The long term goal of these studies is to establish the mechanism by which mutations affect the expression of myelin genes, and ultimately the development of the animal. The focus is on the myelin proteolipid protein (PLP) gene. This gene has unique cell-specific expression, and it is essential for normal nervous system function. Even conservative amino acid mutations in this protein are devastating to normal brain development. We believe that expression of this gene is controlled at the transcriptional and translational levels, and that mRNA stability is important for its overall control. The different dysmyelinating mutants provide models for several different kinds of changes in the control of myelin gene expression and oligodendrocyte differentiation. Unique changes in gene expression in the different mutants can be mediated by changes in RNA transcription, processing, stability or translatability. The proposed studies will provide important new information on the developmental regulation of this brain-specific gene, in normal and pathological conditions. Our specific studies will use the mutants to study the control of PLP gene expression by transcription or by mRNA stability. We will determine to what extent and how cell-specific control of PLP gene expression is regulated in normal mice. We hypothesize that much cell- specific control of transcription is localized at a distance from the promoter in the PLP gene, and we have identified an element in intron 1 that may increase the cell-specificity of this promoter. We will pursue this and other elements to determine their role in PLP gene expression in normal animals. We will determine how the downregulation of the PLP promoter is controlled in jimpy/msd mice, where it appears that protein sequence mutations reduce the transcription rate of this gene. Why is the promoter for this gene downregulated by the mutations, even apparently in peripheral nerve? We will study to what extent the PLP promoter is downregulated in jimpy/msd peripheral nerves, and how it is controlled, and we will study another, less severely affected PLP mutant, and determine PLP promoter activity in rumpshaker mice. We will determine if PbP promoter activity can be altered in an immortalized oligodendrocyte or in transgenic mice by overexpressing a mutated PLP or DM2O cDNA. Lastly, we will determine how PLP mRNA stability is controlled in normal and quaking. Our previous studies in transgenic animals suggest that PLP mRNA stability is important for PLP gene expression. We will identify which part of PLP mRNA is important for stability, what proteins bind to the mRNA, and whether PLP mRNA stability is altered in quaking mice.
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