Tissue specificity of crustacean tropomyosin

The tropomyosin isoform distribution in muscle and nonmuscle tissues of crustaceans was investigated by two‐dimensional gel electrophoresis and immunoreplica tests. All five crustacean species examined in this study showed extensive molecular heterogeneity and tissue specificity of tropomyosin. The results were different from those previously reported with the horseshoe crab, that is, horseshoe crab tropomyosin was heterogeneous but not tissue‐specific. In this respect, therefore, the distribution of crustacean tropomyosin isoforms is more similar to that of vertebrate tropomyosin isoforms rather than that of horseshoe crab tropomyosin isoforms. Furthermore, crustacean nonmuscle tissues contained tropomyosin isoforms of high electrophoretic mobilities, which were possible counterparts of so‐called vertebrate nonmuscle isoforms of low molecular weights. However, it is rather difficult to expect that each tropomyosin isoform has a tissue‐specific function, since the patterns of isoform composition were not consistent among the examined crustaceans except for those of cardiac isoforms, which were unique to the hearts in all the examined crustaceans and correlated with the expression of presumed actin of compound peptides, which specifically appeared in the hearts. Therefore, the cardiac isoforms of crustacean tropomyosin are suggested to play tissue‐specific regulatory roles.