Genetic dissection of cell-cell interaction in neuronal patterning in C. elegans

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Neurons typically have projections called neurites (axons and dendrites), which are connected with neighboring neurons or other cells to pass signals via special cell-cell junction called synapses. Neurons with branched neurites often arrange their neurites in a tiled pattern by avoiding neurites of their neighboring neurons to maximize coverage while minimizing the overlap with which the territory is innervated. Tiling is observed in many neurons including the somatosensory and visual system of both vertebrates and invertebrates. Despite the notion that each class of neurons utilizes various mechanisms to tile their neurites, little is known about the tiling mechanisms in most systems. The limitation of knowledge on how neurons interact with their neighboring neurons is largely due to the lack of techniques to systematically label individual neurons in living animals. Therefore, we are in need of developing new systems to study inter-neuronal interactions to fully understand the molecular machineries of neural pattern formation.***   I propose to tackle this issue using the nematode, Caenorhabditis elegans, as a model system. C. elegans provides numerous experimental advantages. For example, C. elegans has a simple nervous system that consists of only 302 neurons, a stereotyped cell lineage. Most important for this study, individual neurons can be visualized with cell-specific markers in living animals, making C. elegans a powerful genetic model system to study neuronal circuit assembly and architecture.***   By combining two cell-specific promoters and two fluorescent proteins, I generated a genetic marker that stably labels two neighboring motor neurons, DD5 and DD6. Both of these cells belong to the same class of D-type GABAergic motor neurons and tile their axons and dendrites with their neighboring DDs. Using this genetic marker strain, I propose to identify genes responsible for axonal/dendritic tiling, and conduct functional analyses of the isolated genes to understand the cellular and molecular mechanisms of tiling. Proposed research involves basic and advanced genetics, molecular biology, genomic analyses using next generation sequencing (NGS) technology and imaging with state-of-the-art microscopes. This research program will provide an excellent platform for students to experience basic and advanced technologies in diverse disciplines. ***   I believe this is a timely proposal considering the current enthusiasm and interest in studying mammalian brain structure and function. As molecular mechanisms regulating neuronal development and function are well conserved from C. elegans to mammals, the proposed program will identify fundamental mechanisms of how local inter-neuronal communication contribute to neural circuit assembly. The insights from a simple nervous system will help us understand the principles of neurodevelopment in the mammalian brain.**