MYELIN BASIC-PROTEIN GENE-EXPRESSION IN NEURONS - DEVELOPMENTAL AND REGIONAL CHANGES IN PROTEIN TARGETING WITHIN NEURONAL NUCLEI, CELL-BODIES, AND PROCESSES

The myelin basic protein (MBP) gene is part of the golli-mbp gene comp lex. In mouse, the golli-mbp gene produces two families of mRNAs from different transcription start sites that generate either MBPs or golli proteins (which contain MBP sequences in addition to unique peptide s equences). In situ hybridization and immunocytochemical analyses indic ate that golli products are expressed in selected neuronal populations in postnatal mouse brain, in addition to oligodendrocytes, as shown e arlier. The principal subcellular location of golli proteins in neuron s was in axonal and dendritic processes. In a small subset of neurons, golli proteins were located in nuclei. With development and neuronal maturation, golli-mbp expression decreased and/or there was a striking shift in subcellular localization from nuclei and cell soma to the ce ll processes in specific neuronal populations. Golli protein was local ized in neurites of migrating cerebellar granule cells, but it shifted to a nuclear localization when the cells took up residence in the int ernal granule cell layer. In some regions, (e.g., olfactory bulb and c erebellum) golli proteins were expressed over the entire postnatal per iod examined (birth to 75 d). The unique patterns of developmental exp ression within individual populations of neurons, and the unusual shif t in subcellular localization of golli proteins with neuronal migratio n and maturation, suggest a complex regulation of this gene at both th e transcriptional and posttranslational levels. The data also suggest that the cellular function(s) of the golli proteins is very different from the structurally related MBPs.