Extrinsic signals required for maintenance of dendrite coverage

描述（由申请人提供）：树突树枝化模式是神经元类型的标志和神经元功能的关键决定因素，影响神经元可以接收的输入的类型和数量以及神经元处理多个输入的能力。随着动物的生长，许多神经元的树突必须成比例地扩张，以维持适当的连接并保持其感受野的覆盖。同样，成年神经元中的大部分树突乔木在长时间内是稳定的，以维持感受野覆盖和连接模式。然而，很少有人知道枝晶乔木是如何积极维护。使用遗传筛选，我们已经确定了突变体的表型定义不同的模式的外在调控树突维持在果蝇感觉神经元。通过这个提议，我们的目标是测试以下假设：（1）局部粘附接触确保生长期间树枝状突起及其感受野的协调扩张，（2）基质衍生的信号限制树枝状突起结构可塑性，防止树枝状突起生长超出正常的感受野边界，和（3）持续需要基质衍生的营养信号来支持树枝状突起的维持。在目标1中，我们将定义树突上皮接触在协调树突乔木和感受野扩张中的作用，并确定调节这些接触的因素。我们将使用遗传编码的基于荧光的接近传感器在体内监测这些接触，使用电子显微镜以高分辨率表征接触，通过修改上皮中接触部位的分布来测试接触的功能相关性，并分析可能破坏这些接触的遗传突变体。在目标2中，我们将定义底物细胞外基质（ECM）修饰在限制树突生长和确保维持感受野覆盖方面的作用。我们将使用遗传编码标记和电子显微镜描绘ECM组织和分布在正常发育和维护缺陷突变体的变化。此外，我们将确定ECM修饰所需的基质衍生因子。在目标3中，我们将定义一个神经元非自主通路，调节树突维持营养信号。总之，这些研究将阐明机制，其中生长的树突和他们的基板在生长过程中协调，确保维护的树突覆盖。尽管树突形态缺陷与多种发育和退行性疾病（包括精神发育迟缓、癫痫、精神分裂症和帕金森病）有关，但人们对树突乔木如何维持知之甚少。从这项工作中获得的基本见解，预计将有意义的理解的正常发育的作用，不同类型的外源性信号在树突的维护，以及干扰这些外源性信号的后果。

DESCRIPTION (provided by applicant): Dendrite arborization patterns are a hallmark of neuronal type and a critical determinant of neuronal function, influencing the type and number of inputs that a neuron can receive as well as the ability of a neuron to process multiple inputs. As animals grow, dendrite arbors of many neurons must expand proportionally to sustain proper connectivity and maintain coverage of their receptive field. Likewise, large portions of dendrite arbors in adult neurons are stable over extended periods of time to maintain receptive field coverage and patterns of connectivity. However, little is known about how dendrite arbors are actively maintained. Using genetic screens, we have identified mutants that phenotypically define different modes of extrinsic regulation of dendrite maintenance in Drosophila sensory neurons. With this proposal, we aim to test the hypotheses that (1) localized adhesive contacts ensure coordinated expansion of dendrites and their receptive field during times of growth, (2) substrate-derived signals restrict dendrite structural plasticity, preventing dendrite growth beyond normal receptive field boundaries, and (3) substrate-derived trophic signals are continuously required to support dendrite maintenance. In Aim 1, we will define roles of dendrite-epithelial contacts in coordinating dendrite arbor and receptive field expansion, and identify factors that modulate these contacts. We will monitor these contacts in vivo using a genetically-encoded fluorescence-based proximity sensor, characterize the contacts at high resolution using electron microscopy, test the functional relevance of the contacts by modifying the distribution of the contact sites in the epithelium, and analyze genetic mutants that likely disrupt these contacts. In Aim 2, we will define roles of substrate extracellular matrix (ECM) modification in restricting dendrite growth and ensuring maintenance of receptive field coverage. We will use genetically encoded markers and electron microscopy to delineate changes in ECM organization and distribution during normal development and in maintenance-defective mutants. Additionally, we will identify substrate-derived factors required for ECM modifications. In Aim 3, we will define a neuron non-autonomous pathway that regulates trophic signaling for dendrite maintenance. Altogether, these studies will elucidate mechanisms by which growth of dendrites and their substrate are coordinated during growth, ensuring maintenance of dendrite coverage. Although defects in dendrite morphology are associated with a variety of developmental and degenerative disorders, including mental retardation, epilepsy, schizophrenia, and Parkinson's disease, little is known about how dendrite arbors are maintained. Basic insights gained from this work are expected to be of significance for understanding the normal developmental role of different types of extrinsic signals in dendrite maintenance as well as the consequences of perturbing these extrinsic signals.