SCHACHAT, F*; SONG, L; LONG, JR., JH; KOOB, TJ; Duke University; Duke University; Vassar College; Shriners Hospital for Children, Tampa: Specialized Muscle in the Skate Embryonic Tail Appendage Enables Perfusion

Fertilized eggs of the North Atlantic little skate, Leucoraja erinacea, are laid in a horny capsule that protects the embryo from predators. At the same time, the capsule severely limits the exchange of dissolved gases. To obtain sufficient oxygen during the last two third of development, the embryo propels sea water through small slits that form in the outer edge of the four horns on the capsule’s periphery. This ventilation is accomplished by steady undulatory flexures of a caudal extension of the embyro’s tail. Because the embryonic tail appendage disappears after hatching, we predict that it expresses contractile proteins specific for its specialized function. We compared the myosin heavy chains (MYHs) of embryonic axial musculature from the pectoral fin, the non-undulatory portion of the embryonic tail, and the caudal-most tail appendage. MYHs were separated by SDS-PAGE and characterized by MALDI-TOF peptide mass fingerprinting of tryptic fragments. This proteomic analysis revealed physiological differences in myosin expression: the peptide map of the tail appendage MYH indicates it is similar to slow myosin, while the two myosins prevalent in the pectoral fin and rostral tail musculature are more like fast myosins. The expression of a slow-type MYH in the embryonic tail appendage is consistent with its nearly continuous, fatigue-resistant activity. Interestingly, the MYHs expressed in the embryonic muscles studied differ from the predominant MYH in adult skate pectoral fin muscle, suggesting that developmental MYH isoforms analogous to those found in birds and mammals are also expressed in elasmobranch axial musculature during embryonic development.