The metaphase to anaphase (met-ana) transition in mitotic cells is controlled by the activity of the Anaphase Promoting Complex (APC). APC is an E3 ubiquitin ligase that targets proteins for destruction in order for sister chromatids to separate at anaphase. The substrates of APC include cyclins, anaphase inhibitors, and chromosome cohesins. The APC is composed of at least 12 subunits in S. cerevisiae; mutations in these genes result in metaphase arrest. Temperature sensitive mutations in 6 genes disrupt the met-ana transition during meiosis I in C. elegans embryos. These genes are
mat-1, -2, -3 (for met-ana transition defective),
emb-1, -27, & -30 (Miwa et al., 1980; Cassada et al., 1981; Furuta et al., 2000; Nishiwaki & Miwa, WBG 10; Golden et al., 1999 Int. WM). Homozygous mothers shifted to 25C produce broods of 1-cell arrested embryos in which the oocyte chromosomes congress and set up a meiotic spindle after fertilization. However, the first meiotic division fails to occur, anaphase is never observed, polar bodies are never extruded, and pronuclei never form. The sperm chromosomes remain condensed and the sperm centrosomes fail to nucleate microtubule asters. The
emb-30 gene was recently shown to encode an
apc4 homolog (Furuta et al., 2000) and
emb-27 a
cdc16 homolog (another APC subunit; Sadler & Shakes, pers. comm.). Genetic mapping of
mat-1 places it on LG I near another APC subunit gene,
cdc27. RNAi of this gene results in the production of 1-cell arrested embryos that fail to progress through meiosis I. We have sequenced this
cdc27 gene from a number of
mat-1 alleles and found mutations in the
cdc27 coding region for each. Based on 2-cell embryo and L1 shift-up experiments, the 6
mat-1 alleles make up an alleleic series. Two alleles are >95% lethal even at 15C and are maintained as balanced heterozygotes. Another 2 alleles result in sterility when embryos or L1s are shifted to 25C. The last 2 alleles are maternal-effect embryonic lethal; these animals, when shifted to 25C as 2-cell embryos, develop normally and produce 1-cell arrested embryos. We will show the sequence alterations and the phenotypic characterization of these 6
mat-1 alleles.