THOMPSON, M.D.*; KIM, H.-W.; MYKLES, D.L.; Colorado State University; Colorado State University; Colorado State University: Expression of Troponin-C Isoforms in Lobster Skeletal Muscle

Troponin-C (TnC) is a calcium-binding subunit of the heterotrimeric troponin complex that mediates calcium-dependent contraction in skeletal muscle. Isoforms are differentially expressed in fast and slow skeletal muscles of American lobster, Homarus americanus. In juveniles, fiber-type switching occurs as claws differentiate into the cutter and crusher types. This requires differential expression and/or mRNA processing of genes encoding TnC and other myofibrillar proteins. In adults, claw muscles undergo a molt-induced atrophy to facilitate withdrawal of the claw at ecdysis. Isoformic expression can be used as a marker for changes in gene regulation/expression associated with fiber-type switching and muscle atrophy. A full-length cDNA encoding a fast isoform of TnC was cloned from deep abdominal muscle. The deduced amino acid sequence is different from those of three known lobster TnC isoforms. Thus, there are at least four TnC isoforms. RT-PCR showed that TnC is expressed in skeletal muscle. Currently, variations on the 3� RACE technique are being employed on RNA isolated from different muscle types during development. Our goal is to establish what isoforms are present, where they are expressed, and how they are regulated during muscle atrophy and fiber-type switching. Supported by NSF (IBN 00-77422).