Yamanaka, MIkiko, Nishimura, Hitoshi, Shiraki, Riona, Shimada, Yoshihiro, Hashimoto, Masaharu, Kaneko, Mayumi, Ohkura, Kouhei, Omote, Masaaki, Hashiba, Youki, Karuo, Yukiko
[
International Worm Meeting,
2021]
In Caenorhabditis elegans, spermiogenesis undergoes two pivotal events; sperm formation and activation. Pseudopods extend from round spermatids to form motile spermatozoa, whereas membranous organelles (MOs) in spermatids fuse with the plasma membrane (PM) to activate spermatozoa. During the latter process, MOs release their contents extracellularly, and some proteins that are essential for fertilization relocate from the MO membrane onto the sperm surface, resulting in the acquisition of sperm fertility. These cytological features of MO fusion are similar to those of the acrosome reaction in mouse spermatozoa, representing one event for sperm activation. Thus, we hypothesized that C. elegans and the mouse might share a common mechanism for sperm activation. To explore this, we first screened a chemical library to obtain compounds that trigger C. elegans spermiogenesis. Of 480 entries contained in the library, we got several compounds as C. elegans spermiogenesis activators and chose one of the positive agents, named DDI-4, for further analyses. Intriguingly, 100 microM DDI-4 could induce the acrosome reaction in ~85% of mouse cauda epididymal spermatozoa, while ~70% became acrosome-reacted with 10 microM the calcium ionophore A23187. Moreover, DDI-4 promoted tyrosine phosphorylation of mouse sperm proteins, a typical capacitation signature, at least in vitro. These results indicate that DDI-4 can activate both C. elegans and mouse spermatozoa in vitro. In other words, these two species presumably possess targets of DDI-4 that function in sperm activation. To obtain clues regarding the DDI-4 targets or DDI-4-related factors, we screened mutants whose spermatids were resistant to DDI-4 in ethyl methanesulfonate-treated worms. Since two mutant strains were eventually isolated, we are currently investigating those strains by next-generation sequencing to identify mutated genes by which spermatids will become incapable of being activated with DDI-4. Information of such genes might contribute to elucidating the common mechanism for sperm activation in C. elegans and the mouse.