During development and throughout adulthood, the nervous system transforms sensory experience from the environment into changes in neuronal activity which, in turn, cause long-lasting alterations in synaptic connections and dendritic arborization. Disruption to this process can result in long-term undesirable neurological consequences. For example, altered synapse number and functional plasticity responses are hallmarks of a number of mental health disorders including depression and schizophrenia [1-3]. Despite the importance of activity-dependent processes in shaping neuronal architecture, little is known about the molecular mechanisms by which changes in neuronal excitability are translated into altered connectivity. Using an RNAi-based approach in cultured neurons, we identified the GTPase Rem2 as a novel regulator of excitatory synapse development [4, 5]. We have also demonstrated that Rem2 is a novel immediate early gene whose transcription is rapidly up-regulated in response to calcium influx via neuronal depolarization . Thus, Rem2 may represent a key molecule through which external stimuli mediate direct effects on neuronal connectivity. To test this hypothesis in the intact nervous system of a vertebrate model organism, I propose to knockdown Rem2 in pyramidal neurons in rodent visual cortex and perform in vivo two-photon imaging of the synaptic contacts and overall circuit plasticity of these neurons while modulating visual experience. This experience-dependent in vivo approach to identify the role of Rem2 in activity-dependent neural circuit development provides an excellent opportunity to increase our understanding of genetically encoded, activity- dependent neural circuitry. Through a unique collaboration between mentors with expertise in in vivo circuit analysis, synapse development, and the molecular biology of gene regulation, I will become an expert in an impressive array of experimental techniques which will allow me to probe the function of other activity- regulated genes in the intact nervous system in the future.
The underlying structure of individual neurons is important for proper information processing and cognition. This importance is highlighted in several neuropsychiatric diseases, which typically display altered dendritic spine morphologies, but the underlying molecular mechanisms that regulate these changes remain largely unknown. Rem2 is an activity-regulated small, GTPase and is an excellent candidate to investigate neuronal architecture remodeling in response to changes in network excitability.