Telomerase-mediated telomere elongation from human blastocysts to embryonic stem cells

Abstract

High telomerase activity is a characteristic of human embryonic stem cells (hESCs), however, the regulation and maintenance of correct telomere length in hESCs is unclear. In this study we investigated telomere elongation in hESCs in vitro and found that telomeres lengthened from their derivation in blastocysts through early expansion, but stabilized at later passages. We report that the core unit of telomerase, hTERT, was highly expressed in hESCs in blastocysts and throughout long-term culture; furthermore, this was regulated in a Wnt-b-catenin-signaling-dependent manner. Our observations that the alternative lengthening of telomeres (ALT) pathway was suppressed in hESCs and that hTERT knockdown partially inhibited telomere elongation, demonstrated that high telomerase activity was required for telomere elongation. We observed that chromatin modification through trimethylation of H3K9 and H4K20 at telomeric regions decreased during early culture. This was concurrent with telomere elongation, suggesting that epigenetic regulation of telomeric chromatin may influence telomerase function. By measuring telomere length in 96 hESC lines, we were able to establish that telomere length remained relatively stable at 12.0261.01 kb during later passages (15-95). In contrast, telomere length varied in hESCs with genomic instability and hESC-derived teratomas. In summary, we propose that correct, stable telomere length may serve as a potential biomarker for genetically stable hESCs.

Epigenetic Regulation of Telomere Maintenance for Therapeutic Interventions in Gliomas

“…Telomere length in stem cells is established long enough during embryogenesis to ensure tissue homeostasis but short enough to limit cell proliferation capacity and cancer initiation [14]. Such optimal telomere length is observed in human embryonic stem cells that demonstrate stable telomere length important for genomic stability [15]. The mechanism controlling telomere length in human embryonic and induced pluripotent stem cells involves active telomere trimming in addition to elongation by telomerase activity [16].…”

A balance between elongation and trimming regulates telomere stability in stem cells

“…During embryogenesis, telomere length is established such that long telomeres can support extended series of regulated cells divisions during the developmental program, but short enough to limit cell proliferation in the adult to suppress cancer initiation 21 . The stable telomere length found in human embryonic stem cells (hESCs) 22 , suggests that defined mechanisms have evolved to promote the optimal telomere length that ensures genomic stability.…”

Role of telomeric repeat–containing RNA in telomeric chromatin remodeling during the early expansion of human embryonic stem cells

“…Moreover, telomerase-dependent telomere lengthening was required in the reprogramming processes of iPSCs (14) and somatic cell nuclear transfer in ESCs (15). Elongated telomeres were observed in hESCs and mESCs compared with the inner cell mass of blastocysts, which is realized as a part of epigenetic reprogramming to pluripotency (16,17). A previous study demonstrated that high telomerase activity was critical for telomere lengthening during the early expansion of hESCs (17).…”

“…Elongated telomeres were observed in hESCs and mESCs compared with the inner cell mass of blastocysts, which is realized as a part of epigenetic reprogramming to pluripotency (16,17). A previous study demonstrated that high telomerase activity was critical for telomere lengthening during the early expansion of hESCs (17). Furthermore, remodeling of telomeric chromatin architecture was found to be associated with the extension of telomere DNA repeats, including decreased density of histone chromatin marker, H3k9me3/H4k20me3, and an increased level of telomere-capping protein telomeric repeat factor 1 (TRF1) (14,17).…”

“…A previous study demonstrated that high telomerase activity was critical for telomere lengthening during the early expansion of hESCs (17). Furthermore, remodeling of telomeric chromatin architecture was found to be associated with the extension of telomere DNA repeats, including decreased density of histone chromatin marker, H3k9me3/H4k20me3, and an increased level of telomere-capping protein telomeric repeat factor 1 (TRF1) (14,17). Recently, it was found that PSCs that lack the histone methyltransferase, Suv39h1/h2 (suppressor of variegation 3-9 homolog 1/2), which induced histone demethylation of telomere chromatin, demonstrated telomere elongation (18,19).…”