REGULATION OF HIPPOCAMPAL CONNECTIVITY BY NEUROD2 MEDIATED TRANSCRIPTION

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 发育中的大脑中神经回路的组装被认为需要遗传决定和活动依赖机制。许多由神经活动介导的长期变化依赖于钙激活的新基因产物的转录。因此，钙激活的转录因子提供了一种机制，将外部信号与神经发育的遗传程序联系起来。NeuroD 2是一个基本的螺旋-环-螺旋转录因子，以前在我们的实验室分离，使用屏幕参与皮质发育的新型钙调节转录因子。NeuroD 2表达在海马中受到发育调节，在P7和P14之间达到峰值，与该结构中突触发生的初级阶段一致。在这里，我们展示了NeuroD 2介导的转录在苔藓纤维（MF）到CA 3连接的正常发育中的作用。在NeuroD 2基因敲除的小鼠中，其具有大体上正常的脑结构，MF传入神经的钙结合蛋白染色显示主MF束的远端部分显著且优先减少。虽然纤维束延伸到CA 3区的全长，但它未能详细说明被称为CA 3区的特征性增大。 端球在其远端尖端。MF通路中突触前末梢的TIMM染色显示，该通路中突触形成的减少相似，如果不是更大的话。通过荧光黄染料注射的CA 3锥体神经元的突触后形态分析揭示了接收MF输入的近端顶端树突的特征性多头棘的类似减少。有趣的是，KO中更远端的经典棘的大小和密度不受影响。这提出了一种可能性，即虽然MF连接的发展需要NeuroD 2介导的转录，但来自其他通路的突触可能以NeuroD 2独立的方式形成。这些研究开始定义一种新的转录途径，调节海马回路主要兴奋性成分中连接的发展。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The assembly of neural circuits in the developing brain is thought to require both genetically determined and activity-dependent mechanisms. Many of the long-term changes mediated by neural activity are dependent on calcium-activated transcription of new gene products. Thus, calcium-activated transcription factors provide a mechanism for linking extrinsic signals with genetic programs of neural development. NeuroD2 is a basic helix-loop-helix transcription factor previously isolated in our lab, using a screen for novel calcium-regulated transcription factors involved in cortical development. NeuroD2 expression is developmentally regulated in the hippocampus, peaking between P7 and P14, coincident with the primary period of synaptogenesis in this structure. Here, we demonstrate a role for NeuroD2 mediated transcription in the normal development of mossy fiber (MF) to CA3 connectivity. In NeuroD2 null mice, which have grossly normal brain structure, calbindin staining of the MF afferents revealed a dramatic and preferential reduction in the distal portion of the main MF bundle. Although the fiber tract extends the full length of the CA3 region, it fails to elaborate the characteristic enlargement known as the ¿¿end bulb¿¿ at its distal tip. TIMM staining for pre-synaptic terminals in the MF pathway revealed a similar, if not greater, reduction in synapse formation in this pathway. Analysis of post-synaptic morphology of CA3 pyramidal neurons by Lucifer Yellow dye injection revealed a similar reduction in the characteristic multi-headed spines of the proximal apical dendrites receiving MF input. Interestingly, the size and density of the more distally located classical spines was not affected in the KO. This raises the possibility that while NeuroD2 mediated transcription is required for the development of MF connectivity, synapses from other pathways onto the same neuron may form in a NeuroD2 independent manner. These studies begin to define a novel transcriptional pathway regulating the development of connectivity in a major excitatory component of hippocampal circuitry.