Multiple Regulatory Elements Control Transcription of the Peripheral Myelin Protein Zero Gene

Abstract

The gene encoding protein zero (P 0 ), the most abundant protein of peripheral nervous system myelin, is expressed uniquely in Schwann cells. Previous studies have demonstrated that much of the cell type specificity of this expression is due to transcriptional control elements in the 1.1-kilobase pair 5-regulatory region of the gene. We have now analyzed this region and have identified a set of functional elements in the 500 base pairs proximal to the transcription start site. DNA sequence conservation within the 5 regions of the human, mouse, and rat P 0 genes correlates closely with the results of promoter deletion analysis of the 1.1-kilobase pair region assayed in Schwann cell cultures and reveals a potent proximal region from position ؊350 to ؉45. Sites of protein/DNA interaction within the proximal 500 base pairs of the promoter were identified by footprinting assays. Functional transcriptional elements were identified within the protected regions in the proximal promoter by mutation and transient transfection analysis in P 0 -expressing cell lines. The core (or basal) P 0 promoter is identified as two regulatory elements, a G/Crich element that binds nuclear factor Sp1 and a CAAT box that binds NF-Y. These core elements are essential for the transcription observed from the transfected promoter in cultured Schwann cells.The myelin sheath is a specialized membranous organelle of the vertebrate nervous system. Elaborated by oligodendrocytes in the central nervous system and by Schwann cells in the peripheral nervous system (PNS), 1 this organelle consists of a large sheet of plasma membrane that is repeatedly wrapped and very tightly compacted around axons (1). Myelin is essential for the rapid conduction of action potentials in vertebrates, and human diseases that compromise the integrity of the sheath (e.g. peripheral neuropathies in the PNS and multiple sclerosis in the central nervous system) are generally debilitating (2). The elaboration of myelin requires a substantial biosynthetic up-regulation of plasma membrane lipids and proteins, several of which are unique to the myelin sheath (3). In the PNS, the most abundant of these is protein zero (P 0 ), a 31-kilodalton, immunoglobulin-related, transmembrane glycoprotein that accounts for greater than 50% of the protein in mammalian PNS myelin (4). The mRNA encoding this protein is estimated to account for nearly 8% of the poly(A) RNA in actively myelinating Schwann cells (5).A variety of studies have demonstrated that P 0 is essential for peripheral nerve development and function. Mice in which the P 0 gene has been deleted exhibit a severe peripheral neuropathy that includes hypomyelination, loss of motor control, tremors, and grossly abnormal myelin sheaths (6, 7). Furthermore, mutations in the P 0 gene account for a variety of inherited human peripheral neuropathies, including Charcot-MarieTooth disease type 1B, Dejerine-Sottas syndrome, and congenital hypomyelination (8 -12).High level P 0 expression is a distinctive feature of terminal differentiatio...

Activation of Myelin Genes during Transdifferentiation from Melanoma to Glial Cell Phenotype

“…SCIP, like Pax3, is an inhibitor that is down-regulated before SC activate myelin gene expression (5). For Sp1, a binding site at Ϫ55/Ϫ50 in the rat Po promoter was reported as required for the basal Po promoter activity (8), but this site is not in the region that we find essential for the response to IL6RIL6. We, therefore, searched in the Ϫ300/Ϫ137 region of the Po promoter for sequence elements that are positively involved in the response to IL6RIL6 and to Sox10.…”

“…rat Po promoter sequence mediating tissue-specific expression of Po contains a number of binding sites for known transcription factors (8,16), some of which are indicated in Fig. 5A.…”

N-Acetylaspartate in the CNS: From neurodiagnostics to neurobiology

“…Many of the proteins expressed by oligodendrocytes and Schwann cells are distinct. For example, the major myelin-associated proteins in the CNS are PLP, its alternative splice variant DM20 and myelin basic protein (Garbern, 2005), whereas the predominant myelin-associated proteins in the PNS are protein zero (P O ), peripheral myelin protein 22kD (PMP22) and myelin basic protein (Brown and Lemke, 1997;Jiang et al, 2000).…”

Upstream Elements Involved in Vivo in Activation of the Brain-specific Rat Aldolase C Gene

“…Region-A functional synergy between distal and proximal regulatory elements has been reported to be involved in the transcriptional control of numerous genes (36,37), including neural genes (3,9,38,39), and is well illustrated by the case of the rat aldolase C gene. Indeed, high level expression of the aldolase C/CAT constructs in the brains of transgenic mice required cooperation between a 0.6-kb fragment located immediately upstream of the tissuespecific but weak 115-bp proximal promoter and a far upstream 3.8-kb region (Fig.…”