PCGF6, a polycomb group protein, regulates mesodermal lineage differentiation in murine ES cells and functions in iPS reprogramming

Polycomb group (PcG) proteins comprise a large group of evolutionary conserved factors with essential roles for embryonic development and adult stem cell function. PcG proteins constitute two main multiprotein polycomb repressive complexes (PRC1 and PRC2) that operate in a hierarchical manner to silence gene expression. Functionally distinct PRC1 complexes are defined by Polycomb group RING finger protein (PCGF) paralogs. So far, six PCGF paralogs (PCGF1-6) have been identified but paralog-specific functions are not well understood. In our studies, we observed that Pcgf6 showed the highest expression level in undifferentiated murine embryonic stem cells (ESCs), blastocysts and testes. When ESCs differentiated, Pcgf6 expression strongly declined. To further investigate Pcgf6 biology, we established dox-inducible shRNA knockdown (KD) ESCs. Following Pcgf6 KD in ESCs the expression of pluripotency genes decreased, while mesodermal- and spermatogenesis-specific genes were de-repressed. Concomitantly with the elevated expression of mesodermal lineage markers, Pcgf6 KD ESCs showed increased hemangioblastic and hematopoietic activities. Finally, PCGF6 replaced SOX2 but not KLF4 or c-MYC in the generation of germline-competent iPS cells. Forced expression of Pcgf6 in OSKM-driven reprogramming increases iPS efficiency while Pcgf6 KD reduces the formation of ESC-like colonies. Together, these analyses show that Pcgf6 is non-redundantly involved in maintaining the pluripotent nature of ESCs and functions in iPS reprogramming. 6 samples were hybridized GeneChip Mouse Gene 1.0 ST Arrays (Affymetrix)