Marie-Curie, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Centre for Advanced Research in Environmental Genomics, University of Ottawa, 20 Marie-Curie, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: N
authors.initials: N
authors.lastname: Cornell
authors.affiliation: Centre for Advanced Research in Environmental Genomics, University of Ottawa, 20 Marie-Curie, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: M
authors.initials: M
authors.lastname: Ekker
authors.affiliation: Centre for Advanced Research in Environmental Genomics, University of Ottawa, 20 Marie-Curie, Ottawa, Ontario, Canada K1N 6N5. Electronic address: makimenko@uottawa.ca.
authors.forename: M-A
authors.initials: MA
authors.lastname: Akimenko
mesh_terms: D058500:Animal Fins / Q000196:embryology* / Q000378:metabolism; D000818:Animals; D030801:Animals, Genetically Modified; D001665:Binding Sites / Q000235:genetics; D005075:Biological Evolution; D005121:Extremities / Q000196:embryology* / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D018878:Limb Buds / Q000254:growth & development / Q000378:metabolism; D008648:Mesoderm / Q000166:cytology*; D051379:Mice; D009024:Morphogenesis / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins / Q000235:genetics*
chemical_list: D029961:Zebrafish Proteins; C551359:actinodin 1, zebrafish