Rewiring the Sex-Determination Pathway During the Evolution of Self-Fertility

Area of Science:

• Developmental biology
• Evolutionary genetics
• Molecular biology

Background:

• Evolutionary transitions in development are driven by changes in regulatory pathways.
• The molecular mechanisms underlying these developmental shifts remain largely unknown.
• The TRA-2 domain, crucial for TRA-1 interaction, is conserved across Caenorhabditis species.

Purpose of the Study:

• To investigate the molecular basis of evolutionary changes in sex determination pathways.
• To compare the function of the TRA-2/TRA-1 interaction in Caenorhabditis elegans and Caenorhabditis briggsae.
• To elucidate how alterations in protein interactions drive evolutionary transitions in development.

Main Methods:

• Comparative analysis of TRA-2 and TRA-1 protein interactions across two Caenorhabditis species.
• Introduction of identical mutations in the TRA-2 domain in both species.
• Examination of the effects of these mutations on oogenesis and spermatogenesis.
• Investigation of the role of the fem-3 gene in C. elegans sex determination.

Main Results:

• Identical mutations in the TRA-2 domain differentially regulate sexual development: promoting oogenesis in C. elegans and spermatogenesis in C. briggsae.
• The effects of these mutations are dependent on the fem-3 gene in C. elegans but independent in C. briggsae.
• Reciprocal mutations reveal that C. briggsae TRA-2 inhibits spermatogenesis regulators, while C. elegans TRA-1 sequesters TRA-2, enabling spermatogenesis initiation.

Conclusions:

• The direction of information flow within the sex determination pathway has likely switched during evolution between C. elegans and C. briggsae.
• This study provides a molecular example of how changes in conserved protein interactions can lead to significant evolutionary shifts in developmental processes.
• Understanding these molecular switches is key to comprehending the broader mechanisms of evolutionary change.