Copulation in C. elegans males requires a nuclear hormone receptor

Area of Science:

• Developmental Biology
• Neuroscience
• Genetics

Background:

• The uncoordinated (unc)-55 gene encodes a nuclear hormone receptor essential for coordinated movement and male mating in *Caenorhabditis elegans*.
• UNC-55 plays a role in the nervous system and muscle function, with sexually dimorphic expression patterns observed.

Purpose of the Study:

• To investigate the role of UNC-55 in male mating behavior and identify its specific functions and regulatory mechanisms.
• To characterize the sexually dimorphic expression and alternative splicing of the *unc-55* gene in *C. elegans*.

Main Methods:

• Utilized a reporter gene to visualize *unc-55* expression patterns in different sexes and developmental stages.
• Employed RNA interference (RNAi) and behavioral analysis to assess the function of UNC-55 in male mating.
• Analyzed *unc-55* mRNA isoforms (a and b) in mutant and transgenic *C. elegans* to determine their specific roles.

Main Results:

• Reporter gene analysis revealed sexually dimorphic *unc-55* expression, including in male-specific neurons and muscles.
• Behavioral analysis demonstrated that males require UNC-55 for executing copulatory motor programs.
• Two *unc-55* mRNA isoforms (a and b) were identified; isoform b exhibited male-specific splicing and prolonged mating duration, suggesting an anabolic function.

Conclusions:

• *unc-55* gene expression and splicing are sexually dimorphic and regulated by male-specific genes (mab-5, mab-9).
• UNC-55 acts as a molecular interface, linking genes involved in male tail development to functional execution of mating behaviors.
• The male-specific isoform *unc-55b* is critical for mating behavior and may have an anabolic role in male reproductive function.