Status of the Janus Kinase-Signal Transducer and Activator of Transcription (JAK-STAT) pathway in liver and skin of the freeze tolerant wood frog

The wood frog (Rana sylvatica) has adapted full-body freezing and thawing as a means of sub-zero winter survival and early-breeding in ephemeral pools. One such protective process implicated recently in freeze-thaw tolerance is that of anti-apoptotic signaling, which has been proposed to play a cytoprotective role by modulating stress -induced death signals. This study employed the use of immunoblotting to examine response of a potent cell cycle and apoptosis regulator, known as the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway, to freezing and thawing in the liver and skin of the wood frog. This pathway demonstrably exhibits factor-and tissue-specific changes between non-frozen, 24 h-frozen, and 8 h-thawed conditions. There were few changes in JAK-STAT proteins in frozen frogs, but protective changes were observed upon thaw: Elevated levels of pJAK3 and nuclear localization of pSTAT3 and pSTAT5 suggested an increase in anti-apoptotic signaling after thaw. By contrast, both STAT1 and STAT3 signaling appeared to increase in frozen skin, sug-gesting frogs use homeostatic regulation of apoptotic-and anti-apoptotic signals, in an antagonistic and compensatory manner. As such, these findings support that JAK-STAT pathway signaling modulation is a plausible adaptation that contributes to fast and reversible manipulation of anti-apoptotic signals, thus assisting in freeze survival of the wood frog.