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.

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The process of sperm-egg fusion is critical for successful fertilization, yet the underlying 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) sperm 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 sperm can bind to the oolemma, they show the fusion defect, resulting that Dcst1 KO males become almost sterile and Dcst2 KO males become sterile. Similar to mice, zebrafish dcst1 KO males are subfertile and dcst2 and dcst1/2 double KO males are sterile. Zebrafish dcst1/2 KO sperm are motile and can approach the egg, but are defective in binding to the oolemma. Furthermore, we find that DCST1 and DCST2 interact with each other and are interdependent. These data demonstrate that DCST1/2 are essential for male fertility in two vertebrate species, highlighting their crucial role as conserved factors in fertilization.

mechanism of clinical variability associated with SCN10A-related diseases remain unclear.In conclusion, we suggest, for the first time, the association of SCN10A variants with isolated congenital harlequin syndrome. These data need to be confirmed by additional cases and further studies on the alterations of channel gating.Acknowledgments: we wish to thank the patients and their families for their collaboration. This work complies with the Committee on Publication Ethics (COPE) guidelines on good publication. We also thank V. Raclin, E. Faubert-Lauge and G. Gricourt for valuable technical assistance.