Study of the combined roles of Rb and p53 in the control of murine adult neurogenesis in vitro

Abstract

Adult neurogenesis (AN) is a highly dynamic process that is restricted to two main neurogenic zones in the brain, the sub-granular zone (SGZ) and the subventricular zone (SVZ). In the SVZ, activated adult neural stem and progenitor cells (aNSPCs) commit to differentiating into neuroblasts while migrating through the rostral migratory stream (RMS) to the olfactory bulb (OB) where they finally differentiate into GABAergic interneurons. This process requires high orchestration between cell cycling and cell death. This study aims at studying the combined roles of two main cell cycle regulators, the Retinoblastoma protein (Rb) and p53, during AN in the SVZ using inducible Nestin-CreERT2-YFP-transgenic mice and Rb-p53floxed-floxed mice. aNSPCs are regulated by extrinsic and intrinsic signals. Previous studies found that loss of p53 induced hyper-population of aNSPCs in the SVZ whereby p53 negatively regulates self-renewal of aNSPCs (Gil-Perotin et al. 2006; Meletis et al. 2006). More recently, we have studied the role of Rb during AN in the SVZ and showed that it mainly controls proliferation in adult neural progenitor cells (not stem cells). Thus, loss of Rb led to significant increase in the pool of progenitors resulting in a transient increase in OB neurogenesis. Moreover, Rb was necessary for the long-term survival of newborn neurons in the olfactory bulb (Naser et al. 2016). Knowing that neuronal loss in the absence of Rb might be mediated by p53-dependent mechanism(s), and that both Rb and p53 pathways have major crosstalk in the control of the cell cycle, we hypothesized that manipulation of both pathways through the combined deletions of these genes may help amplify the pool of aNSPCs and their progeny, and, might compensate for neuronal cell death of Rb-null newborn neurons inside the OB. Our results showed that the effects of Rb and p53 in the control of aNSPCs proliferation are indeed additive (synergistic) in culture, and, combined loss of both genes further increase the proliferative potential of these c