Splice Variant of Mouse Stam2 MRNA in Nervous and Muscle Tissue Contains Additional Exon with Stop Codon Within Region Coding for VHS Domain

Aim: To analyze the alternatively spliced variant of Stam2 mRNA and determine its distribution in mouse tissues.

Methods: We identified a novel alternatively spliced exon by cloning and sequencing of Stam2 cDNA obtained from tissue samples of 3-5 months old male C57Bl/6NCrl mice. The sequence of the alternatively spliced exon was analyzed by bioinformatic tools. The tissue distribution of different Stam2 mRNA variants was determined by reverse transcription-polymerase chain reaction, and the consequences of the alternative splicing at the protein level were analyzed by western blot with the polyclonal anti-STAM2 antibody.

Results: The novel alternatively spliced exon 1A of mouse Stam2 gene was inserted within Stam2 coding region and it contained a stop codon. The exon did not bear similarities to any other cDNA or protein sequence in the mouse, rat, or human databases. Both mRNA variants, with and without exon 1A, were present in the cortex, hippocampus, olfactory bulb, medulla oblongata, spinal cord, cerebellum, and the skeletal and heart muscle, while the other analyzed organs contained only the variant without the additional exon. The mRNA with the included exon did not give rise to a protein form detectable by western blotting with the polyclonal anti-STAM2 antibody.

Conclusion: The alternatively spliced exon 1A was included in mRNA splice variant present in the nervous and muscle tissues. The alternative splicing event did not have major impact on STAM2 production and functionality. It seems that exon 1A is an evolutionary new exon created by exonization of an intronic sequence.