shRNA knockdown of Bmi-1 reveals a critical role for p21-Rb pathway in NSC self-renewal during development

• Published in: Cell stem cell 2007-06, Vol.1 (1), p.87-99
• Main Authors: Fasano, Christopher A, Dimos, John T, Ivanova, Natalia B, Lowry, Natalia, Lemischka, Ihor R, Temple, Sally
• Format: Article
• Language: English
• Subjects: Animals; Cell Division; Cell Proliferation; Cyclin-Dependent Kinase Inhibitor p21 - physiology; Electroporation; Female; Mice; Nervous System - cytology; Nuclear Proteins - genetics; Nuclear Proteins - physiology; Polycomb Repressive Complex 1; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - physiology; Repressor Proteins - genetics; Repressor Proteins - physiology; Retinoblastoma Protein - physiology; RNA - genetics; Stem Cells - cytology
• ISSN: 1875-9777
• DOI: 10.1016/j.stem.2007.04.001

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.