March 9, 2010 vol. 107 no. 10 4487–4790 Proceedings of the National Academy of Sciences of the United States of America www.pnas.org PNAS In This Issue PNAS March 9, 2010 vol. 107 no. 10 4487–4488 www.pnas.org/cgi/doi/10.1073/iti1010107 Cryopreservation of biological materials often depends on the rapid removal of water from the material to be preserved. Re- searchers have long preserved cells and tissues in a vitrified state by suspending them in cryoprotectant liquids before im- mersing them in liquid nitrogen. Vitrification keeps cells meta- bolically dormant and helps avoid the formation of ice crystals, which could damage cells. To determine the factors that drive vitrification, Young Song et al. (pp. 4596–4600) studied the physical phenomena that occur when a droplet of the cryopro- tectant 1,2-propanediol plummets into liquid nitrogen. When ejected into liquid nitrogen, the droplet rises to the surface, buoyed by a vapor cloud generated by the evaporation of the surrounding liquid nitrogen. After skittering around on the surface, the droplet sinks when its temperature reaches that of liquid nitrogen, in a similar fashion to water sprinkled on a hot skillet. Using mathematical modeling, the authors found that the size, temperature, and composition of the droplet determine whether the droplet gets vitrified or crystallized. The findings could enable the development of high-throughput, automated methods of cryopreservation of biologi- cal samples such as blood and oocytes, according to the authors. — P.N. Atrazine can induce chemical castration in male frogs Modeling phase transition in levitating droplets In 2004, the European Union banned atrazine, the most com- monly used pesticide in the world, because of research linking it to endocrine disruptions in amphibians and other animals. However, the US Environmental Protection Agency (EPA) concluded in 2006 that there was insufficient data to determine whether atrazine affects amphib- ian development. Tyrone Hayes et al. (pp. 4612–4617) examined the long-term effects of atrazine exposure on reproductive function and development in an all-male population of African clawed frogs and report that atrazine induced feminization and chemical castration in some of the animals. The authors com- pared 40 control frogs with 40 frogs reared from hatching until sexual maturity, both living in an environment with a 2.5 ppb atrazine concentration, which is in the range that animals experience in areas where the pesticide is found and is below EPA drinking water standards. All the adult control frogs showed male-typical external features, whereas four of the other group of frogs had some female-typical features. Two of these frogs had ovaries, and the other two successfully mated with male frogs and produced viable eggs. The atrazine-exposed frogs suffered from depressed testosterone levels, decreased breeding gland size, demasculinized la- ryngeal development, suppressed mating behavior, reduced spermatogenesis, and decreased fertility. These data provide evidence that atrazine may play a role in declining amphibian populations, according to the authors. — B.A. Converting cellulose into ethanol Researchers have developed a method of processing cel- lulose from plants and other non-edible natural products into individual sugar molecules that then can be fermented by bacteria to produce ethanol. Plant cellulose contains long chains of useful sugars that store plenty of energy, but it is largely inaccessible due to the difficulty of breaking down cellulose. Joseph Binder and Ronald Raines (pp. 4516–4521) converted cellulose to simple sugars with a combination of an ionic liquid, acid, and chroma- tography and suggest that their technique could be developed into a large-scale industrial pro- cess to produce biofuel or other products. After the completion of the short (approximately 2–4 A droplet levitating on top of liquid nitrogen. Two genetic male African clawed frogs copulating. Downloaded by guest on August 29, 2021