Faithful transmission of chromosomes to daughter cells is fundamental to survival as loss or gain of even a single chromosome may contribute to birth defects or cancer. The spindle assembly checkpoint acts as a surveillance system to ensure that chromosomes are properly attached to the microtubule spindle before anaphase onset. In C. elegans , the homologs of yeast MAD2 and MAD1 checkpoint components have been identified in our lab and named
mdf-2 and
mdf-1 (Kitagawa and Rose, 1999 Nature Cell Biology 8:514). The C. elegans mutant strain KR3627 carries a
gk2 deletion within the
mdf-1 gene that results in maternal-effect lethality. The first generation of
mdf-1(
gk2) homozygotes, segregated from heterozygous parents, display no obvious phenotype. However, the second generation of
mdf-1(
gk2) worms produce very few progeny. The maternal effect lethality of the
mdf-1(
gk2) deletion strain was used as a genetic tool to search for functionally interacting gene products by means of identifying suppressors of the Mdf-1 lethal phenotype. Ten suppressors recovered from the screen increase the percentage of progeny that reach the adult stage and the percentage of fertile progeny, and can be maintained in a
gk2 homozygous background indefinitely. One suppressor strain recovered from this screen has been shown to encode the C. elegans homolog of Cdc20, FZY-1 (Kitagawa et al., 2002 Current Biology 12: 2118). Seven additional suppressors map to a chromosome II or III and two of the suppressors map to a chromosome V. An alternative way to discover additional checkpoint components that functionally interact with MDF-1 is to identify enhancers of Mdf-1 lethal phenotype. We have identified a strain carrying the
h2150 allele that on its own has no obvious phenotype, but in a
gk2 background causes significantly increased sterility in the first generation. The
h2150 allele has provided us with a clear enhancer phenotype, which will be used in genome-wide RNAi screens for enhancers of the Mdf-1 lethal phenotype. Funded by CIHR, Canada.