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 the proteins specifically targeted to the myelin membrane. One of these proteins, the myelin proteolipid protein (PLP) accounts for almost 50% of the total protein found in adult CNS myelin. Expression of the gene is tightly regulated. In humans, mutations in the P/p gene (which resides on the X chromosome) have been shown to be associated the X-linked dysmyelinating disorder Pelizaeus-Merzbacher disease (PMD), and some types of spastic paraplegia (SPG-2). Dysmyelination can arise from either elevated levels of P/p gene expression or lack of expression. Thus accurate expression of the P/p is critical, and elucidation of its regulation will be helpful in deciphering essential transcription regulatory elements that may be mutated in some people with PMD/SPG-2. On the other hand, elucidation of the mechanisms whereby the gene is regulated could provide insight into alternative causes of PMD/SPG-2, which do not arise from P/p gene mutations. ? ? Furthermore, it is important to understand how the gone is regulated, in order to help promote the remyelination process in people with demyelinating diseases. Multiple sclerosis, the most common demyelinating disease, generally occurs in adults substantially after the active myelination period in CNS development has ended. A deletion-transfection analysis has confirmed the importance of regulatory sequences located within the first intron that are essential for regulating P/p gone expression. One of these elements, the so-called ASE, for antisilencer/enhancer, appears to cause a dramatic increase in P/p gene expression during (and after) the myelination period of CNS development. We believe that multiple factors assemble on the ASE to form a stereospecific nucleoprotein structure termed an """"""""enhanceosome."""""""" To understand how the ASE mediates P/p gone activation, the following specific aims have been proposed: 1) Characterize further the ASE, a positive cis-acting regulatory element located in intron 1 DNA, which promotes high levels of P/p gene expression in oligodendrocytes; 2) Identify the nuclear factors, which form a transcriptional regulatory complex on the ASE; 3) Elucidate the mechanism whereby the ASE nucleoprotein complex activates P/p gone expression in oligodendrocytes. ? ?
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