Worm Breeder's Gazette 17(2): 39 (April 1, 2002)

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.

EGL-32 may be a Sperm Protein that Regulates Egg Laying though the TGF-b Pathway

Marie McGovern, Ling Yu, Cathy Savage-Dunn

Dept of Biology, Queens College, CUNY, Flushing, NY 11367

A TGF-b related signaling pathway regulates dauer larval development and egg laying in C. elegans. Mutations in daf-7 ligand, daf-1 type I receptor, daf-4 type II receptor, and daf-8 and daf-14 Smads result in Dauer-constitutive/Egg-laying defective animals (1). These mutations are suppressed for both defects by mutations in daf-3 and daf-5 (2). We are interested in the role of this pathway in egg laying. Two other genes that affect egg laying, egl-4 and egl-32, are also implicated in this pathway by their suppression by daf-3 and daf-5 (3). Mutations in egl-4 also have a weak Dauer-constitutive phenotype (4). Mutants of egl-32 are the only known mutants to be suppressed by daf-3 and daf-5 that are Egg-laying defective, but not Dauer-constitutive.

Mutants of egl-32 retain about twice as many eggs as wild type animals: 30 instead of 14. Experimental evidence suggests that EGL-32 is a sperm protein that regulates egg laying in C. elegans. It has 3 close homologs, all of which are found in C. elegans. EGL-32 and its 3 closest homologs have been shown to be highly expressed in sperm (5). egl-32(n155) is a temperature sensitive mutation. Temperature shift assays reveal that L4 is the critical stage for EGL-32 inactivation. The L4 stage does not correspond to the time when eggs are laid, but when hermaphrodites produce sperm. Furthermore, the introduction of wild type sperm, by mating, into egl-32 animals results in a reduction in the number of eggs retained, and an increase in the number of eggs laid. The introduction of egl-32 sperm into wild type animals, by mating, causes wild type animals to lay fewer eggs and retain more eggs, many of which are at the comma stage or later.

It has previously been described that meiotic maturation and ovulation in C. elegans is regulated partially by sperm (6). In female mutants, oocytes fail to undergo meiotic maturation and sheath cell contraction, which is necessary for ovulation, is irregular (7). Introduction of sperm, by mating, causes oocytes to complete maturation and sheath cells to begin to contract regularly, allowing ovulation. It has recently been found that the major sperm protein (MSP) supplies the signal for oocyte maturation and ovulation (6) in C. elegans. It is possible that a mechanism also exists to coordinate the time of fertilization with the time of egg laying to insure that eggs are not laid too soon or too late. It is possible that this mechanism functions either directly or indirectly through the TGF-b pathway. Further experiments will be done to test this hypothesis.

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