Qiang Lu - US grants

DESCRIPTION (provided by applicant): The long-term objective of this application is to understand the mechanisms that control the growth and maintenance, differentiation, and migration of neural progenitor cells in the mammalian cerebral cortex. During development, neurons of the cerebral cortex arise from neural progenitor cells in the neuroepithelium, also called the ventricular zone. Neural progenitor cells initially grow within the ventricular zone. As corticogenesis proceeds, they differentiate into neurons, which migrate out of the ventricular zone into their final residence in the cortical plate. How the decision of growth vs. differentiation is made during this developmental progression of corticogenesis is largely unknown. Our preliminary studies identified the ephrin-B reverse signaling pathway as a candidate system in regulation of this choice point. Ephrin-B is the transmembrane ligand of the Eph receptor tyrosine kinases. Ephrins and Ephs are distinctive in that they mediate bi-directional signaling in many cell-cell interactions-a typical forward signal by Ephs and a unique reverse signal through ephrins. In the developing mouse cerebral cortex, ephrin-B1 and its downstream signaling effector protein PDS-RGS3 are specifically co-expressed in neural progenitor cells. Blocking ephrin-B1 expression results in outward migration of the affected neural progenitor cells into the cortical plate, most likely as a result of differentiation. The current study will further investigate this novel mechanism of control in neural progenitor cells. The specific aims include: (1) characterize the temporal and spatial expression patterns of ephrin-Bs and their cognate EphB receptors in relation to neural progenitor cells in the mouse cerebral cortex; (2) define the role of ephrin-B1 in growth vs. differentiation, and determine the contribution of the reverse signaling pathway in this function of ephrin-B1; and (3) investigate the mechanisms that control the expression of ephrin-B1 in neural progenitor cells. These studies are expected to contribute to our understanding on the development of the cerebral cortex and should help in improving the effectiveness of using neural progenitor/stem cells in cell replacement therapy.

DESCRIPTION (provided by applicant): The goal of this study is to understand how epigenomic modifications in neural stem/progenitor cells contribute to the control of a dynamic balance between the state of self-renewal and differentiation, a fundamental question of developmental biology that has a direct implication for improving our understanding of the mechanisms of brain development and the possible etiology of developmental or behavioral brain disorders. This will be done by characterizing the changes of global DNA and chromatin state during neurogenesis in brain development. Our approach will be aided by the development and validation of a novel genetic strategy for isolation of endogenous neural progenitor cells. In this genetic system, neural progenitor cells and their immediate neuronal progeny are differentially marked by the expression of two reporters, thereby allowing prospective co-isolation of these two cell types and providing an endogenous source of father- daughter cells suitable for comparative genome-wide epigenetic profiling. Using this genetic system, we will purify neural progenitor cells and progeny from the developing mouse cerebral cortex, characterize differential patterns of DNA methylation and histone modification between these two cell types, identify the marks that correlate with cell type-specific expression patterns of the modified genes, and explore the potential function of these marks in the regulation of cortical neurogenesis using established in vivo functional assays. We anticipate that this study will provide a comprehensive map of the epigenetic state of neural progenitor cells during neurogenesis, identify epigenetic marks potentially crucial for neural progenitor cell fate specification, as well as help identify pathological alterations in the epigenome which may lead to developmental and behavioral brain disorders.

DESCRIPTION (provided by applicant): Neural stem/progenitor cell study offers novel avenues for understanding the etiology and for developing potential treatment of many developmental and behavioral brain disorders and brain cancers. At the center of the study is how a delicate balance between the two key states of stem/progenitor cells, the self-renewal state and differentiation state, are maintained by intrinsic and extrinsic mechanisms in development and in adult life, because a defect in this homeostasis of neural stem/progenitor cells causes malformation of the brain and may even lead to tumor formation. Research over the past decade has thus far uncovered dozens of genes that are important for this regulation by either promoting self-renewal or stimulating differentiation, however, this progress represents only the beginning of our understanding on this fundamental stem cell biology issue. In this application, we propose to systematically and comprehensively characterize genes that are specifically expressed in neural progenitor cells and use this information to further identify causal factors crucial for the control of neural progenitor homeostasis. Our rationale is that by knowing the relevant factors involved in this process, we will be in a better position to elucidate the mechanisms that help specify the self-renewal and differentiation state of neural progenitor cells. To this end, we have developed a novel genetic two reporter system that enables isolation of endogenous neural progenitor cells and their direct progeny from the developing mouse brains. The purified neural progenitor cells and progeny will allow us to perform comparative gene expression analyses to identify differentially expressed genes. By identifying and characterizing these differentially expressed genes, we expect to uncover key regulators of neural progenitor homeostasis. This will ultimately help understand what and how equilibrium of molecular interactions in neural progenitor cells guides the balance between self-renewal and differentiation and how dysregulation in individual molecular axis may lead to a particular pathological condition in brain disorders.

? DESCRIPTION (provided by applicant): Neural progenitor cells maintain a tight control of the balance between self-renewal and differentiation in the developing and adult brains and can respond to environmental cues to either switch on more proliferation or produce more differentiated cells. Such a homeostatic control is not only important for normal development but also critical for proper functioning of the brain. The long-term goal of our study is to understand how self- renewal and differentiation are regulated during brain development and to apply the obtained knowledge for developing better diagnostic tools and novel therapeutic approaches for treating developmental brain disorders and brain cancers. This application proposes to investigate a novel protein interaction network that is crucial for controlling symmetric (self-renewal) versus asymmetric (differentiation) cell division in neural progenitor cells. In our previous studies, we have demonstrated, using combined cellular, embryological, and genetic approaches, that the regulator of G protein signaling (RGS)-mediated ephrin-B reverse signaling pathway is essential for maintaining the neural progenitor cell state in the embryonic cerebral cortex and that the Ga subunit signaling pathway is important for activating neuronal differentiation. We have identified a mitotic kinesin that can interact with and recruit the ephrin B/RGS proteins into the midbody of dividing neural progenitor cells, suggesting that the role of the ephrin-B/RGS pathway in neural progenitor cell regulation is linked to cytokinesis, the final stage of cell division. In addition, we have recently identified several interacting proteins of th active Ga subunits and found that these proteins, similar to G? subunit, could activate neurogenesis. We thus propose to further characterize the biochemical interaction of the ephrin-B/RGS/mitotic kinesin and Ga subunit interaction network and examine the potential function of these networks in shaping neural progenitor cells' decision to either divide symmetrically or asymmetrically. We anticipate that the data obtained from this study will ultimately help understand what and how molecular interactions in neural progenitor cells guides the balance between self-renewal and differentiation and how dysregulation in these networks may lead to certain developmental brain disorders or tumorigenesis.