Mutations in L1CAM, the gene encoding the transmembrane multifunctional neuronal adhesion molecule L1, are associated with neurodevelopmental disorders including X-linked hydrocephalus and mental retardation. Some amino acid substitutions in various extracellular domains of L1 are known to affect posttranslational processing of the protein or its homophilic and heterophilic interactions. It is largely unknown, however, how these mutations result in neurodevelopmental disturbances and whether the effects of mutations on neurodevelopment can be modeled in vitro. We stably expressed full-length human wild type L1 and the known pathogenic missense mutations I179S, R184W, Y194C, and C264Y in NIH-3T3 cells. L1 protein synthesis, glycosylation pattern, and subcellular localization were analyzed. Neurite outgrowth of primary murine cerebellar neurons was measured after 23 hrs of co-cultivation using transfected NIH-3T3 cells as substrate. Like wild type L1, L1 protein with I179S or Y194C mutations was localized on the surface of the transfected substrate cells, but this was not the case with R184W or C264Y mutations. All four mutations were associated with reduced stimulation of neurite outgrowth. Measurement of neurite outgrowth on transfected substrate cells may be a suitable model for studying neurodevelopmental disturbances.
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