Cell-biological mechanisms directing primary cilium mediated control of neuron polarisation

神经元的一个关键特征是它们对周围组织的信号做出反应的能力，这使得它们能够区分自己的前部和后部，从而实现极化。发育中的胚胎脊髓中的新生神经元会脱落它们的尖端以移动到它们的最终位置。这种脱落事件的结果是，这些新生神经元失去了决定它们极性的关键蛋白质，以及它们的细胞天线，即初级纤毛，它使这些细胞能够感知周围组织的外部信号。因此，新生神经元停止对Shh信号的反应并退出细胞周期，这是神经元分化的关键步骤。在此之后，神经元必须迅速重建其极性。这一步是至关重要的，因为它允许神经元延长一个被称为轴突的长细胞过程，轴突与目标细胞（如肌肉或其他神经元）建立联系。在发育中的胚胎中，神经元对周围组织的外部信号作出反应而分化。这些外部信号决定了这种极化的方向，从而决定了轴突移动的方向，或者它是否形成。因此，这是一个至关重要的事件，对功能性神经回路的形成至关重要。我们最近发现，新生神经元在准备延伸轴突时，会迅速重组新的初级纤毛。这个新的初级纤毛现在允许新生神经元改变对Shh信号的反应，Shh信号现在决定轴突投射的方向。本研究旨在研究细胞生物学机制，通过重组的初级纤毛来解释Shh信号。此外，我们还旨在研究通过重组的初级纤毛的信号传导如何指导神经元细胞骨架的重塑，以产生特征的神经元形态。为了实现这一目标，我们将使用尖端的显微镜技术来拍摄发育中的胚胎中极化神经元的电影，并将这些电影与固定胚胎组织的超分辨率荧光成像相结合。这将使我们能够识别和调节介导细胞对Shh信号反应的开关的机制，以及这如何影响分化神经元的细胞骨架重塑。这项工作可能会导致新的临床干预措施的发展，以促进这一过程在神经发育障碍的情况下或在成年期损伤。

A key feature of neurons is their ability to respond to cues from the surrounding tissues which allow them to distinguish their front from their back and thus achieve polarisation. Newborn neurons in the spinal cord of the developing embryo shed their tips to move to their final location. As a result of this shedding event, these newborn neurons lose the key proteins that define their polarity as well as their cellular antenna, called the primary cilium, which allows these cells to sense external cues from the surrounding tissues. Consequently, newborn neurons stop responding to Shh signalling and exit the cell cycle, which is a key step of neuronal differentiation. Following this, the neuron must now rapidly re-establish its polarity. This step is crucial, as it allows the neuron to extend a long cell-process, called an axon, which makes connections with its targets, such as muscles or other neurons. In the developing embryo, the neuron polarises in response to external cues from the surrounding tissue. These external cues determine the orientation of this polarisation and therefore determine the direction in which the axon will travel, or if it forms at all. This is thus a critical event that is essential for the formation of functional neuronal circuitry. We have recently discovered that newborn neurons quickly reassemble a new primary cilium as they prepare to extend an axon. This new primary cilium now allows the newborn neuron to switch its response to Shh signalling, which now acts to determine the direction in which the axon projects. This proposal aims to investigate the cell biological mechanisms that direct this switch in the interpretation of Shh signalling by the reassembled primary cilium. Furthermore, we also aim to investigate how signalling through the reassembled primary cilium directs remodelling of the neuronal cytoskeleton to generate the characteristic neuronal morphology. To achieve this, we will use cutting-edge microscopy techniques to make movies of polarising neurons in developing embryos and combine these with super-resolution fluorescence imaging of fixed embryonic tissue. This will allow us to identify and modulate the mechanisms that mediate the switch in the cellular response to Shh signalling and how this influences cytoskeletal remodelling in differentiating neurons. This work may lead to the development of novel clinical interventions to promote this process in the case of neurodevelopmental disorders or following injury during adulthood.