DAVIS, M.C.*; DAHN, R.D.; SHUBIN, N.H.; University of Chicago; University of Chicago; University of Chicago: Gene expression and function in the paired fins of basal actinopterygians

Comparative studies of fins and limbs reveal a high degree of conservation in the genetic pathways present. However, there are significant differences in the patterns of gene expression observed that may underlie the fundamentally different appendage skeletons found in tetrapods and zebrafish. At issue is whether the characteristics ways in which tetrapod and teleost appendages develop represent derived conditions specific to each group or are the result of retention of ancient and generalized appendage patterning mechanisms. To address this question, we examined the expression patterns of key appendage patterning genes in the phylogenetically basal actinopterygians Polyodon spathula and Lepisosteus osseus , which retain the primitive vertebrate paired fin pattern and, thus, possess skeletal elements homologous to both zebrafish fin radials and tetrapod limb bones. Genes examined in this study include a number of genes that have been identified as important regulators of appendage patterning in vertebrate model systems, yet exhibit significant differences in their expression in tetrapods and teleosts. To further understand the regulation of appendage patterning in basal actinopterygians, we also examined the functional roles of several genes that play a role in appendage patterning using pharmacological mutagens. In particular, exposure to the posterior agent retinoic acid provided a number of insights into the regulation of the anterior-posterior axis in developing paired and unpaired fins.