Brain-specific splicing of alpha-actinin 1 (ACTN1) mRNA

Two isoforms of alpha-actinin 1 (ACTN1) known to be generated by tissue-specific alternative splicing of mutually exclusive exons have been described. Muscle cells express ACTN1 containing the smooth muscle exon (SM), while other (non-muscle) cells contain the non-muscle exon (NM). In this report, we describe the characterization of a novel ACTN1 isoform in adult rat brain in which both exons (NM + SM) are combined in the same transcript to give a brain-specific sequence domain (BS). Reverse transcriptase polymerase chain reaction (RT-PCR) demonstrated that expression of the BS exon was restricted to the brain. During development, weak expression of the BS exon was observed at early postnatal stages whereas in adult brain, it represented the predominant isoform of ACTN1. In situ hybridization analysis revealed that BS expression was highest in neurons of the hippocampus, cortex, and caudate putamen while the cerebellum and other subcortical structures showed only weak labeling.