Bidirectional Tyrosine Kinase Signaling

描述(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后产生新的神经元。在这里，海马齿状回(DG)颗粒下带(SGZ)的自我更新干细胞和瞬时放大前体细胞分裂、短距离迁移，并分化成新的颗粒细胞神经元，整合到大脑现有的回路中。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的海马干/祖细胞中表达，在成年脑中也表达。在体内使用基因靶向的小鼠的研究表明，EphB1和更深层次的EphB1+EphB2的缺失导致发育中的DG中巢蛋白阳性的干细胞/祖细胞的数量减少。确实设法填充DG的突变干/祖细胞表现出细胞突起的极性缺陷，细胞体异位定位在正常SGZ生态位之外，并促进增殖。我们的数据导致了这样的假设，即当EphB受体与它们的同源ePhin-B跨膜配体相互作用时，EphB受体将重要信号转导到海马干/祖细胞，以控制它们在发育过程中的迁移，随着DG的形成，以及成年后SGZ继续产生新生神经元。为了进一步检验我们的想法，我们将：(1)确定EphB受体在海马体发育过程中控制干/祖细胞迁移的细胞内信号机制；(2)使用条件性策略删除成熟海马干/祖细胞中的EphB受体，以确定这些分子可能如何调控特定于成人大脑的神经母细胞行为。拟议中的研究将提供对干细胞生物学以及细胞与细胞之间的相互作用和正在发挥作用的生化信号的更好的总体了解。进一步预计，这项工作将促进我们对调节正常大脑神经发生的信号机制的理解。这可能会为我们学习和存储记忆能力背后的分子基础提供重要的洞察。最后，由于海马体的损伤和干细胞增殖/迁移的相关变化可能由多种病理因素引起，这项拟议的研究还可能为未来的干细胞疗法提供新的分子靶点，以治疗患有神经系统疾病、变性或损伤的个体。与公共健康相关：海马体是大脑中参与学习和记忆的主要中心，也是成人大脑中包含干细胞的两个区域之一。这些研究建议将重点放在海马区干细胞上表达的Eph受体酪氨酸激酶，它的功能是传递对正常干细胞迁移和增殖模式至关重要的化学信号。预计这项研究将有助于我们理解干细胞在发育中和成年大脑中的分子调控，并可能为我们学习和存储记忆提供洞察力。此外，由于海马体的损伤可以导致干细胞增殖的变化，拟议的研究还可能为未来的干细胞疗法提供新的分子靶点，以治疗患有神经疾病、退行性疾病或损伤的个体。

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.