Antisilencing as a means of regulating myelin proteolipid protein gene expression in oligodendrocytes

Myelin is a multilamellar structure that surrounds axons and helps to facilitate neural transmission. In the central nervous system (CNS), a cell called the oligodendrocyte produces myelin. The composition of CNS myelin is relatively simple, with the myelin proteolipid protein (Plp) gene encoding the most abundant protein present in mature myelin. The Plp gene is expressed primarily in oligodendrocytes (although a few other cell types have been shown to express the gene) with peak expression coincident with the active myelination period. Transgenic mice that carry a Plp-lacZ fusion gene [PLP(+)Z] regulate the transgene in a manner consistent with the spatial and temporal expression of the endogenous Plp gene. PLP(+)Z contains murine Plp sequences extending from the proximal 2.4 kb of 5'-flanking DNA downstream to the first 37 bp of exon 2 driving expression of the bacterial reporter gene, lacZ. The goal of this dissertation was to identify elements contained within this portion of the Plp gene that help to regulate its expression in oligodendrocytes. Specifically, the role of Plp intron 1 DNA was examined by transfection analysis using constructs derived from PLP(+)Z, which contain partial or complete deletion of intron 1 sequences. Results presented in this dissertation demonstrate that the Plp gene in oligodendrocytes is regulated, at least partially, by several elements located within the first intron. One of these elements, which in fact is region that binds multiple proteins, functions as an antisilencer; it overrides the repression mediated by negative regulatory elements located elsewhere within the first intron. The antisilencer region was mapped between Plp intron 1 DNA positions 1,083 and 1,177 based on numbering the first intron from positions 1 to 8,140. Protein-DNA binding assays, including electromobility shift assays, DNase I footprinting, and antibody interference studies in addition to functional assays using site-specific Plp-lacZ mutated constructs suggest that the transcription factor AP-1 binds to the antisilencer region and is an important component of a higher ordered complex which is ultimately responsible for mediating the antisilencing process. The balance between repression and depression could be the means by which the temporal expression of the Plp gene is regulated.