Meeting Abstract
The formation of a functionally integrated musculoskeletal system is one of the fundamental aspects of vertebrate development. In mouse and chick model systems, much work has been done to characterize the formation of appendicular musculature. These studies demonstrate that myogenic precursor cells express the transcription factor Pax3 and its downstream targets Lbx1 and c-MET, delaminate from pectoral and pelvic level somites, and undergo a long range migration into the limb buds where they mix with lateral plate derived connective tissue. Once in the limb buds, these muscle precursor cells upregulate the myogenic regulatory factors MyoD and Myf5, and differentiate into mature myofibers. Notably, a migratory mode of muscle formation has been demonstrated during paired fin formation in teleosts, and appears to be a conserved feature of osteichthyans. Median fins predate the appearance of paired fins in the fossil record, and in extant taxa express many of the same genes that pattern limb buds. Together, these paleontological and molecular data have fueled the hypothesis that the early evolution of paired fins involved the redeployment of pre-existing developmental programs from the midline to the flank. Here we use antibody labeling and in-situ hybridization to characterize the expression of Pax3/Pax7, Lbx1, c-MET, and myogenic regulatory factors during muscle formation in the paired and unpaired fins of the American paddlefish Polyodon spathula, a basal actinopterygian. We use these data to generate new hypotheses about the conserved, core genetic machinery underlying appendage muscularization in vertebrates and discuss potential avenues of future investigation to test these hypotheses.
