Alternative mRNA Splicing from the Glial Fibrillary Acidic Protein (GFAP) Gene Generates Isoforms with Distinct Subcellular mRNA Localization Patterns in Astrocytes

The intermediate filament network of astrocytes includes Glial fibrillary acidic protein (Gfap) as a major component. Gfap mRNA is alternatively spliced resulting in generation of different protein isoforms where Gfap alpha is the most predominant isoform. The Gfap delta isoform is expressed in proliferating neurogenic astrocytes of the developing human brain and in the adult human and mouse brain. Here we provide a characterization of mouse Gfap delta mRNA and Gfap delta protein. RT-qPCR analysis showed that Gfap delta mRNA and Gfap alpha mRNA expression is coordinately increased in the post-natal period. Immunohistochemical staining of developing mouse brain samples showed that Gfap delta is expressed in the sub-ventricular zones in accordance with the described localization in the developing and adult human brain. Immunofluorescence analysis verified incorporation of Gfap delta into the Gfap intermediate filament network and overlap in Gfap delta and Gfap alpha subcellular localization. Subcellular mRNA localization studies identified different localization patterns of Gfap delta and Gfap alpha mRNA in mouse primary astrocytes. A larger fraction of Gfap alpha mRNA showed mRNA localization to astrocyte protrusions compared to Gfap delta mRNA. The differential mRNA localization patterns were dependent on the different 3'-exon sequences included in Gfap delta and Gfap alpha mRNA. The presented results show that alternative Gfap mRNA splicing results in isoform-specific mRNA localization patterns with resulting different local mRNA concentration ratios which have potential to participate in subcellular region-specific intermediate filament dynamics during brain development, maintenance and in disease.