Extrinsic signals required for maintenance of dendrite coverage

描述（由申请人提供）：树突树突模式是神经元类型的标志，也是神经元功能的关键决定因素，影响神经元可以接收的输入类型和数量，以及神经元处理多个输入的能力。随着动物的成长，许多神经元的树突必须按比例扩大，以维持适当的连接，并维持其接受野的覆盖范围。同样，成年神经元的大部分树突在很长一段时间内保持稳定，以维持接受野的覆盖和连接模式。然而，人们对树突乔木是如何积极维持的知之甚少。使用基因筛选，我们已经确定了突变，表型上定义了果蝇感觉神经元树突维持的不同外部调节模式。通过这一提议，我们旨在验证以下假设：(1)局部粘附接触确保树突及其感受野在生长期间的协调扩张；(2)基质来源信号限制树突结构可塑性，阻止树突生长超出正常的感受野边界；(3)基质来源营养信号持续需要支持树突维持。在Aim 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。我们将使用基于遗传编码的荧光接近传感器在体内监测这些接触，使用电子显微镜在高分辨率下表征接触，通过改变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基因突变。在目标2中，我们将定义基质细胞外基质（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来描述正常发育和维持缺陷突变体中ECM组织和分布的变化。此外，我们将确定ECM修改所需的底物衍生因素。在Aim 3中，我们将定义一个神经元非自主通路，调节树突维持的营养信号。总之，这些研究将阐明在生长过程中树突及其底物协调生长的机制，确保树突覆盖的维持。尽管树突形态缺陷与多种发育和退行性疾病有关，包括智力迟钝、癫痫、精神分裂症和帕金森病，但人们对树突乔木是如何维持的知之甚少。从这项工作中获得的基本见解有望对理解不同类型的外部信号在树突维持中的正常发育作用以及干扰这些外部信号的后果具有重要意义。

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.