ANTISILENCING OF PLP GENE EXPRESSION IN OLIGODENDROCYTES

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DESCRIPTION: Myelin is produced by oligodendrocytes in the CNS, and its role in propagation of the action potential along the axon has been well studied. Myelin is an extension of the glial cell's plasma membrane, however, it is biochemically very different. Part of this difference can be attributed to the composition of proteins specifically targeted to the myelin membrane. One of these proteins, the myelin proteolipid protein (PLP) together with its alternatively spliced isoform DM-20 accounts for about 50% of the total protein found in adult CNS myelin. The ratio of the two isoforms changes during development with expression of DM-20 occurring well before myelination, however, as development proceeds, PLP becomes the major isoform. Mutation in the PLP gene cause X linked dysmyelination and in humans has been associated with Pelizaeus-Merzbacher disease (PMD) and some types of spastic paraplegia (SPG-2). Some people with PMD show perturbations in PLP gene expression; cases of no expression (deletion of the gene) or overexpression have been described. Thus, accurate expression of the PLP gene is critical and elucidation of its regulation will be helpful in deciphering critical regulatory elements that are mutated in some PMD/SPG-2 patients. Furthermore, it is important to understand how the gene is regulated, to help promote the remyelination process in people with demyelinating diseases. Multiple Sclerosis the most common demyelinating disease, generally occurs in adult substantially after the myelination period. Since PLP gene regulation is developmentally controlled and expression of the gene decreases after the age of two in humans, it is fundamental the regulation of the PLP gene be understood. Preliminary results presented in this application suggest that the PLP gene expression in oligodendrocytes is regulated by interplay of silencing and antisilencing mechanisms mediated through elements located within the first intron. One of these elements appears to function as and antisilencer upon binding with its cognate DNA-binding protein and together they override repression mediated by negative regulatory elements located elsewhere in PLP intron 1. The overall objectives of this proposal are to identify the antisilencer and negative regulatory elements by deletion transfection analysis with PLP-lacZ fusion genes and to characterize the DNA binding protein which promotes antisilencing in oligodendrocytes by biochemical approaches. These studies will increase our knowledge of antisilencing as a novel means of gene regulation which has been described for only a few other genes.