ABSTRACT Neurons have an astonishing ability to maintain their integrity throughout an organism’s lifespan. Both the functional and structural integrity are required for neurons to carry out their biological and behavioral tasks. Disruption of neuronal integrity compromises brain function and can lead to a myriad of neurological and psychiatric disorders. To date, the molecular underpinnings for neurons to maintain integrity is unknown, largely due to the enormous complexity of the human brain. In this proposal, I aim to develop a strategy using the simple nervous system of the nematode C. elegans to identify molecular mechanisms required for neuronal integrity. My working hypothesis is that the endocytic protein FCHO-1 is essential for neurons to maintain both functional and structural integrity. Our preliminary data from electrophysiological analyses demonstrated a significant decrease of synaptic transmission in fcho-1 mutants. Consistent with compromised neuron activities, the fcho-1 mutant worms exhibit defects in the locomotion behavior. Importantly, my electronic microscopy experiments uncovered a fascinating and unexpected phenotype; neighboring neurons are abnormally connected to neighbors in the absence of FCHO-1. To understand how FCHO-1 protects neuronal integrity, I have designed experiments with two Specific Aims. Aim 1 will determine the role of FCHO-1 in protecting neurons from abnormally sharing their contents with neighbors. Decades of research have established that each type of neurons carries specialized contents such as proteins and signaling molecules, which allow neurons to perform distinct functions. My working hypothesis is that, in the absence of fcho-1, neurons lose structural integrity and fail to preserve their specialized contents. I predict that neurons will share their protein contents with neighbor cells due to damages of cellular boundaries. To monitor the impact of FCHO-1 on structural integrity (i.e., preventing neurons from abnormally exchange cellular contents with neighbor cells), I have developed a novel PAGEN assay (protease-assisted gene activation) to follow abnormal exchange of proteins between neurons. Aim 2 will elucidate the molecular mechanism by which FCHO-1 protects the structural integrity of neurons. My working hypothesis is that FCHO-1 is required for the recycling of adherens junction proteins at neuron-neuron boundaries. In support of this idea, I observed that, in fcho-1 mutants, the abnormal connections between neurons occur at protein dense regions reminiscent of adherens junctions. I expect that disruption of the endocytic protein FCHO-1 will impair the internalization of adherens junction proteins, which subsequently destabilizes cellular boundaries between neurons and their neighbors. I will examine the role of FCHO-1 dependent endocytic pathways using genetic analyses. Together, results generated from this study will uncover novel mechanisms for FCHO-1 to support neuron integrity. Eluc...