The cellular and subcellular distributions of mRNAs encoding three myelin-specific proteins-myelin basic protein (MBP), proteolipid protein (PLP), and Po proteinwere studied in tissue sections of developing rat nervous systems by in situ hybridization. The developmental appearance of these mRNAs closely paralleled the appearance of the proteins they encode as determined by immunocytochemistry. mRNA encoding the extrinsic membrane protein, MBP, was concentrated around oligodendrocyte and Schwann cell nuclei during initial stages of myelination; as myelination proceeded, MBP mRNA became distributed diffusely over myelinated fibers. In contrast, mRNAs encoding the intrinsic membrane proteins, PLP and Po, remained concentrated around oligodendrocyte (PLP) and Schwann cell (Po) nuclei at all stages of myelination. These results establish that myelinating cells spatially segregate certain myelin-specific mRNAs. The presence of MBP mRNA within the cytoplasmic domains of myelin internodes indicates that protein sorting during myelination involves transportation of mRNA to specific subcellular sites.Myelin, a multilamellar compact membrane, surrounds many axons in the central and peripheral nervous systems (CNS and PNS). CNS myelin is formed by oligodendrocytes, which individually have the potential to form 30-40 different myelin internodes by extending long slender cytoplasmic processes that ensheath and spirally wrap around axons to form compact myelin. In the PNS, Schwann cells form single myelin internodes. The protein composition of CNS and PNS myelin is well characterized (1). Ultrastructural studies have shown that CNS and PNS myelination occurs in a systematic and predictable manner (2, 3), suggesting that myelin-forming cells utilize very efficient mechanisms for synthesis, transport, and integration ofmyelin components to accomplish the massive expansion of membrane.Formation of myelin represents a terminal phenotypic expression of oligodendrocytes and Schwann cells that must involve the expression of a myelin-specific genetic program. DNAs complementary (cDNA) to the mRNAs that encode several myelin proteins have been cloned recently (4-10). Using these clones, the time courses for expression of myelin-specific mRNAs have been analyzed during development (4-10). The present study focuses on the cellular distribution of three myelin-specific mRNAs. Using in situ hybridization, we determined when these mRNAs could first be detected during early stages of myelination and asked whether spatial segregation of certain mRNAs might occur. (Kodak) melted at 43°C and diluted 1:1 with 0.6 M ammonium acetate. After development of the emulsion, the sections were stained with hematoxylin, dehydrated, and overlaid with coverslips. Sections were photographed with a Zeiss photomicroscope using bright-field and dark-field optics.The cDNA clones used have been well characterized and described elsewhere: proteolipid protein (PLP) (6), MBP (4), and Po (8). The specificity of cDNA hybridization was demonstrated by pretrea...

JC virus UCV) causes the chronic human demyelinating disease progressive multifocal leukoencephalopathy. Because of host range restrictions, experimental models of JCV-induced demyelination have not been available. The restricted tropism of JCV infectivity has recently been overcome by the production of transgenic mice that contain the early region of JCV in all cells. This portion of the DNA encodes JCV T-antigens. These mice display a dysmyelinating phenotype, the severity of which is related to the level of JCV early region expression in brain. With the use of immunocytochemistry and in situ hybridization, we characterized morphologically myelin-specific and JCV gene expression in a severely affected strain of these mice. Our results suggest that expression of JCV T-antigens occurs predominantly in oligodendrocytes and is the primary cause of dysmyelination. Affected oligodendrocytes do not myelinate axons properly. However, they express myelin-specific genes and display some of the morphological phenotypes of early stages of myelination. A decreased ratio between levels of transcriptional and translational products of genes encoding the major structural proteins of central nervous system myelin was apparent. These results suggest that JCV T-antigens arrest the maturation of oligodendrocytes and inhibit the production of myelin. These results also demonstrate that JCV transgenic mice are a good model for investigating mechanisms of JCV-induced demyelinating lesions in progressive multifocal leukoencephalopathy. Trapp BD, Small JA, Pulley M, Khoury G, Scangos GA. Dysmyelination in transgenic mice containing JC virus early region. Ann Neurol 1988;23:38-48 JC virus UCV) is a human papovavirus that causes the chronic central nervous system (CNS) demyelinating disease progressive multifocal leukoencephalopathy (PML). Although this virus is widespread [l, 21, PML is a rare opportunistic disease that occurs predominantly in immunocompromised persons 131. For example, the incidence of PML is relatively high in patients with acquired immunodeficiency syndrome 141, sarcoidosis, or renal transplants 131. In demyelinating lesions from PML brain, JC virions are present within abnormal oligodendrocytes 151; demyelination is assumed to result from selective lytic infection of these myelin-producing cells. In addition, astrocytes in PML brains can have bizarre morphological characteristics that include some features found in transformed cells [S}. Virions are only rarely observed in electron micrographs of these astrocytes. Experimental models of JCV-induced demyelination have not been available. When inoculated into newborn hamsters, JCV causes a variety of tumors [6-8} derived primarily from neural tissue. JCV is the only human virus known to cause tumors in primates (owl and squirrel monkeys) in which Grade IV astrocytomas or glioblastomas develop 18 to 24 months after intracranial injection 191. JCV has not been shown to induce any detectable abnormality when injected into mice 1101.To produce an experimental model for JC...

JC virus (JCV) causes the chronic human demyelinating disease progressive multifocal leukoencephalopathy. Because of host range restrictions, experimental models of JCV-induced demyelination have not been available. The restricted tropism of JCV infectivity has recently been overcome by the production of transgenic mice that contain the early region of JCV in all cells. This portion of the DNA encodes JCV T-antigens. These mice display a dysmyelinating phenotype, the severity of which is related to the level of JCV early region expression in brain. With the use of immunocytochemistry and in situ hybridization, we characterized morphologically myelin-specific and JCV gene expression in a severely affected strain of these mice. Our results suggest that expression of JCV T-antigens occurs predominantly in oligodendrocytes and is the primary cause of dysmyelination. Affected oligodendrocytes do not myelinate axons properly. However, they express myelin-specific genes and display some of the morphological phenotypes of early stages of myelination. A decreased ratio between levels of transcriptional and translational products of genes encoding the major structural proteins of central nervous system myelin was apparent. These results suggest that JCV T-antigens arrest the maturation of oligodendrocytes and inhibit the production of myelin. These results also demonstrate that JCV transgenic mice are a good model for investigating mechanisms of JCV-induced demyelinating lesions in progressive multifocal leukoencephalopathy.