Bidirectional Tyrosine Kinase Signaling

描述（由申请人提供）：海马体是大脑中维持增殖细胞供应的两个主要区域之一，这些细胞能够在成年期产生新的神经元。在这里，海马体齿状回（DG）亚颗粒带（SGZ）中的自我更新干细胞和瞬时扩增祖细胞分裂、短距离迁移，并分化成新的颗粒细胞神经元，整合到现有的大脑回路中。尽管人们认为新产生的神经元可能参与学习和记忆，但调控干细胞/祖细胞迁移、增殖、分化以及最终突触整合到大脑中的因素尚不清楚。EphB1和EphB2受体酪氨酸激酶在胚胎和出生后发育以及成人大脑的海马干/祖细胞中表达。利用基因靶向小鼠进行的体内研究表明，EphB1和更深层的EphB1+EphB2的缺失会导致发育中的DG中巢蛋白阳性的干细胞/祖细胞数量减少。能够填充DG的突变干细胞/祖细胞表现出细胞过程极性缺陷，细胞体在正常SGZ生态位之外的异位定位，以及增殖增加。我们的数据支持这样一种假设，即通过与其同源的ephrin-B跨膜配体相互作用，EphB受体将重要信号转导到海马干细胞/祖细胞中，以控制它们在DG形成过程中的迁移，以及在成年期SGZ继续产生新生神经元时的迁移。为了进一步验证我们的想法，我们将：(1)确定EphB受体在海马发育过程中用于控制干细胞/祖细胞迁移的细胞内信号机制；(2)使用条件策略删除成熟海马干细胞/祖细胞中的EphB受体，以确定这些分子如何在成人大脑中特异性调节神经母细胞行为。提出的研究将提供一个更好的理解干细胞生物学和细胞间的相互作用和生化信号在发挥作用。进一步预期，这项工作将导致我们对正常大脑中调节神经发生的信号机制的理解取得进展。这可能为我们学习和储存记忆能力背后的分子基础提供重要的见解。最后，由于海马体损伤和干细胞增殖/迁移的相关变化可由多种病理引起，因此拟议的研究也可能为未来的干细胞治疗提供新的分子靶点，以治疗患有神经系统疾病、变性或损伤的个体。公共卫生相关性：海马体是大脑中参与学习和记忆的主要中心，是成人大脑中含有干细胞的两个区域之一。目前的研究主要集中在Eph受体酪氨酸激酶，它在海马干细胞上表达，并发挥转导对正常干细胞迁移和增殖模式重要的化学信号的功能。预计这项研究将导致我们对发育和成人大脑中干细胞分子调控的理解取得进展，并可能为我们如何学习和储存记忆提供见解。此外，由于海马体损伤可导致干细胞增殖的变化，该研究还可能为未来的干细胞治疗提供新的分子靶点，以治疗患有神经系统疾病、变性或损伤的个体。

DESCRIPTION (provided by applicant): The hippocampus is one of two major areas in the brain that maintains a supply of proliferating cells that are able to produce new neurons well into adulthood. Here, self-renewing stem and transient-amplifying progenitor cells in the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG) divide, migrate a short distance, and differentiate into new granule cell neurons that integrate into the existing circuitry of the brain. Although it is thought the new neurons generated may participate in learning and memory, the factors that regulate stem/progenitor cell migration, proliferation, differentiation, and eventual synaptic integration into the brain are not well understood. The EphB1 and EphB2 receptor tyrosine kinases are expressed in hippocampal stem/progenitor cells during embryonic and postnatal development as well as in the adult brain. In vivo studies using gene targeted mice show that deletion of EphB1 and more profoundly EphB1+EphB2 results in a reduced number of nestin-positive stem/progenitor cells that populate the developing DG. Mutant stem/progenitor cells that do manage to populate the DG exhibit defective polarity of cell processes, ectopic positioning of cell bodies outside of the normal SGZ niche, and increased proliferation. Our data leads to the hypothesis that, upon interaction with their cognate ephrin-B transmembrane ligands, the EphB receptors transduce important signals into hippocampal stem/progenitor cells to control their migration during development as the DG forms and later during adulthood as the SGZ continues to give rise to newborn neurons. To further test our ideas we will: (1) determine the intracellular signaling mechanisms that EphB receptors use to control the migration of stem/progenitor cells during development of the hippocampus, and (2) use conditional strategies to delete EphB receptors in stem/progenitor cells of the mature hippocampus in order to determine how these molecules may regulate neuroblast behaviors specifically in the adult brain. The proposed research will provide a better general understanding of stem cell biology and the cell-cell interactions and biochemical signals that are at play. It is further anticipated that this work will lead to advances in our understanding of the signaling mechanisms that regulate neurogenesis in the normal brain. This may provide important insight into the molecular basis behind our ability to learn and store memories. Finally, as damage to the hippocampus and associated changes in stem cell proliferation/migration can result from numerous pathologies, the proposed research may also provide novel molecular targets for future stem cell therapies to treat individuals suffering from neurological diseases, degeneration, or injury. PUBLIC HEALTH RELEVANCE: The hippocampus is a major center of the brain involved in learning and memory and is one of the two areas in the adult brain that contain stem cells. The studies proposed focus on Eph receptor tyrosine kinases which are expressed on hippocampal stem cells and function to transduce chemical signals that are important for normal stem cell migration and proliferation patterns. It is anticipated this research will lead to advances in our understanding of the molecular regulation of stem cells in the developing and adult brain, and may provide insight into how we learn and store memories. Furthermore, as damage to the hippocampus can lead to changes in stem cell proliferation, the proposed research may also provide novel molecular targets for future stem cell therapies to treat individuals suffering from neurological diseases, degeneration, or injury.