A negative feedback mechanism revealed by functional analysis of the alternative isoforms of the Drosophila splicing regulator transformer-2

The Drosophila sex determination gene transformer-2 (tra-2) is a splicing regulator that affects the sex specific processing of several distinct pre- mRNAs. While the tra-2 gene itself is known to produce alternative mRNAs that together encode three different TRA-2 protein isoforms, the respective roles of these isoforms in affecting individual pre-mRNA targets has remained unclear. We have generated transgenic fly strains with mutations affecting specific TRA-2 isoforms to investigates their individual roles in regulating the alternative processing of doublesex, exuperantia and tra-2 pre-mRNA. Our results indicate that in somatic tissues two different isoforms function redundantly to direct female differentiation and female specific doublesex pre-mRNA splicing. In the male germline, where tra-2 has an essential role in spermatogenesis, a single isoform was found to uniquely perform all necessary functions. This isoform appears to regulate its own synthesis during spermatogenesis through a negative feedback mechanism involving intron retention.