Identification and expression analysis of alternative splice variants of the rat Hax-1 gene

Hax-1 protein, which has been studied in mice and humans, shows a potent anti-apoptotic activity and is involved in regulation of cell motility. Cloning of the rat Hax-1 cDNA has revealed seven alternative transcripts, which differ mostly in their 5' region. Alternative splicing concerns exon 1, skipped in 5 transcripts, intron 1 which is partially retained in these transcripts, exon 2, which can be partially skipped, and intron 2, retained in one variant. The existence of different splicing variants was confirmed by exon-junction-specific RT-PCR and RNase protection assay. Analysis of expression indicates that overall Hax-1 mRNA level is relatively low in most tissues and very high in testes, and that the expression pattern of the variants is similar in different tissues. Presence of different transcripts implies the existence of several protein isoforms, with three putative start codons. The existence of at least three protein isoforms was confirmed by Western blot. Interestingly, high mRNA level in testes does not translate into high protein level, suggesting the existence of tissue-specific translational regulation or regulated protein degradation.