title: Maternal MEMI Promotes Female Meiosis II in Response to Fertilization in Caenorhabditis elegans.
abstract: In most animals, female meiosis completes only after fertilization. Sperm entry has been implicated in providing a signal for the initiation of the final meiotic processes; however, a maternal component required for this process has not been previously identified. We report the characterization of a novel family of three highly similar paralogs (memi-1, memi-2, memi-3) that encode oocyte-specific proteins. A hyper-morphic mutation memi-1(sb41) results in failure to exit female meiosis II properly; however, loss of all three paralogs results in a "skipped meiosis II" phenotype. Mutations that prevent fertilization, such as fer-1(hc1), also cause a skipped meiosis II phenotype, suggesting that the MEMI proteins represent a maternal component of a postfertilization signal that specifies the meiosis II program. MEMI proteins are degraded before mitosis and sensitive to ZYG-11, a substrate-specific adapter for cullin-based ubiquitin ligase activity, and the memi-1(sb41) mutation results in inappropriate persistence of the MEMI-1 protein into mitosis. Using an RNAi screen for suppressors of memi-1(sb41), we identified a sperm-specific PP1 phosphatase, GSP-3/4, as a putative sperm component of the MEMI pathway. We also found that MEMI and GSP-3/4 proteins can physically interact via co-immunoprecipitation. These results suggest that sperm-specific PP1 and maternal MEMI proteins act in the same pathway after fertilization to facilitate proper meiosis II and the transition into embryonic mitosis.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Maryam
authors.initials: M
authors.lastname: Ataeian
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Justus
authors.initials: J
authors.lastname: Tegha-Dunghu
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Donna G
authors.initials: DG
authors.lastname: Curtis
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Ellen M E
authors.initials: EM
authors.lastname: Sykes
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Ashkan
authors.initials: A
authors.lastname: Nozohourmehrabad
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Megha
authors.initials: M
authors.lastname: Bajaj
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Karen
authors.initials: K
authors.lastname: Cheung
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada srayko@ualberta.ca.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0003-0196-0364
authors.initials: M
authors.lastname: Srayko
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000502:physiology; D029742:Caenorhabditis elegans Proteins / Q000235:genetics* / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005306:Fertilization / Q000235:genetics*; D008297:Male; D008540:Meiosis / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009865:Oocytes / Q000166:cytology / Q000378:metabolism*; D011485:Protein Binding; D059748:Proteolysis
chemical_list: D029742:Caenorhabditis elegans Proteins; D018797:Cell Cycle Proteins; C106933:FER-1 protein, C elegans; C000619334:MEMI-1 protein, C elegans; D008565:Membrane Proteins; C454942:zyg-11 protein, C elegans
keywords: Caenorhabditis elegans; PP1 phosphatase; female meiosis; fertilization; mitosis