Model for ZIPT-7.1 function.

<p>(A) Model of the genetic function of <i>zipt-7</i>.<i>1</i>. The black line shows the plasma membrane, and arrows and bars indicate positive and negative interactions, respectively. Genes that mutate to sperm activation defective or constitutive are green or red, respectively. (B) Model of the biochemical function of ZIPT-7.1 at three times during sperm activation: (1) Primed spermatid: prior to activation, spermatids are primed to respond—ZIPT-7.1 (dark blue) is inactive and localized to the membrane of a vesicle that has a high internal concentration of stored zinc (orange circles) and is presumably the membranous organelle (light blue). The cytoplasm has a low concentration of zinc, and the equilibrium of zinc-regulated proteins (purple) is shifted towards unbound. (2) Release: a sperm-activating signal results in activation of ZIPT-7.1 (orange arrow), zinc begins to flow into the cytoplasm, and zinc-regulated proteins begin binding zinc. (3) Activated spermatozoon: the cytoplasmic concentration of zinc is now high, and zinc-regulated proteins are bound to zinc. The pseudopod extension begins (lower), and the membranous organelles fuse with the plasma membrane. Fusion of membranous organelles is based on previously published observations of this event [<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2005069#pbio.2005069.ref028" target="_blank">28</a>], and our results do not directly address whether ZIPT-7.1 is relocalized during this process.