Dissecting molecular elements of threat behavior

总结 动物具有对其环境中的威胁做出反应的内在能力，但其潜在机制是 不太了解。全面了解这些复杂的压力诱发行为需要 所有参与神经元的特征、它们的连接以及它们与其他组织的相互作用 （包括肠道、循环系统、肌肉等的交感连接）。然而，这个水平 在复杂的脊椎动物中很难进行分析。一种理性的方法是分析这些 更简单的无脊椎动物模型中的过程。该提案旨在了解神经机制 在无脊椎动物模型系统中对威胁响应（行为和生理）进行编码。线虫， 秀丽隐杆线虫，提供了一个独特的机会来分析调节基因、细胞和电路 复杂的行为。 Chalasani 实验室开发了一种新颖的威胁行为模型，其中涉及 秀丽隐杆线虫和第二种捕食性线虫物种Pristionchus pacificus之间的相互作用。一个挨饿的 太平洋对虾将在 30 分钟内攻击并吞噬秀丽隐杆线虫。线虫反过来试图避开 P. pacificus 及其分泌物。 Chalasani 实验室描述了一种新颖的冗余神经回路，可以检测 P. 太平洋捕食者并驱动快速回避行为，这需要逆转运动，然后是 广角转弯。除了这种快速回避之外，实验室还发现线虫暴露于 捕食者的分泌物在很长一段时间（30分钟）内表现出运动减慢（冻结），卵子减少 产蛋行为，以及在多个组织中诱导线粒体应激。这些响应最多持续 1 个 捕食者线索被移除后一小时，这让人想起在其他捕食者身上观察到的防御行为—— 猎物模型。一项试点基因筛选鉴定出seb-3（促肾上腺皮质激素释放因子的秀丽隐杆线虫同源物） 受体 1 (crfr1)) 是这些长期行为和生理变化所需的。这是第一个 有证据表明，CRF 信号传导会影响行为和生理机能以应对外部威胁 无脊椎动物。此外，细胞培养测定系统用于鉴定同源配体 NLP-49，该配体 激活 SEB-3 受体。在这里，将使用遗传方法来表征 CRF 所发挥的作用 协调行为和生理变化以应对外部威胁的信号。目标1将 探究 CRF 信号传导成分（SEB-3 受体、NLP-49 配体和其他潜在的 配体）驱动捕食者介导的行为变化。底层的神经回路将被绘制出来。在 目标 2，神经元中的 CRF 信号传递到其他组织，从而导致诱导的机制 线粒体应激，将被确定。在目标 3 中，将进行重点遗传筛查以识别 CRF 信号通路的其他成分负责应激诱导的行为和 生理变化。这些研究将揭示神经回路和CRF信号通路如何过程 有关环境威胁的信息，以产生适应性应激反应。

Summary Animals have an intrinsic ability to respond to threats in their environments, but the underlying mechanisms are poorly understood. A complete understanding of these complex stress-induced behaviors requires the characterization of all participating neurons, their connections, and their interactions with other tissues (including sympathetic connections in the gut, the circulation system, muscles, etc.). However, this level of analysis is difficult to achieve in complex vertebrate organisms. One rational approach is to analyze these processes in simpler invertebrate models. This proposal aims to understand the neural mechanisms that encode threat responses (both behavioral and physiological) in an invertebrate model system. The nematode, Caenorhabditis elegans, provides a unique opportunity to analyze the genes, cells, and circuits that regulate complex behaviors. The Chalasani lab has developed a novel model of threat behaviors that involves interactions between C. elegans and a second predatory nematode species, Pristionchus pacificus. A starving P. pacificus will attack and devour a C. elegans in 30 minutes. C. elegans in turn, seeks to avoid P. pacificus and its secretions. The Chalasani lab has characterized a novel, redundant neural circuit that detects the P. pacificus predator and drives rapid avoidance behavior, which entails a reversal in locomotion followed by a wide-angle turn. In addition to this rapid avoidance, the lab also discovered that C. elegans exposed to predator secretions for a long period of time (30 minutes) exhibit slowed locomotion (freezing), reduced egg- laying behavior, and the induction of mitochondrial stress in multiple tissues. These responses last up to one hour after the predator cue is removed, and are reminiscent of defensive behaviors observed in other predator- prey models. A pilot genetic screen identified seb-3 (the C. elegans homolog of corticotrophin releasing factor receptor 1 (crfr1)) as required for these long-term behavioral and physiological changes. This is the first evidence that CRF signaling affects behavior and physiology in response to an external threat in an invertebrate. Additionally, a cell culture assay system was used to identify a cognate ligand, NLP-49, that activates the SEB-3 receptor. Here, genetic methods will be used to characterize the role played by CRF signaling in coordinating behavioral and physiological changes in response to an external threat. Aim 1 will probe the role of CRF signaling components (the SEB-3 receptor, the NLP-49 ligand, and other potential ligands) in driving predator-mediated behavioral changes. The underlying neural circuits will be mapped. In Aim 2, the mechanism by which CRF signaling in neurons is relayed to other tissues, resulting in the induction of mitochondrial stress, will be determined. In Aim 3, a focused genetic screen will be performed to identify additional components of the CRF signaling pathway that are responsible for stress-induced behavioral and physiological changes. These studies will reveal how neural circuits and the CRF signaling pathway process information about environmental threats to generate adaptive stress responses.