Polycomb Group Protein Bmi1 Promotes Hematopoietic Cell Development from Embryonic Stem Cells

Abstract

Bmi1 is a component of the Polycomb repressive complexes and essential for maintaining the pool of adult stem cells. Polycomb repressive complexes are key regulators for embryonic development by modifying chromatin architecture and maintaining gene repression. To assess the role of Bmi1 in pluripotent stem cells and on exit from pluripotency during differentiation, we studied forced Bmi1 expression in mouse embryonic stem cells (ESC). We found that ESC do not express detectable levels of Bmi1 RNA and protein and that forced Bmi1 expression had no obvious influence on ESC self-renewal. However, upon ESC differentiation, Bmi1 effectively enhanced development of hematopoietic cells. Global transcriptional profiling identified a large array of genes that were differentially regulated during ESC differentiation by Bmi1. Importantly, we found that Bmi1 induced a prominent up-regulation of Gata2, a zinc finger transcription factor, which is essential for primitive hematopoietic cell generation from mesoderm. In addition, Bmi1 caused sustained growth and a >100-fold expansion of ESC-derived hematopoietic stem/progenitor cells within 2-3 weeks of culture. The enhanced proliferative capacity was associated with reduced Ink4a/Arf expression in Bmi1-transduced cells. Taken together, our experiments demonstrate distinct activities of Bmi1 in ESC and ESC-derived hematopoietic progenitor cells. In addition, Bmi1 enhances the propensity of ESC in differentiating toward the hematopoietic lineage. Thus, Bmi1 could be a candidate gene for engineered adult stem cell derivation from ESC.

Pcgf6, a Polycomb Group Protein, Regulates Mesodermal Lineage Differentiation in Murine ESCs and Functions in iPS Reprogramming

“…The Pcgf component of these PRC1 subtypes is of special interest as they define specific PRC1 functions indicated by genome‐wide chromatin binding . The expression of PRC1 complex components changes during ESC differentiation and consequently different PRC1 complexes with different subunit compositions assemble . In agreement we observed that upon ESC differentiation Pcgf6 expression ceased and alternative Pcgf paralogs become expressed.…”

The Polycomb Protein Ezh2 Impacts on Induced Pluripotent Stem Cell Generation

“…In our previous work, we showed that forced Bmi1 expression promotes hematopoietic cell development from ES cells [26]. We also found that Bmi1 can efficiently substitute for c-Myc in iPS cell generation (unpublished data).…”

“…ES cells (HM1) and iPS cells were cultured, as described previously [26,27]. Briefly, cells were maintained on inactivated MEF feeder layer from C57BL/6 mice with ES cell medium.…”

“…shRNA lentivirus vectors targeting Ezh2 were transfected into 293T cells with the packaging plasmids pCMVDR8.74 and pVSV-G, as described previously [26]. Transfections were with the calcium phosphate coprecipitation method.…”

Searching for the Key to Expand Hematopoietic Stem Cells

“…Other groups reported efficient generation of cells that mostly produce the myeloid lineage following long term engraftment or produce CD34+ hematopoietic precursors that have phenotype similar to adult HSC but might best correspond to the embryonic stage of yolk-sac, aortogonadalmesonephros (AGM), and/or fetal liver stage of hematopoiesis (Melichar et al, 2011;Narayan et al, 2006 andfor review : Tian andKaufman, 2008). More recently, the polycomb group protein Bmi1 was shown to promote more than 100-fold increase of hematopoietic cell development from ESC (Ding et al, 2011).…”