Sex determination: insights from the silkworm

Area of Science:

• Genetics
• Developmental Biology
• Insect Biology

Background:

• Sex determination mechanisms exhibit significant diversity across insect species.
• The genetic hierarchy controlling somatic sexual differentiation in Drosophila melanogaster (X:A > Sxl > tra/tra2 > dsx and fru) is well-characterized.
• This cascade is partially conserved in other dipterans, but distinct systems exist, such as in Bombyx mori.

Purpose of the Study:

• To investigate the role and regulatory mechanism of the doublesex (dsx) homolog in the silkworm, Bombyx mori (Bmdsx).
• To compare the sex-specific alternative splicing of Bmdsx with that of dsx in Drosophila.
• To identify novel regulatory factors involved in Bmdsx splicing.

Main Methods:

• Comparative genomics to identify Bmdsx.
• Analysis of Bmdsx mRNA isoforms and their alternative splicing patterns.
• Identification and characterization of regulatory proteins involved in Bmdsx splicing, including BmPSI.

Main Results:

• Bombyx mori utilizes a W chromosome-based feminizing factor for sex determination, lacking Sxl and tra homologs.
• Bmdsx produces sex-specific mRNA isoforms, analogous to dsx, encoding transcription factors.
• Female splicing of Bmdsx is the default pathway, while male splicing is regulated by the splicing inhibitor BmPSI.
• BmPSI lacks sequence homology to known SR proteins like Tra and Tra2.

Conclusions:

• The regulatory mechanism for sex-specific alternative splicing of Bmdsx in Bombyx mori is distinct from the dsx regulatory pathway in Drosophila.
• The findings highlight novel strategies for sex determination and gene regulation in insects.
• BmPSI represents a unique class of splicing regulators in insect sex determination.