Worm Breeder's Gazette 14(2): 52 (February 1, 1996)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Germ Cells May Modulate the Smooth Muscle Activity of the Somatic Gonad for Ovulation in C. elegans

Jim McCarter, Bart Bartlett, Thanh Dang, Tim Schedl

Dept. of Genetics, Washington University School of Medicine, St. Louis, MO 63110, mccarter@genetics.wustl.edu

Successful ovulation of the mature oocyte from the gonad arm into the spermatheca (where fertilization occurs) requires contraction of the myoepithelial sheath and dilation of the myoepithelial distal spermatheca. How is the activity of these two non-innervated smooth muscle-like tissues regulated during ovulation? Examination of muscle movement upon alteration of the germ cell contents of the gonad reveals that somatic activity is dependent on the germ cells present.

Hermaphrodite Ovulation Motor Program. We have described the events of oocyte development, maturation, and ovulation [McCarter et al. (1995), WBG 14(1):68; also see Ward and Carrel (1979), Dev. Biol. 73:304; Doniach (1988), WBG 10(2):64]. The sheath contraction rate begins to increase ~30 minutes before the exit of the oocyte (Fig. 1A), and continues to increase during the visible events of oocyte maturation. The rate peaks as dilation of the distal spermatheca begins; the sheath then appears to tonically contract as it pulls the dilating distal spermatheca over the proximal oocyte (dilation lasts ~1 minute). The sheath contraction rate drops dramatically, and then begins to increase again for the next ovulation. An oocyte maturation/ovulation occurs in each arm every 51+/-14 minutes, n=33.

The Effect of Feminization on Oocyte Maturation and Sheath Activity. In unmated females which lack all sperm, including fog-1, -2, -3, and fem-1, -2, -3, oocytes arrest in diakinesis of meiotic prophase I for hours or days before maturation. (Maturation/ovulation occurs sporadically approximately once every 8.5 hours.) Introduction of sperm by mating restores the wild type occurrence of maturation/ovulation. Sperm therefore appear to act to promote maturation of the most proximal oocyte (Fig. 2A). Spermatids in the gonad arm or spermatozoa in the spermatheca both have the same effect, which is independent of their function at fertilization. (Many fer and spe mutants, which are incapable of fertilizing the oocyte, can still promote oocyte maturation.) In virgin adult females, we also observe that the rate of sheath contractions is significantly less than that observed at any time in adult hermaphrodites (Fig. 1B). Introduction of sp! erm by mating restores a hermaphrodite-like profile of sheath activity (Fig. 1C).

The Effect of Germline Masculinization on Sheath Activity. Is the sheath contractile rate low in females due to the absence of sperm, the absence of maturing oocytes, or the presence of many immature oocytes arrested in diakinesis? In the mutant fem-3(q20gf), which contains only sperm and no oocytes in the germ line but has a wild type soma (Mog phenotype), the sheath contracts at a high rate (Fig. 1D), similar to that observed in hermaphrodites and significantly higher than that observed in females. Therefore, spermatids may act independently of oocytes to promote sheath activity (Fig. 2B). Supporting this conclusion, we observe that in glp-1(oz112) animals (raised at 25 degrees), which contain germline tumors and lack sperm and oocytes, the sheath contractile rate is generally low (preliminary results, data not shown). While sperm probably promote sheath activity, the maturing oocyte also appears to play a role in the ovulation motor program. In! the absence of maturing oocytes (i.e. unmated females, Mog mutants, tumorous mutants), no sharp peak of sheath activity is observed as occurs during maturation and ovulation in hermaphrodites and mated females. Further, no dilation of the spermatheca is seen. The maturing oocytes may therefore act either directly or indirectly to modulate sheath activity (Fig. 2C) and spermatheca dilation (Fig. 2D) at ovulation.

Conclusions. The ovulation motor program completed by the sheath and spermatheca appears to be regulated by the sperm and oocytes for successful exit of the mature oocyte from the gonad arm. Further examination of somatic gonad response in mutants with germ line defects should better define the hypothesized interactions.