Mild hypothermia promotes the viability of in vitro-produced bovine blastocysts and their transcriptional expression of the cold-inducible transcription factor Rbm3 during in vitro culture

In this study, we evaluated the effects of holding in vitro-produced bovine blastocysts under mild hypothermia (33 degrees C or 35 degrees C), by examining viability and hatching rates of day 7 blastocysts (day 0: in vitro fertilization) cultured for 6 days and transcriptional expression of cold-inducible transcription factors Cirp and Rbm3, implicated in mild hypothermia-induced cellular protection against various types of stress. In the normothermic control (38.5 degrees C), viability of the embryos decreased rapidly after day 10, and most samples were degenerated on day 13. However, mild hypothermia, particularly at 33 degrees C, resulted in maintenance of high embryonic survival rates until day 13 (77.1% on day 13) and significant increases in transcriptional expression of Rbm3 in day 11 embryos compared with those at 38.5 degrees C. Thus, our results suggested that upregulation of Rbm3 may occur in response to mild hypothermia in many bovine embryos, providing insights into the effects of mild hypothermia on embryo quality.