Amy E. Ghiretti, Ph.D. - US grants

DESCRIPTION (provided by applicant): The overall structure and function of the central nervous system is established via a variety of carefully orchestrated processes, including the formation of synapses and the morphogenesis of the dendritic arborization of individual neurons. These processes are subject to influence by external factors, including the changes in neuronal activity that occur in response to the administration of drugs such as cocaine, amphetamines, nicotine, and opiates. Recently, the small GTPase Rem2 was identified as a novel regulator of excitatory synapse development, dendritic spine formation, and dendritic arbor morphology. Additionally, the ability of Rem2 to mediate dendritic morphology is dependent on Rem2 binding to calmodulin (CaM). Interestingly, Rem2 is upregulated at the transcriptional level in response to neuronal depolarization, suggesting that it can act as a direc link by which a neuron can respond to changes in activity by altering its structure and function as needed. This proposal seeks to explore the signaling mechanisms through which Rem2 mediates dendritic arborization in response to changes in neuronal activity both in vitro and in vivo. Specifically, an in vitro system of cultured rodent hippocampal neurons will be used to explore the interaction of Rem2 with CaM kinase II, as existing data suggests that Rem2 is downstream of this known regulator of dendritic morphology. To explore the role of Rem2 in such activity-dependent changes in morphology in vivo, the optic tectum of Xenopus laevis tadpoles, a well-characterized experimental system, will be used to identify how Rem2 participates in the morphological changes caused by activity in the form of visual sensory experience. Importantly, Rem2 is expressed in the striatum, which is the site of action of the reward attributes associated with drug addiction, as well as the hippocampus, which has been shown to undergo structural changes in response to amphetamines. Changes in CaM kinase signaling have also been extensively implicated in opiate addiction. Thus, a comprehensive study of the signaling pathways in which Rem2 is involved will provide new insights into how the underlying structure of the brain is altered to produce the functional changes associated with drug use and addiction. Ultimately, Rem2 may represent a key molecule through which external stimuli mediate direct effects on those signaling pathways that regulate the structure of individual neurons and the central nervous system as a whole. PUBLIC HEALTH RELEVANCE: The underlying structure of individual neurons and neuronal networks is carefully regulated to ensure the proper functioning of the central nervous system (CNS). However, many aspects of CNS structure are altered following the administration of drugs of abuse. I wish to explore the signaling pathways of Rem2, a novel protein that has been implicated in these same processes, to provide new insight into the mechanisms by which chronic drug abuse acts to change the structure of neurons. )

? DESCRIPTION (provided by applicant): Neurons are highly polarized cells, extending distinct processes specialized to send (axons) and receive (dendrites) information. The accurate trafficking of the correct protein cargoes to either the axonal or dendritic compartments is required to maintain this polarity and therefore proper neuronal function. This process is regulated by dynein and kinesin motor proteins that move along the microtubule cytoskeleton. Importantly, the mislocalization of protein cargos or dysfunction of microtubule and motor proteins is implicated in a number of neurological disorders, including neurodevelopmental disorders such as mental retardation and autism. While axonal trafficking is well studied due to the uniform polarity of axonal microtubules, dendritic microtubule structure is more complex; thus, the motors that mediate dendritic trafficking as well as the dynamics of dendritic microtubules themselves remain largely unknown. Several members of the kinesin-4 family have emerged as disease loci for a number of neurological disorders, including KIF4A (mental retardation), KIF21A (CFEOM1), and KIF21B (multiple sclerosis). Intriguingly, the closely related kinesin-4 family members KIF21A and KIF21B display distinct subcellular localization patterns despite their sequence homology. While KIF21A is preferentially trafficked to axons, KIF21B localizes to dendrites as well. Based on sequence gazing and preliminary data, we hypothesize that KIF21B plays a dual role in dendrites as a molecular motor and a regulator of dynamic microtubule remodeling. In this proposal, we will use single molecule assays and live imaging in rodent hippocampal neurons to fully characterize the function of KIF21B in dendrites. Our studies of KIF21B will help us to understand how the full repertoire of dendritic kinesins function to promote the functional specification of the dendritic and axonal compartments, and shed light on the little studied but essential process of dendritic trafficking, knowledge which is essential for our ability to develop effective therapeutics for neurodevelopmental disorders.