THOMPSON, M.D.; KIM, H.-W.; MYKLES, D.L.: Characterization of a cDNA encoding lobster muscle troponin-C

Troponin-C (TnC) is the calcium-binding subunit of the heterotrimeric troponin complex that mediates calcium-dependent contraction in skeletal muscle. Three 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. A cDNA encoding a full-length sequence of TnC was cloned from a lobster fast muscle library. The deduced amino acid sequence (150 residues; about 17 kDa) showed high identity to other TnC sequences, but the DNA sequence was less conserved due to codon degeneracy and alternative codon usage. In continuing work, we are examining the expression of TnC in different tissues, as well as in claw muscle at different stages of the intermolt cycle and during development. Our goal is to characterize cDNAs encoding the other two isoforms to study the regulation of TnC expression during muscle atrophy and fiber-type switching. Supported by NSF (IBN-0077422).