For sexual reproduction in most animal species, spermiogenesis is an essential, post-meiotic event in which spermatids transform into spermatozoa. During C. elegans spermiogenesis, pseudopods extend from spermatids, and membranous organelles (MOs) are fused with the spermatid plasma membrane. C. elegans is so useful for studying spermiogenesis; in addition to easy availability of various genetic tools, we can use in vitro spermiogenesis system in a simple, chemically defined medium. This advantage allows us to use compounds that can directly control spermatid activation into spermatozoa to dissect the C. elegans spermiogenesis pathway.
Based on microscopic observation of Pronase-induced in vitro spermiogenesis, we screened a library of compounds with diverse structures. One compound, named DDI-1, blocked pseudopod extension, but not MO fusion with the spermatid plasma membrane (IC50 = ~30 μM). Since DDI-1 did not affect the proteolytic activity of Pronase towards FITC-casein, the compound seemed to target a spermatid protein(s) that is involved in pseudopod extension.
Moreover, we examined brood sizes after incubation of L4 hermaphrodites with DDI-1 at 20ºC for 48 h in liquid culture. The compound-treated worms, unexpectedly, produced F1 progeny ~50% more than control worms. As spermatids were released from DDI-1-treated males and then activated with Pronase, spermiogenesis normally occurred. These data suggest that, in liquid culture, DDI-1 probably does not reach spermatids present within the male gonads and that this compound has an additional effect(s) on reproduction besides blocking spermiogenesis.
Currently we are producing a series of DDI-1 derivatives to identify its target(s) and keeping to screen the same library to obtain more compounds that affect spermiogenesis.