Model for adult somatic sex maintenance in the <i>Drosophila</i> somatic gonad.

<p>Left: In XX animals, the production of Sxl leads to alternative splicing of <i>tra</i> pre-mRNA into <i>tra</i>^<i>F</i>. Tra^F protein then alternatively splices <i>dsx</i> pre-mRNA into <i>dsx</i>^<i>F</i>. The Dsx^F protein promotes female-specific transcriptional changes. Right: In XY animals, Sxl is not produced. Neither <i>tra</i> nor <i>dsx</i> pre-mRNA are alternatively spliced, resulting in the production of Dsx^M protein, which ensures male-specific transcription of target genes. In addition to the absence of Sxl in XY cells, adult somatic stem cells of the <i>Drosophila</i> testis have an extra level of insurance of male sex identity. Chinmo, which is expressed only in male but not female somatic gonadal cells, represses expression of <i>tra</i>, <i>vir</i> and <i>fl(2)d</i> in CySCs. This safeguards male identity by reducing the availability of <i>tra</i> pre-mRNA and of factors (i.e., Vir and Fl(2)d)) that can splice it into <i>tra</i>^<i>F</i>. Thus, in addition to the canonical sex determination pathway that establishes male and female programs from early development, adult male, sexually dimorphic cells protect their sexual identity by transcriptional repression of <i>tra</i> and its splice factors.