Multiple response elements in the Sex-lethal early promoter ensure its female-specific expression pattern

Area of Science:

• Developmental Biology
• Genetics
• Molecular Biology

Background:

• Sexual identity in Drosophila melanogaster is established early in embryogenesis.
• The X-chromosome-to-autosome (X/A) ratio is the primary signal determining sexual fate.
• The Sex-lethal (Sxl) gene acts as a binary switch, initiating female development.

Purpose of the Study:

• To investigate how the X/A signaling system controls initial sexual identity choice.
• To elucidate the role of the early embryonic Sxl promoter (Sxl-Pe) in sex determination.
• To understand the regulatory mechanisms of numerator and denominator genes on Sxl-Pe activity.

Main Methods:

• Analysis of the Sxl promoter (Sxl-Pe) in early embryos.
• Functional dissection of Sxl-Pe regulatory elements.
• Examination of gene dosage effects of X-linked numerator and autosomal denominator genes.

Main Results:

• Sxl-Pe activity is highly dose-sensitive to X-linked numerator and autosomal denominator genes.
• Female development requires the cumulative action of multiple numerator genes on Sxl-Pe.
• Male development relies on repressive activities of denominator genes on Sxl-Pe, involving specific target sequences.

Conclusions:

• The X/A ratio precisely controls early sexual identity through dose-dependent regulation of the Sxl promoter.
• Numerator genes activate Sxl-Pe in females via reiterated cis-acting sites.
• Denominator genes repress Sxl-Pe in males through target sequences within the promoter.