The Anaphase Promoting Complex or Cyclosome (APC/C) is a multisubunit ubiquitin ligase, which causes the destruction of cell-cycle regulators leading to the segregation of chromosomes at anaphase and exit from mitosis and meiosis. Previously, we described 32 temperature-sensitive C. elegans mutants that defined five genes, three of which were novel. At the non-permissive temperature of 25 degrees, all 32 mutant adults produce embryos arrested at the 1-cell embryonic stage, with their sperm and oocyte chromatin highly condensed, while polar bodies are absent. The phenotypes of these mutants indicates that they are arrested at the metaphase-to-anaphase transition of meiosis I in oocytes. We termed the three novel genes "mat" (metaphase-to-anaphase transition-defective). In addition, each mat gene is represented by some alleles that exhibit germline mitotic and somatic defects. Genetic mapping demonstrated that all three mat genes mapped near C. elegans orthologs of APC subunits. To reveal the molecular identity of these genes, we determined the DNA sequences of the appropriate APC subunit genes in several alleles of each complementation group. The results indicate that in all cases, a given mat mutation occurred in the predicted APC subunit gene. Further, RNA interference using the predicted APC subunit genes gave the same 1-cell meiotic arrest phenotype as the mutants at the non-permissive temperature. We conclude that
mat-1 ,
mat-2 , and
mat-3 are all alleles of C. elegans APC subunit genes. We also analyzed sperm development and function in Mat mutant males. For these experiments, we focused on
mat-3 , because this complementation group represents the largest allelic series of the three. Although all thirteen
mat-3 alleles exhibited similar oocyte meiosis defects, they differed in their sperm meiosis and mitotic germline defects. In L3 upshift experiments, four categories of sperm meiosis defects were observed: fully fertile males (3 alleles); weakly fertile males (1 allele); infertile males with aneuploid sperm (3 alleles); infertile males with largely anucleate sperm (6 alleles). The five alleles that exhibited germline mitosis defects in L1 upshift experiments produced infertile males in L3 upshift experiments, but the alleles did not split evenly between the aneuploid and anucleate categories. Finally, we identified
som-1 , an extragenic suppressor of the
mat-3 oocyte meiosis phenotype. Suppression in
mat-3 ;
som-1 animals was only partially penetrant within a given brood, giving rise to only 3%-15% viable embryos at the non-permissive temperature. This suggests that, along with other phenotypes, aberrant chromosome segregation is occurring in order to allow
mat-3 animals to reproduce. Characterization of the
som-1 gene will be discussed. We postulate that
som-1 encodes a protein that physically interacts with the protein encoded by
mat-3 .