Mutations affecting the indirect flight muscles of Drosophila melanogaster

The development of the indirect flight muscles of Drosophila melanogaster was studied by analysing mutations that cause flightlessness. Twenty-five mutations on the X-chromosome and two on the third chromosome were examined. The X-chromosomal mutations form ten complementation units. The ten loci were assigned preliminary map positions by meiotic recombination and deficiencies and duplications. The two autosomal mutationsrepresent two genes. Gynandromorph analyses suggest that many of these mutations have their primary effect inthe presumptive thoracic muscle region of the embryo. The mutations cause a variety of characteristic defects, such as absence of the bulk of the thoracic muscle mass, or absence of only one of the two fibrillar musclegroups. Electronmicroscopic studies of sixteen mutants representing all twelve loci reveal abnormal myofibrillar organization in some of these mutants, e.g. aberrant or missing Z-bands, or absence of the thin filaments. Mutant protein patterns, obtained by SDS-polyacrylamide gel electrophoresis, show the following differences from wild type: ten mutants are characterized by absence or reduction of the 54 K protein, and most mutants exhibit a reduction and modification of the 80 and 90 K proteins. The absence or reduction of the 54 K proteinwas strongly correlated with aberrant Z-bands.