Knockout studies have shown that the polycomb gene Bmi-1 is important for postnatal, but not embryonic, neural stem cell (NSC) self-renewal and have identified the cell-cycle inhibitors p16/p19 as molecular targets. Here, using lentiviral-delivered shRNAs in vitro and in vivo, we determined that Bmi-1 is also important for NSC self-renewal in the embryo. We found that neural progenitors depend increasingly on Bmi-1 for proliferation as development proceeds from embryonic through adult stages. Acute shRNA-mediated Bmi-1 reduction causes defects in embryonic and adult NSC proliferation and self-renewal that, unexpectedly, are mediated by a different cell-cycle inhibitor, p21. Gene array analyses revealed developmental differences in Bmi-1-controlled expression of genes in the p21-Rb cell cycle regulatory pathway. Our data therefore implicate p21 as an important Bmi-1 target in NSCs, potentially with stage-related differences. Understanding stage-related mechanisms underlying NSC self-renewal has important implications for development of stem cell-based therapies. © 2007 Elsevier Inc. All rights reserved.
Fasano, C. A., Dimos, J. T., Ivanova, N. B., Lowry, N., Lemischka, I. R., & Temple, S. (2007). shRNA Knockdown of Bmi-1 Reveals a Critical Role for p21-Rb Pathway in NSC Self-Renewal during Development. Cell Stem Cell, 1(1), 87–99. https://doi.org/10.1016/j.stem.2007.04.001