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. 1.Savage-Dunn C, Cytokine and Growth Factor Reviews , 12, 2001 2.Patterson G.I.., Koweek A., Wong A., Liu Y. and Ruvkun G, Genes Dev. 11, 1997. 3.Trent C., Tsung N. and Horvitz H.R, Genetics. 104, 1983. 4.Daniels S.A., Ailion M., Thomas J.H. and Sengupta P, Genetics 156, 2000. 5.Reinke V., Smith H.E., Nance J., Wang J., Van Doren C., Begley R., Jones S.J.M., Davis E.B., Scherer S., Ward S., Kim S.K, Molecular Cell 6, 2000. 6.Miller M.A., Nguyen V.Q., Lee M., Kosinski M., Schedl T., Capriolo R.M. and Greenstein D. A, Science 291, 2001. 7.Strome S, J Cell Biol. 103, 1986.