The C. elegans hermaphrodite proximal gonad is encircled by 6 myoepithelial sheath cells (1). Contractions of the sheath are responsible for expelling the oocyte from the gonad arm at ovulation. Ablating sheath cells (2) or disrupting their ability to contract (3) can abolish ovulation. Our evidence suggests that both sperm and oocytes modulate the contractile activity of the sheath during the ovulation motor program. The events of oocyte development, maturation, and ovulation (4) were analyzed using time-lapse Nomarski microscopy with anesthetized (5) wild type hermaphrodites and various mutants altering the composition of the germ line. In each arm, ovulations occur at approximately 50 minute intervals. In the minutes after the most proximal oocyte in the gonad arm matures, contractile activity in the myoepithelial sheath peaks in both frequency and intensity. The peak coincides with dilation of the distal spermatheca, allowing the most proximal oocyte to exit the gonad arm at ovulation. After ovulation, sheath contractile activity diminishes before recovering for the next ovulation. Changing the composition of the C. elegans germ line changes the frequency and pattern of the myoepithelial sheath contractions. Mutations which feminize the germ line [
fog-1(
q180),
fog-2(
q71),
fog-3(
q443),
fem-3(
e1996)] greatly reduce the frequency of sheath contractions. Mating into these females restores contractions with the same cyclic pattern observed in ovulating hermaphrodites. Since the introduction of sperm promotes oocytes to mature (6) as well as the sheath to contract, it was unclear from this experiment whether sperm were directly causing the sheath to contract or causing contractions indirectly through the maturing oocytes. We therefore examined mutations which masculinize the germ line [
mog-2(
q75),
fem-3(
q20gf),
gld-1(
oz10)]. In these mutants which produce sperm but no oocytes, the sheath contracts at a steady high frequency. This suggests that sperm in the gonad arm can directly stimulate sheath activity in the absence of oocytes. We are further testing the effect of sperm by quantitating sheath activity in tumorous germlines which have no differentiated germ cells [
gld-1(
q485),
glp-1(
oz112)] with and without the introduction of sperm into the spermatheca by mating. In summary, these experiments suggest that 1) sperm promote sheath contractile activity, and 2) maturing oocytes provides a cyclic pattern to this activity. This germline regulation of somatic myoepithelial activity may be required to couple maturation to the ovulation motor program. Since the gonadal sheath lacks innervation, germ cell to sheath communication appears to be direct rather than through the nervous system. 1 Strome, S (1986). JCB, 103:2241-2252. 2 McCarter, J., et al. (1996). In preparation. 3 Myers, C., et al. (1996). JCB, In press. 4 McCarter, J., et al. (1995). WBG, 14,1:68-69. 5 Kirby, C., et al. (1990). Dev. Bio., 142:203-215. 6 McCarter, J., et al. (1996). WBG, 14,2:52-53.