Odorant receptor-mediated sperm activation in disease vector mosquitoes

Area of Science:

• Entomology
• Molecular Biology
• Reproductive Biology

Background:

• Insects rely on chemoreceptors for behaviors like host-seeking and oviposition.
• Odorant receptors (ORs) form ion channel complexes crucial for many insect chemosensory pathways.
• The function of ORs in non-olfactory tissues, such as testes, remains largely unexplored.

Purpose of the Study:

• To investigate the potential role of odorant receptors (ORs) in mediating sperm responses to endogenous signaling molecules in the malaria vector mosquito, Anopheles gambiae.
• To explore the presence and function of ORs in insect spermatozoa across different species.

Main Methods:

• Investigated AgOr transcript expression in Anopheles gambiae testes.
• Utilized immunofluorescence to determine the localization of the OR coreceptor (AgOrco) in Anopheles gambiae spermatozoa.
• Assessed the activation of sperm flagella beating in response to Orco-specific agonists, antagonists, and odorant ligands.
• Examined Orco expression and function in spermatozoa of Aedes aegypti and other insect taxa.

Main Results:

• AgOr transcripts were detected in Anopheles gambiae testes.
• AgOrco was localized to the flagella of Anopheles gambiae spermatozoa.
• Orco-dependent activation of sperm flagella beating was observed in response to various ligands.
• Orco expression and Orco-mediated sperm activation were confirmed in Aedes aegypti.
• Orco localization in testes was found across diverse insect groups.

Conclusions:

• Odorant receptors and their coreceptor Orco are present and functional in insect spermatozoa.
• OR-mediated responses in spermatozoa may play a significant role in insect reproduction.
• This phenomenon could represent a widespread characteristic of insect reproduction and an instance of convergent evolution.