March 8, 2006 — Many reptiles in the wild can survive for days, even when over half of their body water is frozen, and now scientists have identified three groups of genes that help keep these animals from sustaining damage or death during this near-Popsicle condition.

The discovery not only helps to solve the reptile freezing mystery, but scientists also hope the research could one day lead to improved methods for freezing human cells and organs so that tissues in cryostorage could remain alive and viable after thawing.

When the temperature dips, some reptiles cannot escape to warmer areas, so several species instead have evolved incredible tolerance to cold.

"Over the past 20 or more years of working in the field, various researchers, including ourselves, have come to realize that animals that survive long-term freezing as an integral part of their winter survival strategy have to be able to deal with ice penetration throughout their whole body and with the many consequences of this, including blood plasma freezing, heart beat and breathing stopping, etc.," said Janet Storey, a research associate at Carleton University's Institute of Biochemistry in Canada.

She assisted Kenneth Storey, who outlined the research in a paper published in the current issue of Cryobiology.

The scientists carefully froze hatchling painted turtles, Chrysemys picta marginata. They observed that ice first formed in spaces around major organs, such as in brain ventricles and the abdomen.

When thawed, the organs defrosted more rapidly than did the ice that surrounded them.

The researchers then analyzed DNA from the turtles' heart and liver cells. They discovered that the turtles possess a remarkable antioxidant defense system.

Storey explained to Discovery News, "Oxygen is good because it is the substrate for respiration, but oxygen can also be bad because it gives rise to various reactive oxygen species in both spontaneous chemical reactions that cells have little control over and enzymatic reactions where a reactive oxygen species (ROS) is a product."

She said that when humans suffer a heart attack or stroke, oxygen deprivation usually does not cause most of the damage, but rather it is the rise in ROS after the event that often creates problems.