The vertebrate- and testis- specific transmembrane protein C11ORF94 plays a critical role in sperm-oocyte membrane binding

Abstract

Sperm-oocyte membrane fusion is necessary for mammalian fertilization. The factors that determine the fusion of sperm with oocytes are largely unknown. So far, spermatozoon factor IZUMO1 and the IZUMO1 counter-receptor JUNO on the oocyte membrane has been identified as a protein requiring fusion. Some sperm membrane proteins such as FIMP, SPACA6 and TEME95, have been proved not to directly regulate fusion, but their knockout will affect the fusion process of sperm and oocytes. Here, we identified a novel gene C11orf94 encoding a testicular-specific small transmembrane protein that emerges in vertebrates likely acquired via horizontal gene transfer from bacteria and plays an indispensable role in sperm-oocyte binding. We demonstrated that the deletion of C11orf94 dramatically decreased male fertility in mice. Sperm from C11orf94-deficient mice could pass through the zona pellucida, but failed to bind to the oocyte membrane, thus accumulating in the perivitelline space. In consistence, when the sperm of C11orf94-deficient mice were microinjected into the oocyte cytoplasm, fertilized oocytes were obtained and developed normally to blastocysts. Proteomics analysis revealed that C11orf94 influenced the expression of multiple gene products known to be indispensable for sperm-oocyte binding and fusion, including IZUMO1, EQTN and CRISP1. Thus, our study indicated that C11ORF94 is a vertebrate- and testis-specific small transmembrane protein that plays a critical role in sperm binding to the oolemma.

1700029I15Rik orchestrates the biosynthesis of acrosomal membrane proteins required for sperm–egg interaction

“…Recently, two independent studies on 1700029I15Rik were published ( 42 , 43 ). Despite that the knockout mouse lines exhibit the same phenotype, the works by three groups show great discrepancies in terms of the proposed molecular functions of 1700029I15Rik.…”

“…S2 J ), Hao et al. ( 43 ) reported that 1700029I15Rik knockout male mice show significantly reduced sperm counts. The authors performed proteomic analyses on wild-type and knockout whole testis and sperm and identified a multitude of downregulated proteins in the knockout groups ( 43 ).…”

“…( 43 ) reported that 1700029I15Rik knockout male mice show significantly reduced sperm counts. The authors performed proteomic analyses on wild-type and knockout whole testis and sperm and identified a multitude of downregulated proteins in the knockout groups ( 43 ). We are concerned that the decreased sperm counts in that mouse line may reflect changes in the germ cell populations (i.e., reduced percentages of round spermatids or testicular sperm in knockout testes), which potentially complicates the interpretation of the MS outcomes.…”

“…4 H ), the proteomic analysis by Hao et al. revealed that IZUMO1 and EQTN are downregulated in the knockout sperm ( 43 ).…”

The role of SPP/SPPL intramembrane proteases in membrane protein homeostasis

“…Frey1 is a small type II‐oriented protein that resides within the ER. In mice, it is exclusively expressed in round spermatids from stages V to VIII but absent from mature spermatozoa [72]. As demonstrated by two independent groups, Frey1 physically interacts with SPPL2c both in cell‐based overexpression systems but also in vivo in the murine testis, while not being proteolytically processed [71,73].…”