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 splic ing regulator that affects the sex-specific processing of several dist inct pre-mRNAs. While the tra-2 gene itself is known to produce altern ative mRNAs that together encode three different TRA-2 protein isoform s, the respective roles of these isoforms in affecting individual pre- mRNA targets has remained unclear. We have generated transgenic fly st rains with mutations affecting specific TRA-2 isoforms to investigate their individual roles in regulating the alternative processing of dou blesex, exuperantia and tra-2 pre-mRNA. Our results indicate that in s omatic tissues two different isoforms function redundantly to direct f emale differentiation and female-specific doublesex pre-mRNA splicing. In the male germline, where tra-2 has an essential role in spermatoge nesis, a single isoform was found to uniquely perform all necessary fu nctions. This isoform appears to regulate its own synthesis during spe rmatogenesis through a negative feedback mechanism involving intron re tention.