Hibernation-specific alternative splicing of the mRNA encoding cold-inducible RNA-binding protein in the hearts of hamsters.

The hearts of hibernating animals are capable of maintaining constant beating despite a decrease in body temperature to less than 10 °C during hibernation, suggesting that the hearts of hibernators are highly tolerant to a cold temperature. In the present study, we examined the expression pattern of cold-inducible RNA-binding protein (CIRP) in the hearts of hibernating hamsters, since CIRP plays important roles in protection of various types of cells against harmful effects of cold temperature. RT-PCR analysis revealed that CIRP mRNA is constitutively expressed in the heart of a non-hibernating euthermic hamster with several different forms probably due to alternative splicing. The short product contained the complete open reading frame for full-length CIRP. On the other hand, the long product had inserted sequences containing a stop codon, suggesting production of a C-terminal deletion isoform of CIRP. In contrast to non-hibernating hamsters, only the short product was amplified in hibernating animals. Induction of artificial hypothermia in non-hibernating hamsters did not completely mimic the splicing patterns observed in hibernating animals, although a partial shift from long form mRNA to short form was observed. Our results indicate that CIRP expression in the hamster heart is regulated at the level of alternative splicing, which would permit a rapid increment of functional CIRP when entering hibernation.