Temperature throws a developmental switch

A tantalizing task in the postgenomic era is to decipher the basis of gene–environment interactions or, to phrase it more explicitly, How do environmental cues regulate decisions on organismal developmental fate? In PNAS, Romney et al. (1) shine some light on how a developmental decision can be influenced by external stimuli in an annual killifish. One very obvious environmental signal is temperature. A well-known example of a gene–environment interaction is temperature-dependent sex determination in turtles and crocodilians. In this case, the temperature of the eggs in a specific time window during development is the decisive factor in determining sex. Small changes in temperature can cause dramatic changes in sex ratio (2). Although the precise mechanism of temperature-dependent sex determination is not yet clear, it has been shown that the temperature-sensitive activity of aromatase, an enzyme that is responsible for a key step in the synthesis of the steroid hormone estradiol, is a critical factor (3). Another example of a binary, organism-wide switch relates to even earlier embryonic development. A number of animals can suspend development during periods of adverse environmental conditions. One example is the roundworm Caenorhabditis elegans that normally proceeds through four larval stages before it becomes an adult animal. Under conditions of overcrowding, high temperature, or food deprivation, a C. elegans larva can enter a stage of developmental arrest called dauer. A similar state of developmental arrest can be found in annual killifishes like Nothobranchius furzeri and Austrofundulus limnaeus that live in Africa and South America, respectively, and have recently become models for research on aging and on developmental stress tolerance (4, 5). Both species inhabit seasonal freshwater ponds that desiccate annually during the dry season and refill during the wet season. The life cycle of annual killifishes is greatly adapted to the ephemeral nature of … [↵][1]1Email: christoph.englert{at}leibniz-fli.de. [1]: #xref-corresp-1-1