Morphogenesis and evolution of vertebrate appendicular muscle formation

In vertebrate evolution the advent of terrestrial tetrapod species resulted in a shift in locomotor strategies. Although the fossil record gives some understanding as to how the appendicular skeleton of the fin has evolved into limbs it provides little insight into how these muscles arose. This study is specifically concerned with determining how the muscles of the fins and limbs have evolved within the vertebrate lineage. Neyt et al., 2000, Haines and Currie 2001 previously defined both primitive and derived modes of fin and limb muscle formation. We aim to generate a detailed understanding of the morphological and genetic basis for these two different morphologies. Previous analysis relates specifically to muscle formation in the pectoral fin (forerunner of the tetrapod forelimb). Almost no information exists as to the nature of muscle formation in the pelvic fin (forerunner to hindlimb). This is a matter of some importance as it is well characterised that fore and hind limbs in amniote species both utilise the same derived mechanism of LBX positive, mesenchymal migratory myoblasts to generate limb musculature. We have examined the mechanisms that are utilised to generate muscle formation within the paired fins of zebrafish and phylogenetically diverse range of vertebrate species Our initial observations suggest some differences between pectoral and pelvic fin muscle formation pointing to the potential importance of pelvic fin muscle evolution for the tetrapod transition on to land.