Lineage-Specific Gene Expansion and Atypical Expression Pattern of Feminizing Gene Transformer in Stag Beetles

Area of Science:

• Evolutionary Biology
• Genetics
• Entomology

Background:

• Insect sex determination relies on conserved downstream genes like doublesex (dsx), often regulated by the Transformer (Tra) protein.
• The Tra gene is typically a single copy, but its number can vary, making it a focus for studying evolutionary changes in sex determination.
• The conventional understanding is that functional Tra is female-specific, inducing female development through dsx splicing.

Purpose of the Study:

• To investigate the copy number and expression patterns of the Transformer (Tra) gene in stag beetles (Lucanidae).
• To explore evolutionary variations in insect sex determination mechanisms, specifically within the Coleoptera order.

Main Methods:

• Comparative genomics to identify Tra gene copy number variations in stag beetle species.
• Analysis of Tra gene splicing variants in both male and female stag beetles.
• Phylogenetic analysis to understand the evolutionary history of Tra gene duplication.

Main Results:

• The Transformer (Tra) gene has undergone expansion via gene duplication in several stag beetle species.
• Contrary to the typical pattern, the Tra gene exhibits identical splicing variants in both male and female stag beetles in studied species.
• These findings indicate a deviation from the conserved insect sex determination pathway within the Lucanidae family.

Conclusions:

• The Lucanidae family presents a unique evolutionary trajectory for the Tra gene, differing in copy number and sex-specific expression.
• Tra gene expansion and altered expression patterns in stag beetles provide novel insights into the diverse evolutionary strategies of insect sex determination.
• This study challenges the generalized model of Tra-mediated sex determination and highlights the plasticity of this fundamental biological process.