The role of the extracellular matrix in establishing Schwann cell polarity

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Abstract Various cell types establish polarity to generate complex morphology and exert function. Schwann cells (SCs) are polarized with an adaxonal membrane facing the axon and a basolateral membrane facing the extracellular matrix (ECM). Previous work established that known polarity proteins, Par-3 and LKB-1/Par-4, localize to the adaxonal membrane prior to myelination and are required within SCs for the timely progression of myelination and Remak bundle formation. Although SC polarity is critical for proper peripheral nerve development, the mechanism for establishing polarity within SCs remains unknown. The basal lamina, a specialized structure of the ECM that abuts the basolateral membrane, is believed to be important for regulating polarity; additionally, in other epithelial cells collagen-IV is necessary for the establishment of polarity. SCs secrete collagen-IV into the basal lamina and express integrin alpha2, a collagen-IV receptor also known for its role in polarity. Therefore, I hypothesize that collagen-IV initiates SC polarity by signaling through integrin alpha2 and is necessary for rSC polarity but dispensable for myelination. I test this possibility by analyzing the role of SC secreted collagen-IV on peripheral nerve development, determining whether collagen-IV within the SC basal lamina is necessary and sufficient for SC polarity, and identifying the SC binding partner for collagen-IV. Preliminary data suggests that SC-secreted collagen-IV is important for timely myelination and Remak bundle formation. These results phenocopy those observed when polarity is disrupted by knocking out LKB1 specifically from SCs. Upon completion, this study will have important implications on the integration of extrinsic signals from the ECM onto the internal cell state. Thereby regulating polarity, which is critical for peripheral nerve health. Additionally, understanding the results and mechanisms of polarity defects can inform the understanding of peripheral neuropathies. In order to perform these studies, I will learn various techniques including protein biochemistry, including Western blot and co-immunoprecipitation, primary cell culture techniques, CRISPR- based gene editing, mouse behavioral assays, and viral construction/purification/transduction under the guidance of my sponsor Dr. Jonah Chan. I will receive additional training of career development skills such as experimental design, presenting posters/presentations, manuscript writing, and manuscript reviewing through my sponsor, classes within the UCSF Neuroscience Program, and workshops through UCSF Office of Career and Professional Development. I am confident that the rigorous training I receive during my PhD at UCSF will enable me to pursue my long-term goal of becoming a tenure track principal investigator within academia.