Accurate chromosome segregation at the metaphase to anaphase transition is ensured by a highly regulated process. This transition is triggered by activation of the anaphase promoting complex (APC), which functions to target key proteins such as cyclin B or anaphase inhibitors, for ubiquitin mediated proteolysis (reviewed in Page and Hieter 1999). The APC is activated by WD-repeat proteins, which have been identified in all eukaryotes studied and fall into two distinct groups: fizzy and fizzy-related. In Saccharomyces cerevisiae , a fizzy protein, Cdc20, is known to activate APC to target an anaphase inhibitor, PdsI, and its degradation is essential to trigger sister chromatid separation. In addition, the spindle assembly checkpoint arrests cell cycle at metaphase before anaphase in response to spindle damage or kinetochore defects by inhibiting the APC activity via Cdc20. Thus, Cdc20 is a key component to regulate the timing of metaphase-anaphase transition during mitotic cell division in eukaryotes. We have been studying the mechanism of regulation of chromosome segregation in mitotically dividing cells during animal development using C. elegans . Recently we have identified a C. elegans homolog of budding yeast CDC20. The gene ZK177.6, tentatively named
fzy-1 , is located at about -1.8 map position on chromosome II. By yeast two-hybrid system, FZY-1 has been shown to interact with a spindle assembly checkpoint component, MDF-2. Loss of function by RNAi for
fzy-1 showed one-cell embryonic arrest phenotype, which is similar to " mat " (metaphase anaphase transition defective) phenotypes observed in
emb-27 (Golden et al 2000) or
emb-30 (Furuta et al 2000) mutants at restrictive temperature, suggesting that
fzy-1 is involved in APC activation. To address the question of how chromosome segregation is regulated by
fzy-1 gene product during animal development, we set out to isolate
fzy-1 deletion mutant strains by screening UV-TMP mutagenized worms. In the primary screen, we screened 9942 chromosomes by using the RNAi phenotype as a guideline, and obtained 201 candidates. One of these candidates,
h2066 , which displays the embryonic arrest phenotype, has been shown to have a deletion at the
fzy-1 locus by genomic PCR test. Using this strain, we are analyzing the FZY-1 function during development. The roles of FZY-1 in regulation of APC activation and MDF dependent checkpoint will be discussed. Furuta, T., S. Tuck, J. Kirchner, B. Koch, R. Auty, R. Kitagawa, A.M. Rose, and D. Greenstein. 2000. EMB-30: an APC4 homologue requied for mtaphase-to-anaphase transitions during meiosis and mitosis in Caenorhabditis elegans. Mol Biol Cell 11 : 1401-1419. Golden, A., P.L. Sadler, M.R. Wallenfang, J.M. Schumacher, D.R. Hamil, G. Bates, B. Bowerman, G. Seydoux, and D.C. Shakes. 2000. Metaphase to anaphase (mat) transition-defective mutants in Caenorhabditis elegans. J Cell Biol 151 : 1469-1482. Page, A.M. and P. Hieter. 1999. The anaphase-promoting complex: new subunits and regulators. Annu Rev Biochem 68 : 583-609.