spermatozoa lacking are incapable of fusing with the oocyte plasma membrane.

class genes encode sperm proteins with indispensable roles during fertilization. We have previously reported that belongs to the class, based on the finding that self-sperm of hermaphrodites were not consumed by fertilization. In this study, we directly observed live fertilization in the spermatheca of females after mating with males. As expected, it was clearly shown that mutant spermatozoa failed to fuse with the oocyte plasma membrane. Thus, our live imaging system for fertilization seems to be useful for evaluation of the functions of male and female gametes.