A non-flight muscle isoform of Drosophila tropomyosin rescues an indirect flight muscle tropomyosin mutant.

The tropomyosin I(TmI) gene of Drosophila melanogaster encodes two isoforms of tropomyosin. The Ifm-TmI isoform is expressed only in indirect flight and jump muscles; the Scm-TmI isoform is found in other muscles of the larva and adult. The level of Ifm-TmI is severely reduced in the flightless mutant Ifm(3)3, which also is unable to jump. To explore the functional significance of tropomyosin isoform diversity in Drosophila, we have used P element-mediated transformation to express Scm-TmI in the indirect flight and jump muscles of Ifm(3)3 flies. Transformants gained the ability to jump and fly. The mechanical properties of isolated indirect flight muscle myofibres, and the ultrastructure of indirect flight and jump muscles from the transformants were comparable to wildtype. Thus, the Scm-TmI isoform can successfully substitute for Ifm-TmI in the indirect flight and jump muscles of the Ifm(3)3 strain.