Identification of rat Gas7 isoforms differentially expressed in brain and regulated following kainate-induced neuronal injury.

The growth arrest-specific gene 7 (Gas7) is expressed primarily in the brain and is necessary for the formation of neurite in cultured cerebellar preneurons. The endogenous rat Gas7 (rGas7) is transiently elevated before nerve growth factor-promoted neurite outgrowths emerge in cultured PC12 cells. We report three Gas7 isoforms (a, b, and c) in rat tissues. Peptide microsequencing identified two Gas7 forms, rGas7-a (38 kDa) and rGas7-b (47 kDa). rGas7-c can be predicted from a transcription variant by alternative splicing. Although two open reading frames were predicted, a cloned rGas7 cDNA encoded mostly rGas7-a in mammalian cells. The overexpression of the rGas7 cDNA in PC12 cells sufficed to promote small lamellipodia- and filopodia-like cell processes that resemble the initial stages of neurite formation. Three rGas7 isoforms were differentially expressed in all of the brain subregions. Only rGas7-a was detected in rat cerebellum, as in mouse cerebellum. Kainate injury did not affect the level of rGas7-b, but the level of isoform c was substantially suppressed in the hippocampus. Immunohistochemistry reveals that Gas7 was expressed primarily in the pyramidal neurons of the hippocampus and was quickly attenuated before recovery in the CA3 area after kainate was administered. These results suggest that differential expression and unique regulation of Gas7 isoforms in brain subregions may be important in specialized brain functions. Conservation of Gas7 isoforms by alternative splicing in mammals is also considered.