Analysis of neuronal remodeling during transitions between reproductive live cycle and dauer stage in C. elegans

为了了解神经元信号的变化如何影响行为，神经元交流的分子细节必须与神经元的连接相结合。线虫是研究电线和功能是如何联系在一起的理想模式生物。与脊椎动物或昆虫相比，它的神经系统要简单得多，但仍然足够复杂，可以展示一系列有趣的、功能上截然不同的运动行为。最重要的是，线虫可以经历一个独特的、可逆的发展过渡到达尔阶段，这涉及到形态和行为的根本变化。我们的目标是解决线虫发育转变过程中神经元重塑如何影响功能的问题。解决这一挑战需要i)高分辨率的超微结构成像来识别Dauer和成人期之间的神经系统的差异，ii)细胞和系统水平上的神经系统的详细功能网络模型，以及iii)定量的行为实验来验证预测的网络输出并测试不同的假说。我们与海德堡EMBL的Schwab小组合作，获得了有关线虫中枢神经系统和前感觉器官的完整FIB-SEM(聚焦离子束扫描电子显微镜)数据集。然后，我们与多伦多大学的梅珍博士团队合作，手动跟踪并注释了连接体。在进一步的项目准备工作中，我们开发了自动图像分析工具来量化电子断层图像中的突触囊泡池，并训练人工神经网络来预测FIB-SEM数据中的细胞边界和细胞核。我们将根据P.Kollmannsberger的工作改进这些工具并将其与量化细胞和网络形态的算法相结合，然后将它们应用于新获得的图像数据集。然后，我们将采用和使用Dandekar小组开发的网络建模工具，基于这些数据集定量预测达乌尔幼虫和生殖生命周期阶段之间的运动行为差异。最后，我们将使用行为视频显微镜装置对模型预测进行实验探索。了解线虫神经系统在正常和Dauer阶段之间的快速转换过程中是如何变化的，可能会回答许多悬而未决的神经元发育和可塑性问题，并可能导致更好地理解一般情况下在不利环境条件下生存的生物学策略。

To understand how changes in neuronal signaling affect behavior, the molecular details of neuronal communication must be combined with neuronal connectivity. An ideal model organism to study how wiring and function are connected is the nematode C. elegans. Its nervous system is much simpler compared to vertebrates or insects, but still complex enough to exhibit a range of interesting and functionally distinct motor behavior. On top of that, nematodes can undergo a unique and reversible developmental transition to the dauer stage that involves radical changes in morphology and behavior. We aim to address the question how neuronal remodeling during developmental transitions in nematodes affects function. Solving this challenge requires i) high-resolution ultrastructural imaging to identify differences in the neuronal system between dauer and adult stages, ii) a detailed functional network model of the neuronal system on the cellular and systems level, and iii) quantitative behavioral experiments to validate the predicted network output and to test different hypotheses. We acquired a full FIB-SEM (Focused Ion Beam – Scanning Electron Microscopy) dataset of the central nervous system and anterior sensory organs of C. elegans dauer in collaboration with the Schwab group at EMBL Heidelberg. We then manually traced and annotated the connectome in collaboration with the group of Dr. Mei Zhen at the University of Toronto. In further preparator work for the project, we developed automated image analysis tools to quantify the synaptic vesicle pool in electron tomograms, and trained artificial neural networks to predict cell boundaries and nuclei in FIB-SEM data. We will refine and combine these tools with algorithms to quantify cell and network morphology based on work by P. Kollmannsberger and will then apply them to newly acquired image datasets. We will then adapt and use network modeling tools developed by the Dandekar group to quantitatively predict differences in motor behavior between dauer larvae and stages of the reproductive life cycle based on these datasets. Finally, we will explore the model predictions experimentally using a behavioral video-microscopy setup. Understanding how the nematode nervous system changes during the rapid transition between normal and dauer stages might answer many unsolved questions of neuronal development and plasticity and could lead to a better understanding of biological strategies to survive adverse environmental conditions in general.