Fission yeast strains with circular chromosomes require the 9-1-1 checkpoint complex for the viability in response to the anti-cancer drug 5-fluorodeoxyuridine

Exploring Genetic Interactions with Telomere Protection Gene pot1 in Fission Yeast

The regulation of telomere length has a significant impact on cancer risk and aging in humans. Circular chromosomes are found in humans and are often unstable during mitosis, resulting in genome instability. Some types of cancer have a high frequency of a circular chromosome. Fission yeast is a good model for studying the formation and stability of circular chromosomes as deletion of pot1 (encoding a telomere protection protein) results in rapid telomere degradation and chromosome fusion. Pot1 binds to single-stranded telomere DNA and is conserved from fission yeast to humans. Loss of pot1 leads to viable strains in which all three fission yeast chromosomes become circular. In this review, I will introduce pot1 genetic interactions as these inform on processes such as the degradation of uncapped telomeres, chromosome fusion, and maintenance of circular chromosomes. Therefore, exploring genes that genetically interact with pot1 contributes to finding new genes and/or new functions of genes related to the maintenance of telomeres and/or circular chromosomes.

The fission yeast bromodomain protein Bdf2 is required for the growth of cells with circular chromosomes

Circular chromosomes have frequently been observed in tumors of mesenchymal origin. In the fission yeast Schizosaccharomyces pombe, deletion of pot1+ results in rapid telomere loss, and the resulting survivors have circular chromosomes. Fission yeast has 2 bromodomain and extra-terminal (BET) proteins, Bdf1 and Bdf2; both are required for maintaining acetylated histones. Here, we found that bdf2, but not bdf1, was synthetically lethal with pot1. We also obtained a temperature-sensitive bdf2-ts mutant, which can grow at high temperatures but becomes camptothecin sensitive. This suggests that Bdf2 is defective at high temperatures. The cell cycle of the pot1 bdf2-ts mutant was delayed in the G2 and/or M phase at a semipermissive temperature. Furthermore, a temperature-sensitive mutant of mst1, which encodes histone acetyltransferase, showed a synthetic growth defect with a pot1 disruptant at a semipermissive temperature. Our results suggest that Bdf2 and Mst1 are required for the growth of cells with circular chromosomes.