Caenorhabditis elegans BUB-3 and SAN-1/MAD3 Spindle Assembly Checkpoint Components Are Required for Genome Stability in Response to Treatment with Ionizing Radiation

Relatively little is known about the crosstalk between the spindle assembly checkpoint and the DNA damage response, especially in multicellular organisms. We performed a Caenorhabditis elegans forward genetic screen to uncover new genes involved in the repair of DNA damage induced by ionizing radiation. We isolated a mutation, gt2000 which confers hypersensitivity to ionizing radiation and showed that gt2000 introduces a premature stop in bub-3. BUB-3 is a key component of the spindle assembly checkpoint. We provide evidence that BUB-3 acts during development and in the germline; irradiated bub-3(gt2000) larvae are developmentally retarded and form abnormal vulvae. Moreover, bub-3(gt2000) embryos sired from irradiated worms show increased levels of lethality. Both bub-3 and san-1 (the Caenorhabditis elegans homologue of MAD3) deletion alleles confer hypersensitivity to ionizing radiation, consistent with the notion that the spindle assembly checkpoint pathway is required for DNA damage response. bub-3(gt2000) is moderately sensitive to the crosslinking drug cisplatin but not to UV light or methyl methanesulfonate. This is consistent with role in dealing with DNA double-strand breaks and not with base damage. Double mutant analysis revealed that bub-3 does not act within any of the three major pathways involved in the repair of double-strand breaks. Finally, the cdc-20 gain-of-function mutant cdc-20/fzy-1(av15), which is refractory to the cell cycle delay conferred by the spindle checkpoint showed phenotypes similar to bub-3 and san-1 mutants. We speculate that BUB-3 is involved in DNA damage response through regulation of cell cycle timing.

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