Crosstalk between neurotrophin and Wnt signaling pathways in neuronal development

描述（由申请人提供）：神经系统的正常功能依赖于精确神经元回路的建立。神经营养因子是由神经元目标分泌的细胞外指示信号，通过调节生存、生长和突触可塑性来影响神经系统的布线。尽管在理解目标来源的神经营养因子的功能方面取得了相当大的进展，但一个基本问题仍然存在：有限的神经营养因子及其受体如何协调建立和维持精确的神经元回路所需的各种事件？我们假设目标来源的神经营养因子影响神经元功能的一种机制是通过调节神经元表达和其他分泌生长因子的信号传导。神经营养因子和其他生长因子家族之间的这种串扰机制可能潜在地扩大神经营养因子在神经系统中的作用。我们最近发现了发育过程中神经营养因子和Wnt信号通路之间的相互作用。wnt是一大家族分泌的富含半胱氨酸的蛋白质，最初被认为是胚胎形成过程中的形态形成因子。然而，最近的研究发现wnt在神经元发育中具有令人惊讶的多种作用。本提案的总体目标是验证神经元中表达的wnt与其靶组织分泌的神经营养因子之间的相互作用调节神经元发育和精确神经元回路的建立的假设。因此，我们的具体目标是；(1)为了验证wnt的神经元表达受靶源性神经营养因子调节的假设：我们发现几种wnt及其受体在交感神经元中表达，交感神经元是研究神经元-靶相互作用的一个可处理的模型系统。其中，Wnt-5a在交感轴突到达最终目标的发育时期强烈表达。本研究的目的是证明Wnt-5a的神经元表达是通过与靶组织和靶源性神经营养因子的相互作用来调节的。(2)为了验证神经元wnt是交感神经元中神经营养因子功能介质的假设：我们发现Wnt-5a足以概括神经营养因子，神经生长因子（NGF）在培养的交感神经元中的生长促进作用。本研究的目的是证明Wnt-5a在NGF下游发挥作用，介导目标组织神经支配所需的轴突生长。(3)为了确定交感神经元中Wnt信号传导的机制：我们将描述交感神经元中将细胞外Wnt-5a信号耦合到轴突生长和分支所需的细胞骨架机制变化的信号转导机制。我们的研究将为神经元发育的分子机制提供新的见解，并为促进损伤或疾病后神经元的生长和再生提供新的策略。

DESCRIPTION (provided by applicant): The proper functioning of the nervous system relies on the establishment of precise neuronal circuits. Neurotrophins are extracellular instructive cues secreted by neuronal targets that influence wiring of the nervous system by regulating survival, growth and synaptic plasticity. Despite considerable progress in understanding functions of target-derived neurotrophins, a fundamental question still remains: How do a limited repertoire of neurotrophins and their receptors orchestrate the diverse events required to establish and maintain precise neuronal circuits? We hypothesize that one mechanism by which target-derived neurotrophins influence neuronal function is by regulating neuronal expression and signaling of other secreted growth factors. Such a mechanism of crosstalk between neurotrophins and other growth factor families could potentially broaden the repertoire of neurotrophin actions in the nervous system. We have recently identified an interaction between the neurotrophin and Wnt signaling pathways during development. Wnts are a large family of secreted cysteine-rich proteins, initially characterized as morphogens during embryonic patterning. However, recent studies identify surprisingly versatile roles for Wnts in neuronal development. The overall goal of this proposal is to test the hypothesis that interactions between Wnts expressed in neurons and neurotrophins secreted by their target tissues regulate neuronal development and establishment of precise neuronal circuits. Thus, our specific aims are; (1) To test the hypothesis that neuronal expression of Wnts is regulated by target-derived neurotrophins: We found that several Wnts and their receptors are expressed in sympathetic neurons, a tractable model system for studying neuron-target interactions. Of these, Wnt-5a is robustly expressed at a developmental time when sympathetic axons are reaching final targets. The goal of this aim is to demonstrate that neuronal expression of Wnt-5a is regulated by interactions with target tissues and target-derived neurotrophins. (2) To test the hypothesis that neuronal Wnts are mediators of neurotrophin function in sympathetic neurons: We found that Wnt-5a is sufficient to recapitulate the growth-promoting effects of the neurotrophin, Nerve Growth Factor (NGF), in cultured sympathetic neurons. The goal of this aim is to demonstrate that Wnt-5a functions downstream of NGF, to mediate axonal growth required for innervation of target tissues. (3) To identify mechanisms of Wnt signaling in sympathetic neurons: We will characterize the signal transduction machinery within sympathetic neurons that couples an extracellular Wnt-5a signal to changes in the cytoskeletal machinery necessary for axonal growth and branching. Our study will provide new insight into molecular mechanisms underlying neuronal development and allow for new strategies for promoting growth and regeneration of neurons following injury or disease.