AUTOREGULATION OF THE SPLICING OF TRANSCRIPTS FROM THE TRANSFORMER-2 GENE OF DROSOPHILA

The Drosophila transformer-2 gene uses alternative promoters and splicing patterns to generate four different mRNAs that together encode three putative RNA-binding polypeptides. The transformer-2 products expressed in somatic tissues function to regulate the RNA splicing of the sex determination gene doublesex, whereas products expressed in the male germ line play an unknown, but essential, role in spermatogenesis. Two alternatively spliced transformer-2 transcripts, each encoding a different putative RNA-binding protein, are found only in the male germ line. These male germ line-specific mRNAs differ from each other by the presence or absence of a single intron called M1. We show that M1-containing transcripts make up a majority of transformer-2 germ-line transcripts in wild-type males but fail to accumulate in males homozygous for transformer-2 null mutations. Germ-line transformation experiments using a variety of reporter gene constructs demonstrate that specific polypeptide products of the transformer-2 gene itself normally repress M1 splicing in the male germ line. Thus, in addition to its role in the sex-specific control of doublesex RNA splicing in somatic tissues, the transformer-2 gene also regulates the splicing of its own transcripts in the male germ line. We propose that this autoregulatory function may serve in negative feedback control of transformer-2 activity during spermatogenesis. The finding that transformer-2 controls multiple splicing decisions suggests that a variety of different alternative splicing choices could be regulated by a relatively limited number of trans-acting factors.