An increase in telomere sister chromatid exchange in murine embryonic stem cells possessing critically shortened telomeres

Abstract

Telomerase deficiency leads to a progressive loss of telomeric DNA that eventually triggers cell apoptosis in human primary cells during prolonged growth in culture. Rare survivors can maintain telomere length through either activation of telomerase or recombination-based telomere lengthening, and thus proliferate indefinitely. We have explored the possibility that telomeres may be maintained through telomere sister chromatid exchange (T-SCE) in murine telomere reverse transcriptase-deficient (mTert ؊/؊ ) splenocytes and ES cells. Because telomerase deficiency leads to gradual loss of telomeric DNA in mTert ؊/؊ splenocytes and ES cells and eventually to chromosomes with telomere signal-free ends (SFEs), we examined these cell types for evidence of sister chromatid exchange at telomeres, and observed an increase in T-SCEs only in a subset of mTert ؊/؊ splenocytes or ES cells that possessed multiple SFEs. Furthermore, T-SCEs were more often detected in ES cells than in splenocytes that harbored a similar frequency of SFEs. In mTert heterozygous (mTert ؉/؊ ) ES cells or splenocytes, which are known to exhibit a decrease in average telomere length but no SFEs, no increase in T-SCE was observed. In addition to T-SCE, other genomic rearrangements (i.e., SCE) were also significantly increased in mTert ؊/؊ ES cells possessing critically short telomeres, but not in splenocytes. Our results suggest that animals and cell culture differ in their ability to carry out genomic rearrangements as a means of maintaining telomere integrity when telomeres become critically shortened. murine telomerase reverse transcriptase ͉ telomere signal-free end

Association of telomere length with authentic pluripotency of ES/iPS cells

“…Short telomeres, however, greatly limit teratoma growth and developmental pluripotency. Telomerase and telomeres are important for proliferation of ESCs and other types of stem cells [15,18,21,[26][27][28]. In the absence of telomerase, the oncogene proteins, K-Ras, c-myc, and the anti-apoptotic survivin are highly expressed in teratomas.…”

PARP1 Is a TRF2-associated Poly(ADP-Ribose)Polymerase and Protects Eroded Telomeres

“…We previously demonstrated that mTert Ϫ/Ϫ ES cells were telomerase deficient and underwent progressive loss of telomeric DNA during continuous passages in culture, and their chromosome ends eventually lost detectable telomeric DNA (Liu et al, 2000Wang et al, 2005). A slight increase in PARP1 signals was observed at both telomeric and nontelomeric regions of chromosomes of Figure S3 and Table 2).…”

“…The implication of the TRF2-PARP1 relationship in vivo was shown from the observation that PARP1 colocalized with TRF2 (Liu et al, 2000Wang et al, 2005). e Each chromosome is counted for four ends; 0.2% (9 SFEs/1043 ϫ 4 chromosome ends) or 12.8% (526 SFEs/1025 ϫ 4 chromosome ends) of chromosome ends have SFEs in mTert Ϫ/Ϫ ES cells at p30 or p90, respectively.…”

Zscan4 promotes genomic stability during reprogramming and dramatically improves the quality of iPS cells as demonstrated by tetraploid complementation

“…Furthermore, colocalization of γ-H2AX and Trf1, indicative of telomere-induced DNA damage foci [28][29][30], was significantly reduced in OSKMZ-infected cells as compared to OSKM-infected cells ( Figure 2C). Because γ-H2AX is a marker for DSBs [31], we tested general sister chromatid exchange (SCE) [32,33] in reprogramming cells. As expected, the rates of spontaneous SCE in OSKMZinfected MEFs were lower than those in OSKM-infected MEFs during the reprogramming process ( Figure 2D and 2E).…”