Meta-analysis of MTHFR C677T polymorphism and type 2 diabetes mellitus in MENA region.

BACKGROUND AND AIMS: The association of the C677T polymorphism of the Methylenetetrahydrofolate Reductase (MTHFR) gene with susceptibility to type 2 diabetes mellitus (T2DM) has been widely debated. Therefore, our aim is to conclusively resolve this controversy in the Middle East and North Africa region population through a meta-analysis. MATERIEL AND METHODS: We identified relevant articles by searching literature databases, such as PubMed, Web of Science, and Science Direct, to retrieve studies that examined the association between the MTHFR C677T polymorphism and the risk of developing T2DM. Using meta-analysis, we calculated the odds ratio (OR) and confidence interval (CI) values of these studies to assess the susceptibility to T2DM related to the C677T polymorphism of MTHFR gene. RESULTS: In this meta-analysis, we included a total of 13 publications comprising 2072 T2DM patients and 2164 control subjects. The results of the meta-analysis suggested that there is a significant association between the C677T polymorphism and T2DM risk in overall comparisons for allele contrasts (T vs C): OR = 1.25, 95% CI = 1.04-1.50, p = 0.015 and homozygous (TT vs CC): OR = 1.44, 95% CI = 1.01-2.05, p = 0.038). Subgroup analysis revealed that the C677T polymorphism is associated with a risk of T2DM in Asian populations, while there is no significant association between this polymorphism and T2DM in Caucasian and African populations. Furthermore, there was no evidence of publication bias. CONCLUSION: Our study's results suggest that the allele contrast of the C677T polymorphism of the MTHFR gene is associated with an increased risk of T2DM in the overall population, particularly among Asians.

Cell cycle-dependent spatial segregation of telomerase from sites of DNA damage.

Telomerase can generate a novel telomere at DNA double-strand breaks (DSBs), an event called de novo telomere addition. How this activity is suppressed remains unclear. Combining single-molecule imaging and deep sequencing, we show that the budding yeast telomerase RNA (TLC1 RNA) is spatially segregated to the nucleolus and excluded from sites of DNA repair in a cell cycle-dependent manner. Although TLC1 RNA accumulates in the nucleoplasm in G1/S, Pif1 activity promotes TLC1 RNA localization in the nucleolus in G2/M. In the presence of DSBs, TLC1 RNA remains nucleolar in most G2/M cells but accumulates in the nucleoplasm and colocalizes with DSBs in rad52Δ cells, leading to de novo telomere additions. Nucleoplasmic accumulation of TLC1 RNA depends on Cdc13 localization at DSBs and on the SUMO ligase Siz1, which is required for de novo telomere addition in rad52Δ cells. This study reveals novel roles for Pif1, Rad52, and Siz1-dependent sumoylation in the spatial exclusion of telomerase from sites of DNA repair.

The principal role of Ku in telomere length maintenance is promotion of Est1 association with telomeres.

Telomere length is tightly regulated in cells that express telomerase. The Saccharomyces cerevisiae Ku heterodimer, a DNA end-binding complex, positively regulates telomere length in a telomerase-dependent manner. Ku associates with the telomerase RNA subunit TLC1, and this association is required for TLC1 nuclear retention. Ku-TLC1 interaction also impacts the cell-cycle-regulated association of the telomerase catalytic subunit Est2 to telomeres. The promotion of TLC1 nuclear localization and Est2 recruitment have been proposed to be the principal role of Ku in telomere length maintenance, but neither model has been directly tested. Here we study the impact of forced recruitment of Est2 to telomeres on telomere length in the absence of Ku's ability to bind TLC1 or DNA ends. We show that tethering Est2 to telomeres does not promote efficient telomere elongation in the absence of Ku-TLC1 interaction or DNA end binding. Moreover, restoration of TLC1 nuclear localization, even when combined with Est2 recruitment, does not bypass the role of Ku. In contrast, forced recruitment of Est1, which has roles in telomerase recruitment and activation, to telomeres promotes efficient and progressive telomere elongation in the absence of Ku-TLC1 interaction, Ku DNA end binding, or Ku altogether. Ku associates with Est1 and Est2 in a TLC1-dependent manner and enhances Est1 recruitment to telomeres independently of Est2. Together, our results unexpectedly demonstrate that the principal role of Ku in telomere length maintenance is to promote the association of Est1 with telomeres, which may in turn allow for efficient recruitment and activation of the telomerase holoenzyme.

Mutually exclusive binding of telomerase RNA and DNA by Ku alters telomerase recruitment model.

In Saccharomyces cerevisiae, the Ku heterodimer contributes to telomere maintenance as a component of telomeric chromatin and as an accessory subunit of telomerase. How Ku binding to double-stranded DNA (dsDNA) and to telomerase RNA (TLC1) promotes Ku's telomeric functions is incompletely understood. We demonstrate that deletions designed to constrict the DNA-binding ring of Ku80 disrupt nonhomologous end-joining (NHEJ), telomeric gene silencing, and telomere length maintenance, suggesting that these functions require Ku's DNA end-binding activity. Contrary to the current model, a mutant Ku with low affinity for dsDNA also loses affinity for TLC1 both in vitro and in vivo. Competition experiments reveal that wild-type Ku binds dsDNA and TLC1 mutually exclusively. Cells expressing the mutant Ku are deficient in nuclear accumulation of TLC1, as expected from the RNA-binding defect. These findings force reconsideration of the mechanisms by which Ku assists in recruiting telomerase to natural telomeres and broken chromosome ends. PAPERCLIP:

Live cell imaging of telomerase RNA dynamics reveals cell cycle-dependent clustering of telomerase at elongating telomeres.

The telomerase, which is composed of both protein and RNA, maintains genome stability by replenishing telomeric repeats at the ends of chromosomes. Here, we use live-cell imaging to follow yeast telomerase RNA dynamics and recruitment to telomeres in single cells. Tracking of single telomerase particles revealed a diffusive behavior and transient association with telomeres in G1 and G2 phases of the cell cycle. Interestingly, concurrent with telomere elongation in late S phase, a subset of telomerase enzyme clusters and stably associates with few telomeres. Our data show that this clustering represents elongating telomerase and it depends on regulators of telomerase at telomeres (MRX, Tel1, Rif1/2, and Cdc13). Furthermore, the assay revealed premature telomere elongation in G1 in a rif1/2 strains, suggesting that Rif1/2 act as cell-cycle dependent negative regulators of telomerase. We propose that telomere elongation is organized around a local and transient accumulation of several telomerases on a few telomeres.