A novel domain Caenorhabditis elegans wee-1.3, a member of the Myt1 kinase family, controls M-phase entry in sperm.

摘要

Control of the cell division cycle during the development of multicellular animals is not well understood. Several proteins that control of mitotic entry are conserved among all eukaryotes, but other proteins are unique to higher eukaryotes. All Wee1p-type kinases negatively regulate Cdc2p, the master positive regulator of mitotic entry in all eukaryotes, and are thus negative cell cycle regulatory molecules. WEE-1.3 is the C. elegans homolog of Myt1, which is a metazoan-specific isoform of the Wee1p kinase family. This dissertation describes the isolation and characterization of mutants in C. elegans wee-1.3, the first Myt1 mutants identified in any organism. Initial analyses involved the study of a set of independently derived dominant spermatogenesis-defective (Spe) mutants, which were shown to affect a single gene, spe-37. Genetic suppression of the dominant Spe phenotype led to the isolation of a complete allelic series for this gene, including semi-dominant, hypomorphic, and null mutants. These mutants revealed that WEE-1.3 is required for C. elegans development, since null mutants are embryonic and larval lethal. A candidate gene approach revealed that spe-37 was encoded by wee-1.3, a C. elegans homolog of the metazoan-specific Myt1 kinase. All dominant mutations are missense within a non-conserved region of WEE-1.3, and all missense suppressor mutations affect the Wee1p kinase domain. A WEE-1.3 polyclonal antibody was generated and used for immunolocalization studies, which show that WEE-1.3 localization is cell cycle-dependent in sperm, mitotic germ cells, and early blastomeres. In wee-1.3(gf) mutant spermatocytes, WEE-1.3 localization is indistinguishable from wild type spermatocytes at a similar stage of development. Since wee-1.3( gf) mutants have no consequences in oocytes or somatic cells, we hypothesize that WEE-1.3 is negatively regulated by an unknown sperm-specific regulatory pathway at the onset of spermatogenesis, and this signaling pathway is disrupted by wee-1.3(gf) mutants. Therefore, the continued study of C. elegans WEE-1.3 should lead to the identification of novel signaling pathways that function to developmentally regulate the cell cycle in metazoa.