Meeting Abstract

P2.136  Jan. 5  Alternative Splicing of the Myosin Heavy Chain in Loligo: A Squid Pro Quo Protein Distribution KIER, W.M.*; SCHACHAT, F.S.; Univ. of N. Carolina, Chapel Hill; Duke University billkier@bio.unc.edu

Specialization of muscle is a widespread and important factor in the evolution of motor systems. The means by which muscle fiber performance is modulated have been investigated in vertebrates and arthropods, but less is known about the mechanisms of muscle specialization in invertebrates in general. We explored the potential role of alternative splicing of the squid myosin heavy chain in modulation of muscle performance. The focus of the analysis was the transverse muscle of the tentacles and arms of the squid Loligo pealei. The transverse muscle of the tentacles is responsible for the unusually rapid strike used in prey capture and is serially homologous with the transverse muscle of the arms, which supports the slower arm movements. Previous studies showed that the tentacle muscle exhibits ultrastructural specializations for high shortening velocity. Comparison of protein profiles of myofilament preparations from the tentacle and arm fibers, however, revealed remarkably few differences in myofilamant lattice proteins. Since these techniques could not exclude the presence of a highly conserved variant that differs only in a few amino acids we performed semi-quantitative RT-PCR analysis of myosin heavy chain mRNAs from the tentacle and arm muscle. We found that a previously reported alternatively spliced isoform of the squid myosin motor domain is present only in low abundance in both muscle types and therefore differential expression of the two myosins cannot explain the difference in contractile properties. It appears that modulation of the performance of the muscle in cephalopods occurs primarily through variation in the arrangement and dimensions of the myofilaments, rather than through biochemical specialization.