Figure 1.

Fruitless, a gene in the sex-determination hierarchy, encodes multiple male-specific isoforms with distinct zinc finger domains. (A) The Drosophila somatic sex determination hierarchy has two branches--one regulates dosage compensation and the other somatic sexual development. In females (chromosomally XX) Sxl is produced and so dosage compensation is not active. In males there is no Sxl and dosage compensation is active, resulting in increased expression of the single male X chromosome. For somatic sexual development, Sxl regulates the splicing of its own pre-mRNA and the transformer (tra). The product of tra (Tra) along with Transformer-2 (Tra2), coordinate to regulate splicing of transcripts produced from doublesex (dsx) and the P1 promoter of fruitless (fru P1). This branch of the hierarchy culminates in the production of sex-specific transcription factors (Dsx^F, Dsx^M, and Fru^M) that specify sex-specific morphology and behaviors. Grey indicates transcripts; black indicates proteins. (B) Schematic of Fru^M proteins. Male-specific 101 amino acid region (Black), a bric-a-brac, tramtrack, broad-complex domain (BTB), and distinct zinc finger domains (A, B, or C) are indicated. (C)fruitless and doublesex locus. Coding exons (red bars), non-coding exons (black bars), sex-specifically spliced exon of fru (asterisks), first fru promoter (P1), exons encoding the zinc-finger DNA binding domains (A-D), and male- and female-specific exons for dsx are indicated. The DNA binding motifs (triangles) for A (purple), B (pink) or C (cyan) DNA binding domains of Fru^M are indicated.