Regulation of murine myelin proteolipid protein gene expression

To identify putative sequences that direct cell type-specific expression and/or enhance proteolipid protein (PLP) gene expression, glial or nonglial cells were transfected with various PLP-luciferase constructs that collectively span the entire mouse PLP-specific DNA present in a transgene known to direct cell type specificity in transgenic mice. These constructs were transfected into murine oligodendrocyte cell lines that transcribe the PLP gene and, hence, should contain the requisite trans-acting factors necessary for PLP gene expression. Mouse NIH/3T3 fibroblasts were used as a nonglial model. We have finely mapped the PLP promoter region for transcriptional regulatory elements and demonstrate both positive and negative elements, none of which appear to extinguish expression in nonglial cells. The 5'-flanking PLP DNA tested did not enhance the basal herpes simplex-1 virus thymidine kinase (TK) promoter, nor did PLP sequences present in the distal half of intron 1. The 5' portion of intron 1 did enhance TK promoter activity, suggesting that this region of the gene may contain enhancer elements that modulate PLP gene expression; however, the enhancement did not appear to be cell type-specific. Intriguingly, a 541 bp region of the intron that significantly enhanced TK promoter activity contains multiple JC virus repeated elements and other elements known to be important in restricting the virus to oligodendrocytes. These results suggest that intron 1 sequences may modulate expression of the PLP gene.