GFAPβ mRNA Expression in the Normal Rat Brain and after Neuronal Injury

GFAPβ mRNA is an alternative transcript of the glial fibrillary acidic protein (GFAP) gene, whose transcriptional start site is located 169 nucleotides upstream to the classical GFAPα mRNA. By an RT-PCR method with primers on separate exons, we were able to confirm the presence of GFAP transcripts with a longer 5′ untraslated region in all the examined areas of rat brain and in primary cultures of astroglial cells. Northern blot analysis, using an oligoprobe specific for the 5′ region of GFAPβ, revealed a single hybridization band of 2.9 kb in all the brain regions examined and in primary cultures of astroglial cells. The availability of the quantitative Northern blot assay allowed further studies on the regulation of GFAPβ expression in vivo. Since it is well-known that neuronal brain injury is one of the most powerful inducers of GFAP, we examined the expression of GFAPα and β after a neurotoxic lesion in the rat hippocampus. Results obtained show a parallel increase in both GFAP transcripts with an identical time-course, suggesting that regulatory regions of the gene influence in similar way the rate of transcription at the two different start sites (α and β) or that a similar post-transcriptional mechanism is involved in regulating both mRNA isoforms.