Muscle type-specific myosin isoforms in crustacean muscles

Differential expression of multiple myosin heavy chain (MyHC) genes largely determines the diversity of critical physiological, histochemical, and enz ymatic properties characteristic of skeletal muscle. Hypotheses to explain myofiber diversity range from intrinsic control of expression based on myob last; lineage to extrinsic control by innervation, hormones, and usage; The unique innervation and specialized function of crayfish (Procambarus clark ii) appendicular and abdominal musculature provide a model to test these hy potheses. The leg opener and superficial abdominal extensor muscles are inn ervated by tonic excitatory motoneurons. High resolution SDS-PAGE revealed that these two muscles express the same MyHC profile. In contrast, the deep abdominal extensor muscles, innervated by phasic motoneurons, express MyHC profiles different from the tonic profiles. The claw closer muscles are du ally innervated by tonic and phasic motoneurons and a mixed phenotype was o bserved, albeit biased toward the phasic profile seen in the closer muscle. These results indicate that multiple MyHC isoforms are present in the cray fish and that differential-expression is associated with diversity of muscl e type and function. J. Exp. Zool. 286:36-48, 2000. (C) 2000 Wiley-Liss, In c.