We analyzed the location and abundance of transcripts for the 4 CNS myelin protein genes, myelin basic protein (MBP), proteolipid protein (PLP), myelin-associated glycoprotein (MAG), and 2',3'-cyclic nucleotide phosphohydrolase (CNP), in the mouse cervical spinal cord from the time of rapid myelination until adulthood (8-45 d). In the white matter, maximal levels of transcripts were found for each of the myelin genes at the peak of myelination (8 d). Total MBP and PLP mRNAs stayed high until 20 d and showed a minor decrease thereafter. In contrast, MAG and the MBP exon 2 containing transcripts (coding for the 21.5 and 17 kDa MBP isoforms) decreased sharply between 8 and 20 d, suggesting that high levels of these transcripts are needed primarily during the initiation of myelination. CNP transcripts were less abundant, maintained high expression until 20 d, and then decreased sharply. PLP, MAG, and CNP transcripts were clustered in the oligodendrocyte cell body, while MBP mRNAs were scattered throughout the cell body and processes. In contrast to the white matter, all these myelin specific transcripts in the gray matter showed a marked increase from 8 to 20 d, as did the number of oligodendrocytes identified by CNP immunostaining. MAG transcripts were found in white matter and in satellite and other oligodendrocytes of the gray matter but not in neurons identified by their expression of neurofilament transcripts. The results of our quantitative in situ hybridization study are in good agreement with those of previous molecular studies and provide new information on the cellular and topographic distribution of myelin-specific mRNAs during myelination.

C57BI/6N mice develop a CNS demyelinating disease when inoculated intracranially at 4 weeks of age with the A59 strain of mouse hepatitis virus (MHV-A59). In order to explore the virus-host interactions, the histological features of the demyelinating disease were correlated with the spatial and temporal distribution of viral transcripts and the expression of oligodendrocyte-specific genes (myelin basic protein, proteolipid protein, myelin-associated glycoprotein, and 2',3' cyclic nucleotide 3'-phosphohydrolase) in the spinal cord of diseased mice. Three distinct phases in the disease were identified. In the first phase, 1 week postinfection (1 WPI), virus replication was widespread in both gray and white matter but was preferentially occurring in glial cells. In the ventral and dorsal root zones where viral transcripts were most abundant, all myelin gene transcripts were decreased before demyelination was seen. During the second phase of the disease (2-3 WPI), viral transcripts decreased in abundance and became restricted to the white matter. Numerous demyelinating lesions were observed and were characterized by inflammatory cells, paucity of oligodendrocytes, and a profound decrease of all myelin gene transcripts. In the third phase of the disease (4-6 WPI) no viral transcripts were detected, and remyelination began. In the lesions and the tissue surrounding them, transcripts of all myelin genes increased to levels above normal. The increased expression of myelin gene transcripts occurred in a synchronized manner and with a cellular distribution reminiscent of that seen in developmental myelination. These molecular events correlated with efficient remyelination and clinical recovery in this murine demyelinating disease.

In the central nervous system of AIDS patients, human immunodeficiency virus (HIV) infects primarily microglia, a cell type of bone marrow origin. Moreover, microglial cells isolated from adult human brain support the replication of macrophage-adapted strains of HIV type 1 (HIV-1) (B. A

1. In order to characterize some of the molecular events leading to repair of myelin in the adult central nervous system (CNS), we examined the expression of transcripts for myelin basic protein (MBP) during remyelination in the mouse. C57B1/6 mice develop a demyelinating disease when glial cells are selectively infected by the A59 strain of mouse coronavirus. The virus is spontaneously cleared from the mice by 4 weeks postinfection (WPI), a time when remyelination is starting. 2. At 3 WPI total MBP transcripts are decreased by 75% in demyelinating lesions compared to control white matter. Using RNase protection assays and in situ hybridization with probes for particular MBP exons, we detected an increase in MBP transcripts containing exon 2 information, coincident with the earliest histological signs of remyelination. 3. The expression of MBP transcripts containing exon 2 information was first seen clustered in the perinuclear cytoplasm of oligodendrocytes scattered within the lesions. This is reminiscent of the increased levels and perinuclear clustering of MBP transcripts containing exon 2 seen during early developmental myelination. The peak abundance of exon 2-containing transcripts in the lesions was 13-fold that seen in control white matter. At later stages of remyelination, additional forms of MBP transcripts (without exon 2) increased and their distribution was more diffuse. 4. Thus, during remyelination, preforms of MBP transcripts, which are normally present at low levels in the adult CNS, are abundantly expressed and regulated in a manner similar to that observed in developmental myelination.