Neural stem cell self-renewal.

Two fundamental properties of stem cells are their ability to self-renew and to differentiate. Self-renewal is an integration of proliferation control with the maintenance of an undifferentiated state. Stem cell self-renewal is regulated by the dynamic interplay between transcription factors, epigenetic control, microRNA (miRNA) regulators, and cell-extrinsic signals from the microenvironment in which stem cells reside. Recent progress in defining specific roles for cell-intrinsic factors and extrinsic factors in regulating stem cell self-renewal starts to unfold the multilayered regulatory networks. This review focuses on cell-intrinsic regulators, including orphan nuclear receptor TLX, polycomb transcriptional repressor Bmi1, high-mobility-group DNA binding protein Sox2, basic helix-loop-helix Hes genes, histone modifying enzymes and chromatin remodeling proteins, and small RNA modulators, as well as cell-extrinsic signaling molecules, such as Wnt, Notch, Sonic hedgehog (Shh), TGFalpha, EGF, and FGF. Unraveling the mechanisms by which neural stem cells renew themselves will provide insights into both basic neurosciences and clinical applications of stem cell-based cell replacement therapies for neurodegenerative diseases.