Pot1 promotes telomere DNA replication via the Stn1-Ten1 complex in fission yeast

Abstract Telomeres are nucleoprotein complexes that protect the chromosome-ends from eliciting DNA repair while ensuring their complete duplication. Pot1 is a subunit of telomere capping complex that binds to the G-rich overhang and inhibits the activation of DNA damage checkpoints. In this study, we explore new functions of fission yeast Pot1 by using a pot1-1 temperature sensitive mutant. We show that pot1 inactivation impairs telomere DNA replication resulting in the accumulation of ssDNA leading to the complete loss of telomeric DNA. Recruitment of Stn1 to telomeres, an auxiliary factor of DNA lagging strand synthesis, is reduced in pot1-1 mutants and overexpression of Stn1 rescues loss of telomeres and cell viability at restrictive temperature. We propose that Pot1 plays a crucial function in telomere DNA replication by recruiting Stn1-Ten1 and Polα-primase complex to telomeres, thus promoting lagging-strand DNA synthesis at stalled replication forks

Pot1 promotes telomere DNA replication via the Stn1-Ten1 complex in fission yeast

International audienceTelomeres are nucleoprotein comple x es that protect the chromosome-ends from eliciting DNA repair while ensuring their complete duplication. Pot1 is a subunit of telomere capping complex that binds to the G-rich o v erhang and inhibits the activation of DNA damage c hec kpoints. In this study, w e e xplore ne w functions of fission y east Pot1 b y using a pot1-1 temperature sensitive mutant. We show that pot1 inactivation impairs telomere DNA replication resulting in the accumulation of ssDNA leading to the complete loss of telomeric DNA. Recruitment of Stn1 to telomeres, an auxiliary factor of DNA lagging strand synthesis, is reduced in pot1-1 mutants and o v ere xpression of Stn1 rescues loss of telomeres and cell viability at restrictive temperature. We propose that Pot1 pla y s a crucial function in telomere DNA replication by recruiting Stn1-Ten1 and Pol α-primase complex to telomeres via Tpz1, thus promoting lagging-strand DNA synthesis at stalled replication forks

The fission yeast Stn1-Ten1 complex limits telomerase activity via its SUMO-interacting motif and promotes telomeres replication

International audienceMammalian CST (CTC1-STN1-TEN1) complex fulfills numerous functions including rescue of the stalled replication forks and termination of telomerase action. In fission yeast lacking the CTC1 ortholog, the Stn1-Ten1 complex restricts telomerase action via its sumoylation-mediated interaction with Tpz(1TPPl). We identify a small ubiquitin-like modifier (SUMO)-interacting motif (SIM) in the carboxyl-terminal part of Stn1 and show that this domain is crucial for SUMO and Tpz1-SUMO interactions. Point mutations in the SIM (Stn1-226) lead to telomere elongation, impair Stn1-Ten1 recruitment to telomeres, and enhance telomerase binding, revealing that Stn1 SIM domain contributes to the inhibition of telomerase activity at chromosome ends. Our results suggest that Stn1-Ten1 promotes DNA synthesis at telomeres to limit single-strand DNA accumulation. We further demonstrate that Stn1 functions in the replication of telomeric and subtelomeric regions in a Taz1-independent manner. Genetic analysis reveals that misregulation of origin firing and/or telomerase inhibition circumvents the replication defects of the stnl-226 mutant. Together, our results show that the Stn1-Ten1 complex has a dual function at telomeres by limiting telomerase action and promoting chromosome end replication

FoxM1 repression during human aging leads to mitotic decline and aneuploidy-driven full senescence

This deposit is composed by a publication in which the IGC's authors have had the role of collaboration (it's a collaboration publication). This type of deposit in ARCA is in restrictedAccess (it can't be in open access to the public), and can only be accessed by two ways: either by requesting a legal copy from the author (the email contact present in this deposit) or by visiting the following link: https://www.nature.com/articles/s41467-018-05258-6This deposit is composed by the main article and the supplementary materials are present in the publisher's page in the following link: https://www.nature.com/articles/s41467-018-05258-6#Sec36Aneuploidy, an abnormal chromosome number, has been linked to aging and age-associated diseases, but the underlying molecular mechanisms remain unknown. Here we show, through direct live-cell imaging of young, middle-aged, and old-aged primary human dermal fibroblasts, that aneuploidy increases with aging due to general dysfunction of the mitotic machinery. Increased chromosome mis-segregation in elderly mitotic cells correlates with an early senescence-associated secretory phenotype (SASP) and repression of Forkhead box M1 (FoxM1), the transcription factor that drives G2/M gene expression. FoxM1 induction in elderly and Hutchison-Gilford progeria syndrome fibroblasts prevents aneuploidy and, importantly, ameliorates cellular aging phenotypes. Moreover, we show that senescent fibroblasts isolated from elderly donors' cultures are often aneuploid, and that aneuploidy is a key trigger into full senescence phenotypes. Based on this feedback loop between cellular aging and aneuploidy, we propose modulation of mitotic efficiency through FoxM1 as a potential strategy against aging and progeria syndromes.E.L. holds an FCT Investigator Postdoctoral Grant (IF/00916/2014) from FCT/MCTES (Fundação para a Ciência e a Tecnologia/Ministério da Ciência, Tecnologia e Ensino Superior). FCT Fellowships (SFRH/BD/74002/2010; SFRH/BD/125017/2016; PD/BD/128000/2016) supported J.C.M., S.V., and R.R. The following project grants supported this work: National Funds through FCT under the project PTDC/BEX-BCM/ 2090/2014 ; NORTE-01-0145-FEDER-000029 funded by North Regional Operational Program (NORTE2020) under PORTUGAL 2020 Partnership Agreement through Regional Development Fund (FEDER); NORTE-07-0124-FEDER-000003 co-funded by North Regional Operational Program (ON.2) through FEDER and by FCT; and POCI-01-0145-FEDER-007274 i3S framework project co-funded by COMPETE 2020/PORTUGAL 2020 through FEDER and by FCT; Foundation Pediatric Oncology Groningen grant and Dutch Cancer Society grant 2012-RUG-5549 to F.F.info:eu-repo/semantics/publishedVersio

Ssu72 phosphatase is a conserved telomere replication terminator

International audienceTelomeres, the protective ends of eukaryotic chromosomes, are replicated through concerted actions of conventional DNA poly-merases and elongated by telomerase, but the regulation of this process is not fully understood. Telomere replication requires (Ctc1/ Cdc13)-Stn1-Ten1, a telomeric ssDNA-binding complex homologous to RPA. Here, we show that the evolutionarily conserved phos-phatase Ssu72 is responsible for terminating the cycle of telomere replication in fission yeast. Ssu72 controls the recruitment of Stn1 to telomeres by regulating Stn1 phosphorylation at Ser74, a residue located within its conserved OB-fold domain. Consequently, ssu72Δ mutants are defective in telomere replication and exhibit long 3 0-ssDNA overhangs, indicative of defective lagging-strand DNA synthesis. We also show that hSSU72 regulates telomerase activation in human cells by controlling recruitment of hSTN1 to telomeres. These results reveal a previously unknown yet conserved role for the phosphatase SSU72, whereby this enzyme controls telomere homeostasis by activating lagging-strand DNA synthesis, thus terminating the cycle of telomere replication