Sperm activation in <i>C. elegans</i>.

<p>(A) Sperm activation involves the initial formation of microspikes, the fusion of membraneous organelles (MOs) with the plasma membrane, and the extension of motile pseudopods. (B) In males, SWM-1 prevents precocious activation of stored sperm by inhibiting the male-specific, extracellular factor TRY-5. Active TRY-5 triggers sperm activation through an unknown signal transduction pathway. In hermaphrodites, sperm are activated via an unknown activator that acts through the <i>spe-8</i> signal transduction pathway. Both male and hermaphrodite sperm possess the two distinct signal transduction pathways (bottom row). The seminal fluid component TRY-5 can transactivate hermaphrodite sperm that have defects in the <i>spe-8</i> group genes. In one model, the activator of the <i>spe-8</i> signal transduction pathway is hermaphrodite-specific and activates <i>try-5</i> male sperm within the uterus. In an alternative model, the activator of the <i>spe-8</i> pathway is expressed in both hermaphrodites and, redundantly, in males. (C) Diagram of the <i>C. elegans</i> male gonad with the relative amount of TRY-5 within cells of the seminal vesicle, valve, and vas deferens indicated by different levels of gray shading.