Structural features of the rat GFAP gene and identification of a novel alternative transcript

The glial fibrillary acidic protein (GFAP) is expressed in a cell-specific manner and represents the major subunit of intermediate filaments of astrog lial cells. The knowledge of the gene structure is an important step for fu rther understanding the mechanisms of cell-specific expression. In the pres ent study, we report the complete sequence of the rat GFAP gene and provide evidence for the existence, in the rat brain, of a novel alternative trans cript. Since three different transcripts, indicated as GFAP alpha, beta, an d gamma, have been previously reported (Feinstein et al, [1992] J. Neurosci . Res. 32:1-14; Zelenika et al. [1995] Mol. Brain Res. 30:251-258), we call ed this novel mRNA isoform GFAP delta. It is generated by the alternative s plicing of a novel exon located in the classic seventh intron. This alterna tive exon (called VII+) contains a 101-bp coding sequence in frame with exo n VII and interrupted by a stop codon TAA at position +5451. Therefore, the novel GFAP delta transcript encodes for an hypothetical GFAP where the for ty-two carboxyterminal amino acids encoded by exon VIII and IX are replaced by thirty-three amino acids encoded by exon VII+. Northern blot analysis w ith a specific probe for exon VII+ revealed a 4.2-kb mRNA, expressed in sev eral brain areas, but absent in extracerebral tissues (lung, heart, kidney, liver, spleen). The previously discovered GFAP isoforms (alpha, beta, and gamma) produce hypothetical translation products differing in the aminoterm inal Head domain. The present data suggest, for the first time, the possibl e existence of GFAP isoforms differing in the carboxy-terminal Tail domain. J. Neurosci. Res. 56:219-228, 1999. (C) 1999 Wiley-Liss, Inc.