In both yeast and mammals, uncapped telomeres activate the DNA damage response (DDR) and undergo end-to-end fusion1,2. Previous work has shown that the Drosophila HOAP protein, encoded by the caravaggio (cav) gene, is required to prevent telomeric fusions3. Here we show that HOAP-depleted telomeres activate both the DDR and the spindle assembly checkpoint (SAC). The cell cycle arrest elicited by the DDR was alleviated by mutations in mei-41 (encoding ATR), mus304 (ATRIP), grp (Chk1) and rad50 but not by mutations in tefu (ATM). The SAC was partially overridden by mutations in zw10 (also known as mit(1)15) and bubR1, and also by mutations in mei-41, mus304, rad50, grp and tefu. As expected from SAC activation, the SAC proteins Zw10, Zwilch, BubR1 and Cenp-meta (Cenp-E) accumulated at the kinetochores of cav mutant cells. Notably, BubR1 also accumulated at cav mutant telomeres in a mei-41-, mus304-, rad50-, grp- and tefu-dependent manner. Our results collectively suggest that recruitment of BubR1 by dysfunctional telomeres inhibits Cdc20-APC function, preventing the metaphase-to-anaphase transition.
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We thank M.L. Goldberg, B. Williams, C. Sunkel, C. Lehner, T. Megraw, J. Raff, T. Kaufman and T.T. Su for providing antibodies and Drosophila strains, and M.L. Goldberg for critical comments on the manuscript. This work was supported by grants from the Italian Association for Cancer Research (AIRC) and Telethon to M.G. and by a grant for Progetti di Ricerca di Interesse Nazionale (PRIN) from Ministero dell'Università e Ricerca (MIUR) to G.C.
Supplementary Methods, Supplementary Figures 1–3 (PDF 3906 kb)
Visualization of the mitotic division of a wild type neuroblast expressing His2AvDGFP. (AVI 430 kb)
Visualization of the delayed mitotic division of a cav mutant neuroblast expressing His2AvDGFP. (AVI 879 kb)
Visualization of the delayed mitotic division of a cav/ Df(3R)crb-F89-4 mutant neuroblast expressing His2AvDGFP. (AVI 571 kb)
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Musarò, M., Ciapponi, L., Fasulo, B. et al. Unprotected Drosophila melanogaster telomeres activate the spindle assembly checkpoint. Nat Genet 40, 362–366 (2008). https://doi.org/10.1038/ng.2007.64