Meeting Abstract
P2.101 Wednesday, Jan. 5 Masticatory Myosin Expression in Jaw Adductor Muscles of the Ghost Shark, Callorhynchus callorhinchus REISER, P.J.*; FERRY, L.A.; Ohio State University; Arizona State University reiser.17@osu.edu
Holocephalans were probably the dominant hard prey specialists (i.e., durophagous) of the late Paleozoic, and are uniquely derived in this aspect. The upper jaw is fused to the neurocranium, a condition derived from a non-fused ancestor. Further, all chimaeriform holocephalans possess(ed) tooth plates, considered to be specialized for durophagy. Bite force was estimated previously from anatomical data for Callorhynchus callorhinchus, Hydrolagus collei, and Chimaera monstrosa (Ferry et al.; SICB 2010). Contrary to predictions in the literature, bite force estimates did not suggest that there are notable performance differences among these species. Further, CT scans suggested only very subtle differences in the amount of skeletal calcification between Callorhynchus and Hydrolagus. However, muscle fiber type differences were noted: Callorhynchus seemed to have an unusual mixture of red and white fibers in the jaw adductors. This prompted the study of myosin isoforms in Callorhynchus jaw adductor muscles. SDS-PAGE and immunoblotting with an anti-masticatory myosin heavy chain (MHC) antibody (anti-MHC-M) were used to probe homogenates of jaw adductor, epaxial and pectoral fin muscles. Jaw adductors have a major MHC isoform that is not present in the epaxial muscle or fin muscle, plus two other much less abundant MHC isoforms. Anti-MHC-M reacted strongly with jaw-adductor samples but did not react with epaxial or fin muscles. Consistent with other vertebrate species that express MHC-M, the predominant myosin light chain isoforms in jaw-adductor muscles also appear to be unique, differing from those in epaxial and fin muscles. We conclude that C. callorhinchus jaw adductors express masticatory myosin which, in several other vertebrate species, is associated with high unusually force generation.
