Sperm membrane proteins DCST1 and DCST2 are required for the sperm-egg fusion process in mice and fish

Abstract

The process of sperm-egg fusion is critical for successful fertilization, yet the underpinning mechanisms that regulate these steps have remained unclear in vertebrates. Here, we show that both mouse and zebrafish DCST1 and DCST2 are necessary in sperm to fertilize the egg, similar to their orthologs SPE-42 and SPE-49 in C. elegans and Sneaky in D. melanogaster. Mouse Dcst1 and Dcst2 single knockout (KO) spermatozoa are able to undergo the acrosome reaction and show normal relocalization of IZUMO1, an essential factor for sperm-egg fusion, to the equatorial segment. While both single KO spermatozoa can bind to the oolemma, they rarely fuse with oocytes, resulting in male sterility. Similar to mice, zebrafish dcst1 KO males are subfertile and dcst2 and dcst1/2 double KO males are sterile. Zebrafish dcst1/2 KO spermatozoa are motile and can approach the egg, but rarely bind to the oolemma. These data demonstrate that DCST1/2 are essential for male fertility in two vertebrate species highlighting their crucial role as conserved factors in fertilization.

The conserved fertility factor SPACA4/Bouncer has divergent modes of action in vertebrate fertilization

“…3 ). SPACA4, therefore, differs from the proposed function of other known sperm fertility factors required for sperm–egg interaction in mice (SPACA6, IZUMO1, SOF1, FIMP, TMEM95, and DCST1/2), which are required at the later step of sperm–egg membrane binding and/or fusion ( 4 – 12 ). Thus, our work provides genetic evidence for an important function of SPACA4 for the step of ZP binding in mice.…”

“…Branches supported by ultrafast bootstrap values (≥95%) are marked with a blue dot. Z-scores of averaged gene expression values across adult tissues are shown on the right for Danio rerio ( 11 ), Xenopus laevis ( 75 ), Mus musculus ( 73 ), and Homo sapiens ( www.gtexportal.org ). While Bouncer/Spaca4 mRNAs are expressed in oocytes in fish and frogs, mammalian Spaca4 mRNAs are expressed in testis.…”

“…Xenopus laevis expression data were derived from the NCBI Gene Expression Omnibus (GEO) entry GSE73419 ( 75 ). Danio rerio expression data were derived from GEO entries GSE111882 (testis, ovary, and mature oocytes) ( 42 ), GSE147112 (oogenesis and mature oocytes) ( 76 ), and GSE171906 (adult tissues) ( 11 ). Heatmaps were used to illustrate the relative expression levels of genes across tissues.…”

“…Previously published data were used for this work that are available on the publicly accessible database GEO [ Danio rerio expression data were derived from GEO entries GSE111882 (testis, ovary, and mature oocytes) ( 42 ), GSE147112 (oogenesis and mature oocytes) ( 76 ), and GSE171906 (adult tissues) ( 11 )]. The Spaca4 knockout mice, C57BL/6N-Spaca4 tm1Osb , were deposited into the RIKEN BioResource Center ( https://mus.brc.riken.jp/en/ ) and are available to the scientific community.…”

“… 1 – 3 ). Required proteins on the sperm are the transmembrane proteins IZUMO1 ( 4 , 5 ), SPACA6 ( 6 , 7 ), TMEM95 ( 7 – 9 ), FIMP ( 10 ), DCST1/2 ( 11 , 12 ), and the secreted protein SOF1 ( 8 ). The factors required on the egg are the tetraspanin protein CD9 ( 13 – 15 ) as well as the glycosylphosphatidylinositol (GPI)-anchored protein JUNO ( 16 ).…”