LILLEY, T.L.; MEDLER, S.; MYKLES, D.L.; Colorado State University; Colorado State University; Colorado State University: Coordinated expression of myofibrillar protein isoforms in slow fibers of lobster (Homarus americanus) superficial abdominal muscles
Slow muscle fibers can be divided into two types in decapod crustaceans: slow phasic (S1) and slow tonic (S2). The purpose of this study was to examine the expression of myofibrillar protein isoforms in superficial abdominal muscles, which contain both S1 and S2 fibers. S1 fibers express primarily the following isoforms: troponin T3 (TnT3), S1 tropomyosin (S1Tm), S1 myosin heavy chain (S1MHC), and troponin I4 (TnI4). In contrast, S2 fibers express primarily TnT1, TnT3, S2Tm, S2MHC, and TnI2. At the protein level, expression of TnT, MHC, and TnI was measured by SDS-PAGE and Western blotting. At the mRNA level, expression of MHC and Tm was measured by RT-PCR. TnT3 protein and S1Tm mRNA positively correlated with S1MHC mRNA, while S2Tm was positively correlated with S2MHC. In addition, expression of certain TnI isoforms was correlated with certain TnT isoforms. For example, there was a strong inverse relationship between TnI2 and TnT3 proteins. In fact, expression of TnT and TnI demonstrated a continuum of isoform expression. Fibers expressing only TnT1 expressed mainly TnI2, while fibers expressing only TnT3 expressed mainly TnI4. Fibers expressing both TnT1 and TnT3 also expressed both TnI2 and TnI4. These data suggest that there is a coordinated expression of myofibrillar proteins isoforms. Moreover, analysis of single fibers showed a continuum of isoform expression patterns ranging from the S1 type to the S2 type. Factor(s) regulating gene expression are not known. However, it is hypothesized that innervation plays a role in the plasticity of myofibillar protein isoform expression. Support by NSF (IBN-0077422) and NIH (AR08597-01A1)
