Mutations in ooc-5 and ooc-3 disrupt oocyte formation and the reestablishment of asymmetric PAR protein localization in two-cell Caenorhabditis elegans embryos.
The early development of Caenorhabditis elegans embryos is characterized by a series of asymmetric divisions in which the mitotic spindle is repeatedly oriented on the same axis due to a rotation of the nuclear-centrosome complex. To identify genes involved in the control of spindle orientation, we have screened maternal-effect lethal mutants for alterations in cleavage pattern. Here we describe mutations in ooc-5 and ooc-3, which were isolated on the basis of a nuclear rotation defect in the P(1) cell of two-cell embryos. These mutations are novel in that they affect the asymmetric localization of PAR proteins at the two-cell stage, but not at the one-cell stage. In wild-type two-cell embryos, PAR-3 protein is present around the entire periphery of the AB cell and prevents nuclear rotation in this cell. In contrast, PAR-2 functions to allow nuclear rotation in the P(1) cell by restricting PAR-3 localization to the anterior periphery of P(1). In ooc-5 and ooc-3 mutant embryos, PAR-3 was mislocalized around the periphery of P(1), while PAR-2 was reduced or absent. The germ-line-specific P granules were also mislocalized at the two-cell stage. Mutations in ooc-5 and ooc-3 also result in reduced-size oocytes and embryos. However, par-3 ooc double-mutant embryos can exhibit nuclear rotation, indicating that small size per se does not prevent rotation and that PAR-3 mislocalization contributes to the failure of rotation in ooc mutants. We therefore postulate that wild-type ooc-5 and ooc-3 function in oogenesis and in the reestablishment of asymmetric domains of PAR proteins at the two-cell stage.
Basham
S E
SE
Section of Molecular and Cellular Biology, University of California at Davis, One Shields Avenue, Davis, California 95616, USA.
Rose
L S
LS
D000818:Animals; D017173:Caenorhabditis elegans / Q000196:embryology* / Q000235:genetics; D029742:Caenorhabditis elegans Proteins; D017238:Genes, Helminth / Q000502:physiology*; D015801:Helminth Proteins / Q000032:analysis*; D009154:Mutation; D009866:Oogenesis; D017346:Protein Serine-Threonine Kinases
D029742:Caenorhabditis elegans Proteins; D015801:Helminth Proteins; C087977:par-2 protein, C elegans; C097238:PAR-3 protein, C elegans; D017346:Protein Serine-Threonine Kinases