What is the role of the Sxl (sex lethal) protein in female Drosophila?

The Sxl (sex lethal) protein plays a crucial role in the determination of sexual identity in Drosophila by regulating gene expression related to sex differentiation. In females, Sxl is responsible for the proper splicing of its own mRNA and that of the Tra (transformer) gene, which is essential for female development. Specifically, Sxl binds to its own pre-mRNA, preventing its splicing into a non-functional form, thereby allowing for the production of the fully functional Sxl protein.

By suppressing the splicing of both Sxl and Tra, Sxl ensures that the female development pathway remains active. This regulation allows the female-specific isoforms of other proteins to be produced, leading to female characteristics. Essentially, Sxl acts as a master switch in the sex determination pathway of Drosophila, promoting the female developmental trajectory.

The other options do not accurately represent the function of Sxl. For example, the role of Sxl is not to activate male gene expression, facilitate mRNA translation, or act primarily as a transcription enhancer, but rather to maintain and control the expression of specific female genes through alternative splicing mechanisms.