Frozen Alive: Gene Secrets of Freeze Tolerant Animals Show New Directions for Cryomedicine
Although alien to the physiology of man, natural freeze tolerance is key to winter survival for various amphibians and reptiles as well as many invertebrate species. These animals survive for weeks with as much as ~65% of total body water frozen as extracellular ice. By unraveling the molecular secrets of natural freezing survival of frogs and turtles, we advance our understanding of both cryoinjury and cryopreservation and identify molecular targets for the development of organ cryopreservation technology. Rapidly advancing genomic and proteomic technologies are producing key advances in our understanding of how cells and organisms survive freezing. Our previous focus on cell protection (e.g. packing cells with cryoprotectants) is giving way to an understanding of the full range of genetic adjustments that support natural freezing survival including freeze responsive genes involved in ischemia protection, antioxidant defenses, cell volume regulation, membrane transporters, signal transduction cascades (protein kinases and phosphatases), and metabolic arrest mechanisms. My lab has successfully utilized methods including cDNA library screening, the use of DNA arrays and transcription factor protocols to identify a wide range of gene targets that show strong up-regulation during natural freezing exposure, many of them common across phylogenetic lines. Screening of cDNA libraries has also documented the expression of three novel genes in freeze tolerant frogs with differential patterns of expression (organ, time, response to second messengers) whose cryoprotective actions are as yet unknown but overexpression in insect cell lines strongly improves freezing survival in vitro For more information on natural freeze tolerance go to: www.carleton.ca/~kbstorey. (Funded by the NSERC Canada)