BRAIN EAGER: Novel Targeting Strategies for Projection-specific Mapping of Neurons

神经科学的一个中心目标是根据特定神经元的活动和连通性来理解行为。解剖追踪已经揭示了大脑中的中尺度连接，但是这个数据集缺乏功能实用性，没有能力对与其他大脑区域具有特定连接的神经元进行行为研究。最近，一些技术进步使得这些类型的实验成为可能，包括重新设计的病毒以特定的神经元类型为目标，并传递感兴趣的基因。这种方法很重要，因为特定神经元的基因靶向使人们能够在神经元的解剖结构（它投射到的区域）和功能（它编码的信息）之间建立联系。该项目将探索新工具的工程设计，这些工具将显著改善现有的逆行追踪技术，从而能够将行为功能映射到特定的神经元类型。由此产生的工具将广泛提供给社区，以增加其影响和效用。随着系统神经科学采用分子生物学的工具，人们越来越认识到电路特异性技术的重要性，例如，利用逆行病毒策略来定位由其投影定义的神经元类型，以进行解剖和遗传标记。这些工具对于使用遗传活性指示器进行细胞类型特异性记录或使用光遗传致动器进行控制至关重要。然而，现有逆行病毒的效率和可变向性（即不能靶向所有细胞类型）对这些实验方法提出了挑战。为了克服这一挑战，提出了两种方法来生成试剂，这些试剂将提供无毒的轮廓，同时最大限度地有效标记目标人群。这些方法将利用众所周知的病毒内化分子机制来克服趋向性，以及使用新的蛋白质连接技术改进的经典示踪剂。这些试剂将适用于精确和稳健的解剖跟踪，用于诱导光和化学发生致动器。因此，我们期望这些改进的试剂将允许更有效和更少变化的基于投影的靶向神经元分子货物，并促进新型的基于电路的映射实验。

A central goal in neuroscience is to understand behavior in terms of the activity and connectivity of specific neurons. Anatomical tracings have revealed the mesoscale connections in the brain, but this dataset lacks functional utility without the ability to behaviorally study neurons with specific connections to other brain regions. Recently, a number of technological advances have enabled these types of experiments, including re-engineered viruses to target specific neuron types and deliver genes of interests. This methodology is important because genetic targeting of specific neurons allows one to draw a link between a neurons's anatomy (the regions it projects to) and its function (the information it encodes). This project will explore the engineering of novel tools that will significantly improve existing retrograde tracing techniques and thereby enable mapping behavioral functions to specific neuron types. The resulting tools will be made broadly available to the community to increase their impact and utility.As systems neuroscience is adopting tools from molecular biology there is an increasing appreciation for the importance of circuit-specific technologies, for instance targeting neuron-types defined by their projections using retrograde viral strategies for anatomical and genetic labeling. These tools have been critical for cell-type specific recordings using genetic activity indicators, or control using optogenetic actuators. Nevertheless, the efficiency and variable tropism (i.e. inability to target all cell types) of existing retrograde viruses presents a challenge for these experimental approaches. To overcome this challenge, two methods are proposed to generate reagents that will provide a non-toxic profile while maximizing efficient labeling of the targeted population. The methods will exploit well-understood molecular mechanisms for viral internalization to overcome tropisms, as well as classic tracers improved using a novel protein ligation technique. These reagents will be suitable for precise and robust anatomical tracing, for induction of opto- and chemicogenetic actuators. Therefore we expect that these improved reagents will allow for more efficient and less variable projection-based targeting of neurons with molecular cargo and facilitate new types of circuit-based mapping experiments.