Alternative splicing of the tuberous sclerosis 2 (TSC2) gene in human and mouse tissues

The recently isolated gene for tuberous sclerosis 2 (TSC2) encodes a 5.5-kb transcript that is widely expressed. The TSC2 gene product, named tuberin, is a 1784-amino-acid protein that shows a small stretch of homology to the GTPase activating protein rap1GAP. We have detected a novel variant of the TSC2 mRNA lacking 129 nucleotides, predicting an in-frame deletion of 43 amino acids spanning codons 946-988 of tuberin. This 129-bp deletion precisely corresponds to exon 25 of the TSC2 gene suggesting that alternative splicing leads to production of two forms of transcripts designated isoforms 1 and 2. Further molecular analysis revealed a third isoform exhibiting a deletion of 44 amino acids spanning codons 946-989 of tuberin. Amino acid 989 is a Ser residue encoded by the first codon of exon 26. The two isoforms also exist in newborn and adult mouse tissues, reinforcing the potential functional importance of these alternatively spliced products. These alternative isoforms should have implications for efforts aimed at identifying mutations in TSC patients. The distinct polypeptides encoded by the TSC2 gene may have different targets as well as functions involved in the regulation of cell growth.