Fig 1.
Schematic representations of stages of sperm motility activation.
(A) In humans, sperm are formed during spermatogenesis in the seminiferous tubules but are not motile nor competent to fertilize. During transit and storage in the epididymis, they undergo maturation to gain the ability to move. Upon delivery into the female reproductive tract, sperm become capable of fertilization through a process called capacitation, which alters the sperm head membrane to allow for membrane fusion and causes the sperm to become hypermotile. (B) In C. elegans, sperm are formed during spermatogenesis in both hermaphrodites and males. When males mate to hermaphrodites or when hermaphrodites switch to oocyte formation, sperm become activated. This activation causes the formation of the pseudopod that allows the sperm to crawl.
Fig 2.
Model for how zinc functions as a second messenger during C. elegans sperm activation.
Upon activation by the SPE-8 signaling pathway, zinc is released into the cytoplasm from intracellular storage organelles via ZIPT-7.1. High levels of cytoplasmic zinc activate yet-to-be-identified zinc-binding proteins that trigger the physiological changes to develop motility structures. SPE-8, spermatogenesis defective; ZIPT-7.1, Zrt- and Irt-like Protein Transporter 7.1.