Developmental expression of glial-specific mRNAs in primary cultures of rat brain visualized by in situ hybridization

The localization of mRNAs which encode the glial-specific marker proteins, glial fibrillary acidic protein (GFAP), glycerol phosphate dehydrogenase (GPDH, EC 1.1.1.8), and myelin basic protein (MBP), was mapped by in situ hybridization in primary cultures of 1-2-day-old rat brain in serum-supplemented medium. Developmental changes of these expressed mRNAs were examined after various times in culture ranging from 8 to 50 days and were correlated with the histological, morphological, and positional characteristics of the cells. By day 8, the culture stratified into a population of flat polygonal astrocytes covered by another population of phase-dark process-bearing cells. When counterstained with May-Grunwald histological stain, astrocytes appeared pale blue, whereas two subpopulations of phase-dark cells stained differentially; one was dark blue while the other was red and smaller. GFAP-specific sequences were abundant at day 8, increased in the astrocyte bedlayer as the culture became confluent, and plateaued at approximately day 16. A minor proportion of blue phase-dark cells contained GFAP mRNA although at a lower abundance. In contrast, GPDH mRNA positive blue phase-dark cells were seen scattered throughout the upper layer of the culture and also around the perimeter of large clumps of red phase-dark cells. These cells were infrequent at day 8 but increased in number at later time points. The expression of MBP mRNA differed from GPDH in that it was more abundant at early time points, plateaued between day 20 and day 24, and was predominantly localized in red phase-dark cells.(ABSTRACT TRUNCATED AT 250 WORDS)