MEDLER, S; CHANG, ES; MYKLES, DL; Colorado State University; Bodega Marine Lab; Colorado State University: Myofibrillar gene expression in lobster skeletal muscles

Skeletal muscle fibers of crustaceans exhibit diversity in myofibrillar assemblage, similar to fibers from mammals and other animals. For example, lobster (Homarus americanus) fast fibers express fast myosin heavy chain (MHC), P75, and troponin T ₂; while lobster slow phasic fibers express slow MHC, troponin T ₃, but not P75. Such isoform assemblages combined with structural and physiological data have defined lobster muscles as fast, slow phasic (S₁), or slow tonic (S₂). The objective of the current study was to further define differences among fiber types in terms of MHC distribution and expression in various muscles. Distinct MHCs were identified using SDS-PAGE and Western blotting techniques. The results demonstrated that most MHC proteins have similar mobility on high-resolution SDS PAGE gels, with the exception of an MHC found in S₂ fibers. In complementary analyses, partial clones for MHC from deep abdominal flexor (fast), crusher claw closer (slow), and P75 were used to design fiber-specific primers for RT-PCR and real-time PCR. These analyses revealed distinct expression patterns among the various fiber types. Fast and slow claw fibers expressed low levels of the alternate MHC (i.e., slow MHC in fast fibers and fast MHC in slow fibers), whereas deep abdominal flexor muscle expressed only the fast isoform. In addition, there was a significant correlation between slow MHC and actin expression, with slow fibers expressing greater levels of actin. These techniques are now being used to measure myofibrillar gene expression in muscles from juvenile claws at different molt stages and in muscles from ecdysteroid-treated animals. Supported by NSF (IBN-0077422) and NIH (AR 08597-01A1).