Regional expression of myelin protein genes in the developing mouse brain: In situ hybridization studies

Abstract

Expression of mRNAs for the two major myelin proteins, myelin basic protein (MBP) and proteolipid protein (PLP), was examined in a number of regions of the developing mouse brain using in situ hybridization. In general, MBP and PLP mRNAs were observed to be coexpressed during ontogeny, prior to the histological appearance of myelin. Expression of both mRNAs was detected as early as 6 hours postpartum in the medulla oblongata and, with development, expression of these mRNAs progressed in a caudal to rostral direction. Peak expression occurred at approximately postnatal day 20 in most regions examined, regardless of time of onset of expression. As myelination proceeded, two different labeling patterns were observed with the PLP and MBP 35S-labeled cDNA probes. In the earliest stages of myelinogenesis MBP mRNA labeling was restricted to oligodendrocyte cell bodies, but shortly after the gene began to be expressed the labeling became more diffuse. In contrast, PLP mRNA labeling remained over or surrounding oligodendrocyte cell bodies at all stages of myelinogenesis. These two distinctly different patterns of labeling are consistent with alternative intracellular trafficking of MBP and PLP mRNAs, in which PLP mRNAs remain associated with ribosomes within the cell soma and MBP mRNAs move from the cell soma to the oligodendrocyte processes at a specific stage early in myelinogenesis. However, there appeared to be a clear time lag between the onset of MBP mRNA expression and the movement of ribosomes carrying MBP mRNAs into the oligodendrocyte processes. Additionally, the in situ hybridization studies revealed a population of unidentified cells residing in cortical molecular layers that express PLP mRNA in the absence of MBP mRNA.

Connexin29 and connexin32 at oligodendrocyte and astrocyte gap junctions and in myelin of the mouse central nervous system

“…Examination of Cx29 levels during development indicated a temporal and spatial expression pattern consistent with the known onset time and caudal-to-rostral progression of myelination along the neuraxis (Verity and Campagnoni, 1988). Unlike transiently elevated levels of several connexins during brain development (Prime et al, 2000), Cx29 protein continuously increased to maximum levels in the adult CNS.…”

Connexin47, connexin29 and connexin32 co-expression in oligodendrocytes and cx47 association with zonula occludens-1 (zo-1) in mouse brain

“…Analyses of oligodendrocyte Cxs by subcellular fractionation of whole brain confirmed previous reports of an enrichment of Cx29 and Cx32 in the myelin fraction Nagy et al, 2003a) and supported our anatomical observations by showing relatively low levels of Cx47 in myelin, as compared with other fractions. Further evidence for the relatively low levels of Cx47 association with myelin compared with oligodendrocyte somata was indirectly provided by the progressively increasing density of myelin in the rostro-caudal direction of the neuraxis (Verity and Campagnoni, 1988), which was reflected by a similar rostro-caudal increasing gradient in Cx29 levels (Nagy et al, 2003a), but contrasted with the relatively uniform levels of Cx47 in all brain regions examined.…”

A model of the development of the brain as a construct of the thyroid system.

“…For example, myelination of the spinal nerve roots begins around gestation month 5, whereas myelination of the auditory cortex does not begin until gestation week 9. Likewise, myelinogenesis in the rat brain occurs in a regional pattern (87). Myelination of the vestibulo-cochlear nerve (cranial nerve VIII) is evident by PND2 (56), whereas onset of myelin protein gene expression in the cerebellum and cerebral cortex occurs on PND10 and PND20, respectively (57).…”