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Telomere-Dependent and Telomere-Independent Roles of RAP1 in Regulating Human Stem Cell Homeostasis

ABSTRACT: RAP1 is well known as a telomere-binding protein; yet its functions in human stem cells remain unclear. Here we generated RAP1-deficient human embryonic stem cells (hESCs) by CRISPR/Cas9 and obtained RAP1-deficient human mesenchymal stem cells (hMSCs) and neural stem cells (hNSCs) via directed differentiation. In both hMSCs and hNSCs, RAP1 negatively regulated telomere length. In addition, RAP1 acted as a transcriptional regulator of RLEN by tuning the methylation status of its promoter region. Phenotypically, RAP1 deficiency resulted in enhanced self-renewal and delayed senescence in hMSCs rather than in hNSCs, suggesting a complex role of RAP1 in regulating lineage specific stem cell homeostasis. Altogether, these results indicate that RAP1 plays both telomeric and non-telomeric roles in regulating the homeostasis of human stem cells.

ORGANISM(S): Homo sapiens

PROVIDER: GSE122654 | GEO | 2018/11/20

REPOSITORIES: GEO

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Project description:Background. Telomeric small RNAs related to PIWI-interacting RNAs (piRNAs) have been described in various eukaryotes; however, their role in germline-specific telomere function remains poorly understood. Using a Drosophila model, we performed an in-depth study of the biogenesis of telomeric piRNAs and their function in telomere homeostasis in the germline. Results To fully characterize telomeric piRNA clusters, we integrated the data obtained from analysis of endogenous telomeric repeats, as well as transgenes inserted into different telomeric and subtelomeric regions. The small RNA-seq data from strains carrying telomeric transgenes demonstrated that all transgenes belong to a class of dual-strand piRNA clusters; however, their capacity to produce piRNAs varies significantly. Rhino, a paralog of heterochromatic protein 1 (HP1) expressed exclusively in the germline, is associated with all telomeric transgenes, but its enrichment correlates with the abundance of transgenic piRNAs. It is likely that this heterogeneity is determined by the sequence peculiarities of telomeric retrotransposons. In contrast to the heterochromatic non-telomeric germline piRNA clusters, piRNA loss leads to a dramatic decrease in HP1, Rhino, and trimethylated histone H3 lysine 9 in telomeric regions. Therefore, the presence of piRNAs is required for the maintenance of telomere chromatin in the germline. Moreover, piRNA loss causes telomere translocation from the nuclear periphery toward the nuclear interior but does not affect telomere end capping. Analysis of the telomere-associated sequences (TASs) chromatin revealed strong tissue specificity. In the germline, TASs are enriched with HP1 and Rhino, in contrast to somatic tissues, where they are repressed by Polycomb group proteins. Conclusions piRNAs play an essential role in the assembly of telomeric chromatin, as well as in nuclear telomere positioning in the germline. Telomeric arrays and TASs belong to a unique type of Rhino-dependent piRNA clusters with transcripts that serve simultaneously as piRNA precursors and as their only targets. Telomeric chromatin is highly sensitive to piRNA loss, implying the existence of a novel developmental checkpoint that depends on telomere integrity in the germline.

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Telomere-Dependent and Telomere-Independent Roles of RAP1 in Regulating Human Stem Cell Homeostasis

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