Meeting Abstract

93.3  Saturday, Jan. 7  Nuclear distribution in skeletal muscle of selected members of Chondrichthyes PRIESTER, C*; CORNELISSEN, A; KINSEY, S; DILLAMAN, R; University of North Carolina Wilmington

Mammalian muscle is characterized by fibers (cells) typically <100 µm in diameter and containing multiple nuclei located just under the sarcolemma. As animals grow, new fibers with the same nuclear organization are added (hyperplasic growth). Fibers can also increase in size (hypertrophic growth), reaching very large sizes in some animals. This occurs in white muscle of crustaceans where fibers may increase in diameter from <50 to >400 µm. In response to increases in diffusion distances during hypertrophic growth there are shifts in the distributions of mitochondria and nuclei. Mitochondria are evenly distributed across the fiber in small fibers, but are predominately peripheral (subsarcolemmal or SS) in large fibers; whereas nuclei are predominately SS in small fibers but are more centrally located (intermyofibrillar or IM) in large fibers. We have seen a similar pattern in the teleost Centropristis striata. Here we expanded this investigation to include representatives from a primitive class of fishes, the Chondrichthyes. Red and white fibers were identified and mitochondrial distribution was determined by SDH staining. Ratfish white fibers had mostly SS but also IM nuclei in all fish sizes examined. However, representative sharks and rays had red fibers resembling mammalian fibers, but their white fibers, even small ones, had predominantly IM nuclei, suggesting their red and white fibers anchor nuclei using different proteins. Furthermore, the location of nuclei in all species examined to date appears to be associated with microtubules (MT’s) that form bundles found throughout the cytoplasm. The MT’s are predominantly oriented parallel to the myofibrils and with perpendicular branches. They also often form “baskets” around both IM and SS nuclei, suggesting an anchoring role.