Control of Astrocyte Development and Astrocyte-Synapse Interactions

星形胶质细胞是高度复杂的细胞，具有数十万个细小的突起， 包裹神经元突触这些突触周围的星形胶质细胞过程积极参与突触 通过调节神经递质释放，维持离子稳态， 调节突触连接。尽管星形胶质细胞在突触发育和功能中的重要性， 我们对控制复合物形成的分子和细胞机制知之甚少， 星形胶质细胞形态和星形胶质细胞-突触相互作用。 在我们的初步实验中，我们发现在小鼠视觉皮层中， 复杂的星形胶质细胞形态是一个发育调节过程，发生在一个时期， 广泛的突触形成视觉体验的操纵，即前三个期间黑暗饲养小鼠 周的出生后发展，强烈阻碍皮质星形胶质细胞的发展，表明经验- 突触连接的依赖性变化可以改变星形胶质细胞的形态成熟。怎么样 复杂的星形胶质细胞形态获得和重塑？为了解决这个问题，我们 开发了一种原代皮层神经元和星形胶质细胞共培养系统，该系统利用了以下优点 基本观察：自身培养的星形胶质细胞具有简单的成纤维细胞样形态;然而， 与神经元的接触，即使是很短的一段时间，也足以引发对神经元的广泛阐述。 星形胶质细胞星形胶质细胞的这种形态转变主要是由直接的神经元接触驱动的，而不是由 可溶性分泌因子使用该系统，我们进行了基于候选人的遗传筛查， 神经连接素（NL）家族细胞粘附分子（CAM）、NL 1、NL 2和NL 3的星形胶质细胞表达， 在体外和体内控制神经元粘附和星形胶质细胞的形态成熟。基于这些 研究结果，我们的目标是确定NLs在星形胶质细胞发育和星形胶质细胞- 突触相互作用为此，我们将测试三个假设：1）星形胶质细胞NLs控制星形胶质细胞 形态复杂性通过介导星形胶质细胞突触协会。2)NL通过以下方式执行这些功能： 它们与轴突/突触前神经毒素的细胞外相互作用和3）通过它们的关键细胞内结构域 控制星形胶质细胞内细胞骨架动力学。 这些研究有可能显着推进我们的分子基础的理解， 星形胶质细胞发育和星形胶质细胞-突触相互作用。此外，这里获得的结果将提供 关键的新途径，研究形成的三方突触，并揭示了一个新的范式，通过 星形胶质细胞NLs控制大脑发育，这一过程可能在神经系统中严重受损。 混乱！

Astrocytes are highly complex cells with hundreds of thousands of fine processes that contact and ensheathe neuronal synapses. These perisynaptic astrocyte processes actively participate in synaptic development and function by regulating neurotransmitter release, maintaining ion homeostasis, and modulating synaptic connectivity. Despite the importance of astrocytes in synaptic development and function, we know very little about the molecular and cellular mechanisms that control the establishment of complex astrocyte morphology and astrocyte-synapse interactions. In our preliminary experiments, we found that in the mouse visual cortex the establishment of the complex astrocyte morphology is a developmentally regulated process that occurs during a period of extensive synapse formation. Manipulation of visual experience, i.e. dark rearing mice during first three weeks of postnatal development, strongly stunts cortical astrocyte development, indicating that experience- dependent changes in synaptic connectivity can alter morphological maturation of astrocytes. How is the complex astrocyte morphology attained and remodeled? To mechanistically address this question, we developed a primary cortical neuron and astrocyte co-culture system that takes advantage of the following basic observation: Astrocytes cultured by themselves have a simple fibroblast-like morphology; however, contact with neurons, even for a short period of time, is sufficient to trigger extensive elaboration of the astrocytes. This morphological shift in astrocytes is primarily driven by direct neuronal contact, but not by soluble secreted factors. Using this system, we conducted a candidate-based genetic screen and identified that the astrocytic expression of neuroligin (NL) family cell-adhesion molecules (CAMs), NL1, NL2 and NL3 control neuronal adherence and morphological maturation of astrocytes in vitro and in vivo. Based on these findings, our objective here is to determine the functions of NLs in astrocyte development and astrocyte- synapse interactions. To do so, we will test three hypotheses: 1) Astrocytic NLs control astrocyte morphological complexity by mediating astrocyte-synapse association. 2) NLs perform these functions via their extracellular interactions with axonal/presynaptic neurexins and 3) via their critical intracellular domains that control cytoskeletal dynamics within astrocytes. These studies have the potential to significantly advance our understanding of the molecular basis of astrocyte development and astrocyte-synapse interactions. Moreover, the results obtained here will provide critical new avenues for studying the formation of the tripartite synapses and reveal a new paradigm through which astrocytic NLs control brain development, a process that may be critically impaired in neurological disorders.!