| Abstract: | We have partially characterized four Drosophilamelanogaster alpha-actinin gene mutants,I(1)2Cb1, I(1)2Cb2,I(1)2Cb4, and I(1)2Cb5. Wedemonstrate that in each case the mutation is caused bya chromosomal rearrangement that precludes normal proteinsynthesis. In the absence of alpha-actinin, fliescomplete embryogenesis and develop into flaccid larvaethat die within approximately 24 hr. These larvae have noticeable muscle dysfunction at hatching,although they, nevertheless, are capable of escapingfrom the egg membranes and of subsequent crawlingmovements. During larval development muscles degenerate, progressively limiting mobility and ultimatelycausing death. Electron microscopy of mutant musclefibers reveals that myofibrils are grossly disrupted inone day old larvae and that electron-dense structures reminiscent of those seen in human nemalinemyopathies are present throughout larval life. Our workrigorously demonstrates that alpha-actinin deficienciesare the cause of I(1)2Cb muscle defects. We anticipate that the alpha-actinin mutants described hereinwill facilitate in vivo tests of spectrin superfamilyprotein domain functions using a combination of directedmutagenesis and germline transformation. |
