Wnt Singaling Pathway and Neural Stem Cell Fate Determination

Among the most important biological questions is how to regenerate new neurons in adult life in order to replace the lost neurons and restore the biological function of central nervous system (CNS) that has been halted by injury or disease. Central to answer this question is a profound understanding of the biology and behavior of neural stem cells (NSCs). Although the proliferation and differentiation of NSCs during early neural development has been widely studied, the fate determination of NSCs in _ad_u_lt, in the context of injury is poorly understood. My long-term goal is to understand the molecular mechanisms of NSCs fate determination and neurogenesis in _ad_u_lt brain and to apply this knowledge toward the repair of neural circuitry damaged by injury. The identification of populations of neural stem cells (NSCs) in the adult mammalian central nervous system raises the possibility of future repair of neuronal damage from brain and spinal cord injuries resulting from trauma or stroke, or neuronal loss from neurodegenerative diseases [1-5]. Cell-replacement strategies are of particular interest for diseases of the central nervous system, because, unlike many other tissues, the mature mammalian brain and spinal cord have a limited capacity for self-repair. Previously, we induced neurogenesis from endogenous NSCs in adult neocortex. \vhere it does not normally occur, by manipulating the microenvironment [6-8]. Recruitment of new neurons can be induced in a region-specific, layer-specific, and neuronal type-specific manner, and newly recruited neurons can form long-distance connections to appropriate targets [6, 7-12J. Recently, we studied the gene expression profiles of stem cells from different origins, including 1\SCs, using microarray, and found that Wnt signaling pathway components are highly expressed in NSCs [13J. Activation of the Wnt signaling pathway increases the proliferation and inhibits the differentiation ofNSCs isolated from the embryo in vitro [14]. Moreover, components of the Wnt signaling pathway, such as ~-catenin, are highly expressed in NSCs in _ad_u_lt mice brain including hippocampus, where newborn neurons are continuously being generated and added to the neural circuitry throughout adulthood. This suggests that the Wnt signaling pathway might also be involved in the regulation of NSC fate determination in the a_d_u_It hippocampus as well. The lethality of ~-catenin null mutants has restricted investigation of the role of the Wnt signaling pathway in the behavior of 1\SCs in postnatal brain. In preliminary work, I have successfully isolated and cultured NSCs from embryo, and studied the function of Wnt signaling pathway on NSCs fate determination in vitro by using the adenoviral expression system. In addition. we have analyzed a genetically modified mouse in which the Cre recombjnase specifically expresses in postnatal dentate gyrus. This mouse colony provides the possibility to spatially and cell-type specifically interrupt interested genes, including the \Vnt signaling pathway components, in postnatal dentate gyrus. Therefore, in the current application, I propose to use the mouse hippocampal dentate gyrus as a model system to study the NSC fate determination in adult mice brain. Progress in this research will advance our understanding of molecular mechanisms controlling expansion of the stem cell poo/' and/or promotion of neurogenesis from endogenous NSCs in _ad_u_lt brain, and may provide insight into the potential of NSCs for repairing damaged neural circuitry.