Cellular mechanisms of morphological and synaptic plasticity in neurons
My lab is interested in the formation and maintenance of synapses in mammalian central nervous system (CNS). CNS synapses are specialized compartments connecting the pre- and post-synaptic membrane together in a highly dynamical manner by adhesion molecules. N-cadherin, one of the major adhesion molecules at the synapse, represents a unique class of self-interacting (homophilic) proteins which function in the form of oligomer under the physiological concentration of extracellular calcium. Based on its nature of calcium-dependent self-association and interacting with underlying F-actin cytoskeleton, N-cadherin is poised at transmitting signals bidirectionally to both sides of the synapse. Most interestingly, when extracellular calcium around the synaptic cleft undergoes drastic fluctuation upon neuronal activity, it is conceivable to detect measureable re-organization of N-cadherin oligomers. Therefore, N-cadherin is likely to play a crucial role in coupling structural re-organization with neuronal activity.
Recent advancement in microscopy and molecular neuroscience made it possible to study the spatiotemporal regulation of synaptic proteins. We are in the process of dissecting the complex regulation of synaptic N-cadherin. Details are as follow:
I. The dynamics and turnover of surface proteins in dendrites and spines.
The amount of surface N-cadherin directly impacts the strength of adhesion which dictates the physical connections between pre- and post-synaptic membrane across the synapse. However, little is known about the dynamics of surface N-cadherin during neuronal activity. We will monitor the surface N-cadherin behaviors in living heterologous cells and neurons. Moreover, we will investigate the underlying molecular and cellular mechanisms that regulate such behaviors in conjunction with monitoring neuronal activities.
II. Synaptic adhesion molecule communication and intracellular signaling.
The turnover¡Xcombination of endocytosis, recycling & degradation¡Xof N-cadherin is tightly regulated through intracellular signaling pathways. NMDA receptor influences the endocytosis of N-cadherin through the tyrosine phosphorylation of one of its binding protein, £]-catenin. We will utilize biochemical and live-cell imaging techniques to elucidate signaling molecules that involve in this process.
III. Cross-talk between synaptic adhesion and other cellular processes.
N-cadherin is a substrate of £^-secretase that the truncated form of N-cadherin can mediate the proteasome-dependent degradation of CBP (CREB binding protein). This suggests that N-cadherin directly participates in the process of protein degradation. We will investigate the specificity of N-cadherin in protein degradation and whether itself is also a substrate of proteasome by a series of biochemical, molecular and live-cell imaging experiments.