Abstracts

Abstract

Previous studies from our lab have shown that a cDNA clone encoding GFAP isolated from cultured Schwann cells (GFAP-β) differs from themRNA in the CNS (GFAP-α) by the presence of an extended 5′ untranslated region (UTR). Primer extension analysis of Schwann cell mRNA places the major transcriptional start site 157 bases upstream of the CNS cap site. Polymerase chain reaction assays (PCR) suggest that the longer 5′ UTR is contiguous with the genomic sequence. A PCR assay has been developed to distinguish the 2 GFAP mRNAs and allow rapid quantitation of their levels. GFAP-β mRNA is expressed in various Schwann cell lines to different extents, all of which express exclusively the PNS-GFAP. In RT4-D6 cells, GFAP-β constitutes at least 80–85% of the total GFAP mRNA. As found with astrocytes treatment of these cells with 1 mM dbcAMP for 24 hr led to an increase in GFAP-β levels. GFAP-β mRNA also constitutes the predominant GFAP mRNA in mouse retina, suggesting that all examples of peripheral type GFAP may be a consequence of the longer 5′ UTR. GFAP-β is expressed at low levels in cultured rat cortical astrocytes and is slightly increased (2-fold) by treatment of the cells with 1 mM dbcAMP. In contrast, treatment with IFN-γ, an activator of astrocytc gene expression, led to a dramatic increase in GFAP-p while at the same time causing a decrease in overall GFAP mRNA levels such that GFAP-β represented over 90% of total GFAP mRNA. In rat cortex, GFAP-β mRNA expression paralleled that of total GFAP mRNA levels, reaching maximum levels between postnatal days 10 and 15. Relative GFAP-β levels in cerebellum were higher than in cortex. These results indicate that the regulation of GFAP-β mRNA expression can differ from that of GFAP-α mRNA and, hence, increases in this mRNA may be diagnostic of developmental or pathological conditions from those which influence total GFAP levels.