Critical role of transient activation of human endogenous retroviruses during reprogramming toward pluripotency

ABSTRACT: We recently showed that some human induced pluripotent stem cell (iPSC) clones were defective in neural differentiation and were marked with the activation of long term repeats (LTRs) of human endogenous retroviruses (HERVs). We herein demonstrated that these LTRs were transiently overexpressed during the generation of iPSCs and contributed to reprogramming. When the generation of iPSCs was completed, LTRs were re-suppressed to levels similar to those in human ES cells. However, differentiation-defective iPSC clones maintained high LTR expression levels, which indicated that these clones failed to complete reprogramming. lincRNA-RoR, a long intergenic non-coding RNA (lincRNA) that was previously shown to support the induction and maintenance of pluripotency, was detected among the LTR-driven transcripts. Short hairpin RNAs against the conserved sequence in LTRs or lincRNA-RoR markedly reduced the efficiency of iPSC generation. Reprogramming factors including OCT3/4, SOX2, and KLF4 bound to most LTRs. The expression of KLF4 was low in normal iPSC clones, but remained high in differentiation-defective clones. The forced expression of KLF4 in human embryonic stem cells led to the activation of LTRs and defects in neural differentiation. These results demonstrated that the transient overexpression of KLF4/LTR/lincRNA-RoR played crucial roles in reprogramming toward pluripotency in humans, whereas a failure in its re-silence resulted in differentiation defects. Four human induced pluripotent stem cell lines were subcloned into 55 separate lines. Bisulfite converted genomic DNA lysates from fibroblast, induced pluripotent stem cell, intermediate reprogrammed cell and embryonic stem cell lines were hybridized to Illumina HumanMethylation450 BeadChip.

ORGANISM(S): Homo sapiens

SUBMITTER: Kazutoshi Takahashi 

PROVIDER: E-GEOD-54848 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress