TISSUE-SPECIFICITY OF ARTHROPOD TROPOMYOSIN

In order to elucidate whether tropomyosin isoforms have different tissue-specific functions, we examined tissue specificity of tropomyosin by two-dimensional gel electrophoresis and immunoreplica tests using three arthropod species. These arthropods showed molecular heterogeneity and tissue specificity of tropomyosin in muscle and nonmuscle tissues. The beetle (Insecta) and centipede (Chilopoda) had three different isoforms. The scorpion (Arachnida) had six isoforms, two of which were nonmuscle-specific. In addition to these isoforms, all the species contained nonmuscle-specific isoforms of high electrophoretic mobilities and another isoform with a high electrophoretic mobility was found in the beetle heart and intestine. We summarized the results including the data from our previous studies on the horseshoe crab (Merostomata) and five crustaceans (Crustacea) and found that most isoforms were not shared by every tissue but detected in some particular tissues. In that sense, they were tissue specific, but each of them was not restricted to a single tissue. However, crustacean cardiac isoforms were contained exclusively in the hearts, and some of the nonmuscle isoforms were not found in other tissues; thus they were tissue specific in the strict sense. Considering our results and those on vertebrate tropomyosin together, we suggest that the existence of different isoforms alone does not imply straightforwardly different functions among the isoforms and that only strictly tissue-specific isoforms can be assumed to have functions peculiar to their tissues. (C) 1993 Wiley-Liss, Inc.