Survival of intracellular freezing by the Antarctic nematode Panagrolaimus davidi

Animals are usually thought to survive ice formation in their bodies only if the ice is confined to the body cavity and to extracellular spaces. Intracellular ice formation is believed to be fatal. This conclusion is based on studies of the cryopreservation of mammalian cells. Intracellular freezing has been observed in some living insect cells but has not been observed in intact animals. Nematodes are transparent and so the location of ice in their bodies can be observed directly using a cryomicroscope stage. We have observed freezing and melting in all body compartments, including intracellular compartments, of the Antarctic nematode Panagrolaimus davidi. Inoculative freezing from the surrounding water occurs via the body openings, rather than across the cuticle; most frequently it occurs via the excretory pore. Individual nematodes that have frozen intracellularly will subsequently grow and reproduce in culture. Determining the mechanisms by which this nematode survives intracellular freezing could have important applications in the cryopreservation of a variety of biological materials.