Gamete interactions require transmembranous immunoglobulin-like proteins with conserved roles during evolution

Area of Science:

• Reproductive Biology
• Developmental Biology
• Genetics

Background:

• Male germline-enriched genes in C. elegans, like spe-9, are vital for sperm-oocyte fusion.
• Identifying mammalian orthologs with similar functions has been difficult.
• Mouse Izumo1 encodes a sperm-specific Ig-like TM protein essential for gamete fusion.

Purpose of the Study:

• To identify and characterize C. elegans orthologs of male germline-enriched genes involved in gamete fusion.
• To investigate the function of the C. elegans spe-45 gene and its role in fertilization.
• To compare the function of C. elegans SPE-45 with mammalian IZUMO1.

Main Methods:

• Identification of C. elegans spe-45 gene with male germline-enriched expression and Ig-like TM protein structure.
• Analysis of spe-45 mutant worms for defects in sperm-oocyte fusion and sperm guidance.
• Phenotypic comparison with Izumo1-knockout mice.

Main Results:

• C. elegans spe-45 mutant worms exhibit defective sperm-oocyte fusion, similar to Izumo1-knockout mice.
• spe-45 may also play a role in sperm guidance from the uterus to the spermatheca.
• SPE-45 and IZUMO1 share conserved functions in gamete fusion, likely involving cis- and/or trans-partner binding.

Conclusions:

• The C. elegans spe-45 gene is essential for sperm-oocyte fusion and potentially sperm guidance.
• SPE-45 is functionally conserved with mouse IZUMO1, suggesting a conserved mechanism for gamete fusion.
• Ig-like TM proteins represent a widespread class of molecules utilized in gamete interactions and fertilization across diverse organisms.