Fig. 4

Human endogenous retrovirus (HERV) expression patterns in pluripotent cells. a HERV-K transcription in human embryogenesis is initiated during embryonic genome activation at the eight-cell stage and remains until the blastocyst stage. Dashed lines indicate proposed expression of HERV-K [31]. HERV-H can only be detected in epiblast cells of the late blastocyst [25]. b After induction of induced pluripotent stem cell (iPSC) reprogramming, HERV-K and HERV-H are derepressed with distinct dynamics. HERV-K transcription reaches its peak shortly before cells are fully reprogrammed. HERV-K expression subsequently decreases in reprogrammed cells and is silenced in iPSCs [32]. HERV-H is highly expressed earlier during reprogramming compared with HERV-K [24]. Note: the time points shown are approximate due to technical differences between studies