emo-1, a Caenorhabditis elegans Sec61p gamma homologue, is required for oocyte development and ovulation.

Abstract

Abstract. emo-l(ozl) is a member of a class of hermaphrodite sterile mutations in Caenorhabditis elegans that produce endomitotic oocytes in the gonad arm. Oocytes in emo-1 (ozl) mutants exhibit multiple defects during oogenesis. After meiotic maturation, ovulation fails, trapping oocytes in the gonad arm where they become endomitotic, erno-1 encodes a homologue of the Sec61p ~/subunit, a protein necessary for translocation of secretory and transmembrane proteins into the endoplasmic reticulum of yeast and mammalian cells. A putative emo-1 null mutation, oz151, displays embryonic lethality. The ozl sterile mutation is a transposable element insertion into the emo-1 3' untranslated region that almost completely eliminates germline mRNA accumulation. Genetic mosaic analysis using the ozl allele indicates that emo-1 (+) expression in germ cells is required for fertility. The J67 monoclonal antibody, which recognizes an oocyte surface antigen (Strome, S. 1986. In Gametogenesis and the Early Embryo. J.G. Gall, editor. Alan R. Liss, Inc., New York. 77-95.), does not stain ozl oocytes, a finding consistent with defective protein transport in the mutant. We propose that the emo-1 gene product acts in the transport of secreted and transmembrane proteins in C. elegans oocytes, and is necessary for both oogenesis and the coupling of ovulation with meiotic maturation.OG~NESIS, meiotic maturation, and ovulation are critical processes that prepare the oocyte for fertilization and embryogenesis in sexually reproducing metazoans (Masui and Clark, 1979). Oogenesis requires the controlled production and storage of structural proteins, enzymes, maternal mRNAs, and determinants (Davidson, 1986;Lasko, 1992). In many species, maturation requires the regulated activation of the cdc2/Cyclin B complex (Mailer et al., 1989) to allow cell cycle progression from late prophase to metaphase of meiosis I. Ovulation, the release of the oocyte from the ovary, is coordinated with maturation in species as diverse as starfish (Kanatani et al., 1969), nematodes (Ward andCarrel, 1979), insects (Doane, 1960), and mammals (Channing et al., 1978). In mammals, all three processes are regulated by gonadotropin release from the pituitary, as well as by the actions of the surrounding somatic ovarian cells. Follicle cells, for instance, appear to prevent maturation by producing high levels of cAMP delivered to the oocyte via gap junctions (Buccione et al., 1990;Wickramasinghe and Albertini, 1993). Ovarian smooth muscle cells contract to expel the oocyte at ovulation (Diaz-Infante et al., 1975 The nematode Caenorhabditis elegans offers an attractive system for the study of oogenesis, maturation, and ovulation owing to its genetic accessibility and the ease with which oocytes can be monitored in real time within living animals. The C. elegans hermaphrodite gonad is composed of two arms, each filled with germ cells that proliferate in a distal zone and enter meiotic prophase and differentiate proximally (Hirsh et al., 1976;Kimble and Ward, 1988;Clifford et al...

Tropomyosin and Troponin Are Required for Ovarian Contraction in theCaenorhabditis elegansReproductive System

“…However, in both CeTMI,II (RNAi) and CeTMI, II,III,IV (RNAi) worms, oocytes at the proximal gonads had a large accumulation of DNA ( Figure 1d, arrowhead), indicating that there was endomitotic replication of DNA in the oocytes, which became highly polyploid. This phenotype resembles the previously described endomitotic oocytes in gonadal arms phenotype (Emo) that is observed when ovulation is defective (Iwasaki et al, 1996). The Emo phenotype of CeTM (RNAi) worms was very severe, such that oocytes or embryos were not observed in the spermatheca or uterus ( Figure 1b and Table 1), suggesting that there was no ovulation.…”

“…Thus, when the cleavage was complete, the nucleus was restricted to only one of the two daughter cells, leaving the other cell anuclear (Figure 2j, asterisk; Video 2). In the absence of ovulation, maturation of the second or third proximal oocyte was often observed (our unpublished data), indicating that a signal to induce oocyte maturation can reach distally located oocytes as demonstrated previously (Iwasaki et al, 1996). Therefore, suppression of TM specifically caused a defect in the contractile activity of the ovary, but not in the process of oocyte maturation.…”

Structural components of the nonstriated contractile apparatuses in the Caenorhabditis elegans gonadal myoepithelial sheath and their essential roles for ovulation

“…When ovulation fails, a mature oocyte remains in the proximal ovary, repeats DNA synthesis without cell division, and becomes endomitotic (Iwasaki et al, 1996;McCarter et al, 1997McCarter et al, , 1999. This phenotype is designated as Emo (endomytotic oocytes in the proximal ovary) and is characterized by intense staining by 4Ј6-diamidino-2-phenylindole, dihydrochloride (DAPI) of overly amplified nuclear DNA in endomitotic oocytes ( Fig.…”

“…This phenotype is designated as Emo (endomytotic oocytes in the proximal ovary) and is characterized by intense staining by 4Ј6-diamidino-2-phenylindole, dihydrochloride (DAPI) of overly amplified nuclear DNA in endomitotic oocytes ( Fig. 7C, arrows; Iwasaki et al, 1996). The ovulation process is also regulated by signals from sperm and oocytes.…”

Multiple Functions and Dynamic Activation of MPK-1 Extracellular Signal-Regulated Kinase Signaling inCaenorhabditis elegansGermline Development

“…org/supplemental/). Time-lapse analysis has shown that the Emo phenotype results when the oocyte undergoes maturation but ovulation fails, with the resulting unfertilized oocyte remaining in the gonad and undergoing endoreduplication cycles (Iwasaki et al 1996;McCarter et al 1997;Rose et al 1997). The Emo phenotype observed with partial mpk-1 lf suggests that maturation occurred normally but ovulation failed; however, until these intermittent/low-frequency events Germline MPK-1 Function and Activation 2051 are examined by time-lapse microscopy, this interpretation is uncertain.…”