Neurons and glia, the operating units of the mature brain, are derived from neural stem cells (NSCs) largely during embryonic development. NSCs that give rise to neurons and glia in the cerebral cortex are particularly important to mammals as they ultimately generate the tissue that allows us to perform high-order cognitive tasks. Many neurodevelopmental disorders are caused by abnormalities in molecular and cellular machinery involved in various NSC functions. For example severe disruptions in generation and migration of new neurons can cause microcephaly and anencephaly, whereas milder developmental defects may result in imperfections in connectivity of neurons such as those becoming apparent in Autism spectrum and schizophrenia. The developmental timing of molecular and cellular signals that regulate cortical development are particularly important as temporally distinct insult may impact the cortex, activity in the brain, and behavior differentially. A number of defects associated with mechanisms that impact cytokinesis in NSCs underlie distinct diseases. Therefore understanding how stem cells divide, and what governs changes in their division during the course of brain development and NSC maturation is critical to understanding neurodevelopmental disorders. In the course of cortical development NSCs must maintain an extremely important balance in their cellular divisions. They must first expand their own pool through symmetric divisions, after which they must switch how they divide so that they can generate neurons and glia through asymmetric divisions. The current understanding of cellular and molecular mechanisms that regulate these important divisions remains fragmented and much remains to be discovered regarding master regulators of this process. We recently discovered a novel regulator of this process belongs to a family of zinc-finger specificity protein transcription factors, called Sp2. We found accumulation of stem cells at the expense of neurogenesis when we deleted the Sp2 gene only in NSCs of the developing cerebral cortex. In contrast overexpression of Sp2 rapidly pushes stem cells to delaminate from their epithelial home in the ventricular surface of the developing cortex, and precociously generate cortical neurons. We have discovered a number of intriguing cell biological themes that underlie the potent effects of Sp2 on NSCs, which we present in our preliminary data. With these findings, we propose to use a combination of state-of-the-art genetic mouse strains, cell and slice culture assays, live imaging protocols, biochemical assays, and mapping of RNA and protein landscapes that are Sp2-depenent to test the central hypothesis that Sp2-dependent transcription regulates the correct balance of proliferation and differentiation by regulating symmetric and asymmetric divisions of NSCs in the developing cerebral cortices. We provide preliminary evidence that Sp2 may carry out this critical function in NSCs through its interactions with known mechanisms and pathways of cell division. Thus, our study proposes to explore a novel mechanistic model that links molecular machineries that drive cytokinesis with asymmetric division of NSCs for production of neurons in the cerebral cortices. Potential for Broader Impact: Our approaches to understand how cortical stem cells divide symmetrically or asymmetrically have wide implications. Symmetric and asymmetric decisions in various stem cells are key to tissue development and regeneration throughout the body. Disruption of this balance in division of stem cells can lead to a range of pathological conditions from developmental retardation of tissues to oncogenesis. Therefore, undertaking the basic cellular mechanisms that control this key neural stem cell function is critical to understanding not only how appropriate divisions are controlled in stem cells during normal development, but also how their abnormal divisions in pathological conditions lead to devastating diseases such as cancer. Moreover, the mechanisms we study can be harnessed to better define and refine reprogramming strategies for generation of patient-specific stem cells, neurons, and glia and their potential therapeutic application in various brain diseases.
This research proposal explores the role of a novel molecular mechanisms utilized by neural stem cells which allows them to make a very important decision during their life; whether to make more of themselves (symmetric divisions) or to generate daughter cells that will become mature neurons (asymmetric divisions). Understanding and identifying novel regulators of this important decision in neural stem cells is critical for understanding normal brain development, as well as multiple neurodevelopmental disorders associated with mental retardation ranging from microcephaly to autism spectrum and schizophrenia. In so doing, our studies will further the prospects of cell-based therapies for neurodegenerative diseases.
