Dystroglycan regulates cerebellar synapse function

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Project Summary Dystroglycan is a scaffolding molecule composed of a transmembrane beta subunit and a non-covalently bonded extracellular alpha subunit. The alpha subunit undergoes heavy glycosylation and it is through these glycan chains that Dystroglycan forms protein-carbohydrate interactions with extracellular binding partners. A failure to properly glycosylate Dystroglycan results in a form of muscular dystrophy termed dystroglycanopathy. The muscular defects seen in dystroglycanopathies are often accompanied by neurological defects. While the role of Dystroglycan in muscle integrity has been well described, its role in the neurological aspects of the disease remains understudied. It is known that Dystroglycan in neuroepithelial cells is necessary for the proper migration of neurons during development, but Dystroglycan remains at high levels throughout life, suggesting a role beyond development. It has been shown that neuronal Dystroglycan co-localizes with certain markers of inhibitory synapses and can interact with neurexins, a well described class of presynaptic scaffolding molecules in the brain. Together, this suggests a potential role for Dystroglycan in the development of a subset of inhibitory synapses, acting as a postsynaptic scaffolding molecule. Recent work has shown that Dystroglycan in pyramidal neurons of the hippocampus is required for the function of a subset of inhibitory basket synapses, but other brain regions remain unexplored. This study will focus on inhibitory synapses in the cerebellum, where Dystroglycan is present at particularly high levels in Purkinje neurons. The proposed experiments will utilize mouse genetics, imaging, and slice physiology to dissect the mechanism by which Dystroglycan promotes synapse formation and/or maintenance of inhibitory synapses in cerebellar cortex. Aim 1 will identify the subset of synapses at which Dystroglycan is present and will describe the importance of Dystroglycan in the function of these synapses. Aim 2 will then seek to dissect the role of Dystroglycan in synapse formation and maintenance and will test the feasibility of gene therapy to rescue the observed synaptic phenotype. Aim 3 will investigate the roles of the various domains of Dystroglycan in synapse function: intracellular signaling from the C-tail of the beta subunit and the interaction with extracellular binding partners via glycosylation of the alpha subunit. This work will be among the first to explore the in vivo functional role of Dystroglycan at synapses in the brain. Furthermore, these experiments will provide understanding with regards to how defects in Dystroglycan results in cognitive deficits in human patients suffering from dystroglycanopathies and will aid in the development of gene therapies to treat such cognitive defects.