Alternative splicing of the 5'-sequences of the mouse EAAT2 glutamate transporter and expression in a transgenic model for amyotrophic lateral sclerosis.

Glutamate-mediated neurotoxicity and a reduced expression of the excitatory amino acid transporter 2 (EAAT2) have been described in the pathogenesis of several acute and chronic neurological conditions. EAAT2 is the major carrier of glutamate in the mammalian brain. However, the principles of EAAT2 expression regulation are not fully understood. For the human brain, extensive alternative splicing of the EAAT2 RNA has been shown. To delineate the complex RNA regulation of EAAT2 we investigated whether the murine species is a suitable model for the study of EAAT2 splicing events. We identified five splice variants (mEAAT2/5UT1-5) encoding different 5'-untranslated sequences and two distinct N-termini of the putative EAAT2 polypeptide. In the murine CNS we found a region-specific expression pattern of the novel 5'-variants of EAAT2 as shown by in situ hybridization, dot blotting and competitive reverse transcription polymerase chain reaction. Furthermore, we performed an expression analysis of the EAAT2 splice variants in the spinal cord of a transgenic model (SOD1G93A) of amyotrophic lateral sclerosis, a motor neurone disease for which altered splicing of EAAT2 has been discussed. We found an increased expression of mEAAT2/5UT4 and a reduction of mEAAT2/5UT5 in the early course of the disease. We conclude that alternative splicing of 5'-sequences may contribute to the regional expression of the EAAT2 RNA and was altered in the pre-symptomatic stage of the SOD1G93A-mouse model for amyotrophic lateral sclerosis.