Molecular mechanisms to organize neurons into circuits

人类行为的方方面面都依赖于数十亿个神经细胞与神经回路的精确连接。大脑连接始于胚胎，通过基因协调的程序建立神经元连接的蓝图。经验使这张地图精炼到了成年期。我的研究目标是确定指定神经回路组装的分子和细胞机制。我们的方法是识别存在于神经元表面的细胞识别分子，这些分子塑造和连接神经元，重点放在小鼠视网膜和大脑中的解剖学和基因可及电路上。被称为簇状原钙粘附素(Pcdhs)的识别分子大家族提供了一个巨大的分子代码，有可能分配给每个神经元一个唯一的Pcdh分子组合，或Pcdh代码。通过研究Pcdhs在视网膜星状爆发神经元中的作用，我们发现这种Pcdh编码在单个神经元水平上控制神经元的连接和树突分支的分布，这是一种被称为轴突自我回避的新现象。我们认为，通过表达不同的Pcdh编码，每个神经元通过表达相同的Pcdh编码来识别和避免自己的分支。我们称这种神经元为“自我/非自我识别”，它允许神经元将它们的分支分布在一个区域内，但与邻近的神经元相连。在这个方案中，我们将研究Pcdhs在神经元自我/非自我识别中的细胞和分子功能。对于目标1，我们使用先进的时间推移显微镜来研究Pcdh调节发育中神经元的树突生长和自我回避的机制。我们将测试Pcdh蛋白中哪些分子区域是这一过程所必需的，并阐明分子信号。对于我们的第二个目标，我们将操纵Pcdh成员的巨大多样性，并减少每个神经元可用的Pcdh组合，以了解这如何影响其他神经细胞类型的连接。我们还将研究由原钙粘附素编码提供的自我/非自我识别在大脑神经连接中的更广泛作用。拟议的研究将培养具有神经科学和分子生物学领域各种尖端、多学科研究技术的高素质人才，有望在加拿大做出重要的科学贡献和创新。通过在我的实验室接受培训，高素质的人员将走上在研究和其他领域取得成功的职业生涯的轨道。从长远来看，我的研究团队将为电路布线寻找新的分子识别机制，并检查它们与电路功能相关的重要性。这项工作将对理解单个神经元是如何连接的，神经元集合如何形成复杂的神经电路，以及错误的连接如何导致神经功能障碍做出重大贡献。

All aspects of human behaviour rely on precise wiring of billions of nerve cells into neural circuits. Brain wiring begins in the embryo, with genetically-coordinated programs that establish a blueprint of neuronal connectivity. Experience refines this map well into adulthood. The goal of my research is to identify molecular and cellular mechanisms that specify neural circuit assembly. Our approach is to identify cell recognition molecules presented at the surface of neurons that shape and wire neurons, with a focus on anatomically and genetically accessible circuits in the mouse retina and brain. The large family of recognition molecules called Clustered Protocadherins (Pcdhs) supply a massive molecular code with the potential of assigning each neuron has a unique Pcdh molecular combination, or Pcdh code. By studying the role of Pcdhs in starburst neurons that reside in the retina, we discovered that this Pcdh code controls the neuronal wiring and distribution of dendrite branches at the level of individual neurons, in a novel phenomenon called ‘neurite self-avoidance’. We propose that, by expressing different Pcdh codes, each neuron recognize and avoid their own branches through expression of the same Pcdh code. We call this neuron ‘self/non-self recognition’, which allows neurons to distribute their branches across a territory but connect with neighbouring neurons. In this proposal, we will investigate the cellular and molecular function of Pcdhs in neuron self/non-self recognition. For Objective 1, we use advanced, time-lapse microscopy to investigate the mechanism by which Pcdh regulate dendrite outgrowth and self-avoidance in developing neurons. We will test which molecular regions within Pcdh proteins that are necessary for this process, and elucidate the molecular signals. For our second objective, we will manipulate the large diversity of Pcdh members and reduce the possible Pcdh combinations available to each neuron to understand how this affects the wiring of other neuronal cell-types. We will also investigate broader roles for self/non-self recognition provided by the protocadherin code in neural wiring in the brain. The proposed research will lead to training of Highly Qualified Personnel with a variety of cutting-edge, multidisciplinary research technologies in neuroscience and molecular biology, promising to make important scientific contributions and innovations in Canada. By training in my lab, the Highly Qualified Personnel will be on track for successful careers in research and beyond. In the long-term, my research team will seek novel mechanisms of molecular recognition for circuit wiring and examine their importance in relation to circuit function. This work will make significant contributions towards understanding how individual neurons are wired, and how ensembles of neurons form complex neural circuits and how miswiring leads to neural dysfunction.