Regulatory Elements, Protein Function and Evolution of the Actinodin Genes

Small fibrils termed actinotrichia are involved with the growth and structure of the fin fold during fin development in fish. The actinodin (and) genes are required for actinotrichia formation, and the loss of these genes from the genomes of tetrapods has been implicated in the tetrapod-specific loss of actinotrichia, loss of a fin fold and the concurrent evolution of paired fins into limbs. This study focuses on the function of the and genes and their role in actinotrichia formation. The results reveal cis-acting regulatory elements required for and1 expression in the fin epithelium. Furthermore, it is shown that the And proteins display similarities to the secreted signaling molecule, Ecrg4, implying a possible role in cell differentiation during fin fold development. In the final section of this report, I use a genomic analysis to show that the and genes were lost from otherwise well-conserved syntenic loci in fish and tetrapod genomes. These results suggest possible causes for the evolutionary loss of and genes and the associated developmental changes that may have permitted fin to limb evolution