Expression and function of the Drosophila ACT88F actin isoform is not restricted to the indirect flight muscles.

Most higher eukaryotic genomes contain multiple actin genes, yet the sequence differences between isoforms are few. In Drosophila melanogaster it was previously established that one of the six actin genes, Act88F, is expressed only in the indirect flight muscles (IFMs). These muscles are highly specialised for oscillatory contractions to power flight. The implication was that this isoform had tissue-specific properties. In this paper we show using two reporter constructs expressing either beta-galactosidase, Act88F-lacZ, or the green fluorescent protein, Act88F-GFP, that the Act88F promoter is active in a small number of other muscles, including leg (femoral) and uterine muscles. However, the levels of Act88F driven non-IFM expression are much less than in the IFMs. We have confirmed endogenous Act88F gene expression in these other muscles by in situ hybridisation studies. Using null and antimorphic mutants to show decreased walking ability and delayed/reduced oviposition we demonstrated that Act88F expression is functionally important in multiple muscle groups. Since the mutant effects are mild, this supports the expectation that other actin genes are also expressed in these muscles. The Act88F-GFP promoter-reporter also detects Act88F-driven expression in the bristle-forming cells in the pupal wings. The implications of these results for the functions and developmental expression of the Drosophila ACT88F isoform are discussed.