Cholesterol and the biosynthesis of glycosphingolipids are required for sperm activation in Caenorhabditis elegans.

Ejaculated mammalian sperm must acquire fertilization capacity after residing into the female reproductive tract, a process collectively known as capacitation. Cholesterol efflux was required for sperm maturation. Different from flagellated sperm, C. elegans sperm are crawling cells. C. elegans sperm are highly enriched with cholesterol though this animal species lacks biosynthetic pathway for cholesterol and its survival requires an exogenous cholesterol supply. The low abundance of cholesterol in C. elegans lipid extract is thought insufficient to form lipid microdomains ubiquitously in this organism. We present evidence that cholesterol is enriched in the plasma membrane of C. elegans spermatids and that cholesterol- and glycosphingolipids (GSLs)-enriched membrane microdomains (lipid microdomains) mediate sperm activation. Disruption of sperm lipid microdomains by acute manipulation of cholesterol in vitro blocks the sperm activation. Restriction of cholesterol uptake also results in the abnormal sperm activation in both males and hermaphrodites. Manipulation of the integrity of lipid microdomains by targeting the biosynthesis of GSLs inhibits sperm activation and the inhibition can be rescued by the addition of exogenous GSLs. The cleavage of glycosylphosphatidylinositol (GPI)-anchored proteins, which are exclusively found in lipid microdomains, also affects sperm activation. We conclude that localized signaling mediated by lipid microdomains is critical for worm sperm activation. Lipid microdomains composed of cholesterol and GSLs have been observed in flagellated sperm of several animal species, thus cholesterol, before its efflux from the plasma membrane, might be needed to assemble into a platform for some more important upstream signal sorting during spermatogenesis than was previously thought.

Nematode sperm maturation triggered by protease involves sperm-secreted serine protease inhibitor (Serpin).

Spermiogenesis is a series of poorly understood morphological, physiological and biochemical processes that occur during the transition of immotile spermatids into motile, fertilization-competent spermatozoa. Here, we identified a Serpin (serine protease inhibitor) family protein (As_SRP-1) that is secreted from spermatids during nematode Ascaris suum spermiogenesis (also called sperm activation) and we showed that As_SRP-1 has two major functions. First, As_SRP-1 functions in cis to support major sperm protein (MSP)-based cytoskeletal assembly in the spermatid that releases it, thereby facilitating sperm motility acquisition. Second, As_SRP-1 released from an activated sperm inhibits, in trans, the activation of surrounding spermatids by inhibiting vas deferens-derived As_TRY-5, a trypsin-like serine protease necessary for sperm activation. Because vesicular exocytosis is necessary to create fertilization-competent sperm in many animal species, components released during this process might be more important modulators of the physiology and behavior of surrounding sperm than was previously appreciated.