Loss of fish actinotrichia proteins and the fin-to-limb transition

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Item Type:	Article
Title:	Loss of fish actinotrichia proteins and the fin-to-limb transition
Creators Name:	Zhang, J., Wagh, P., Guay, D., Sanchez-Pulido, L., Padhi, B.K., Korzh, V., Andrade-Navarro, M.A. and Akimenko, M.A.
Abstract:	The early development of teleost paired fins is strikingly similar to that of tetrapod limb buds and is controlled by similar mechanisms. One early morphological divergence between pectoral fins and limbs is in the fate of the apical ectodermal ridge (AER), the distal epidermis that rims the bud. Whereas the AER of tetrapods regresses after specification of the skeletal progenitors, the AER of teleost fishes forms a fold that elongates. Formation of the fin fold is accompanied by the synthesis of two rows of rigid, unmineralized fibrils called actinotrichia, which keep the fold straight and guide the migration of mesenchymal cells within the fold. The actinotrichia are made of elastoidin, the components of which, apart from collagen, are unknown. Here we show that two zebrafish proteins, which we name actinodin 1 and 2 (And1 and And2), are essential structural components of elastoidin. The presence of actinodin sequences in several teleost fishes and in the elephant shark (Callorhinchus milii, which occupies a basal phylogenetic position), but not in tetrapods, suggests that these genes have been lost during tetrapod species evolution. Double gene knockdown of and1 and and2 in zebrafish embryos results in the absence of actinotrichia and impaired fin folds. Gene expression profiles in embryos lacking and1 and and2 function are consistent with pectoral fin truncation and may offer a potential explanation for the polydactyly observed in early tetrapod fossils. We propose that the loss of both actinodins and actinotrichia during evolution may have led to the loss of lepidotrichia and may have contributed to the fin-to-limb transition.
Keywords:	Animal Structures, Biological Models, Collagen, Developmental Gene Expression Regulation, Ectoderm, Evolution, Extremities, Fish Proteins, Gene Expression Profiling, Gene Knockdown Techniques, Limb Buds, Molecular Evolution, Nonmammalian Embryo, Phylogeny, Animals, Zebrafish
Source:	Nature
ISSN:	0028-0836
Publisher:	Nature Publishing Group
Volume:	466
Number:	7303
Page Range:	234-237
Date:	8 July 2010
Official Publication:	https://doi.org/10.1038/nature09137
PubMed:	View item in PubMed

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