Some days, choosing the right clothes isn't easy. It might be freezing when you leave home, but once the sun's beating down, some early morning sartorial choices might not seem so wise. And if we find diurnal temperature fluctuations stressful, spare a thought for the tiny annual killifish, trapped in its coastal desert ponds; they routinely weather 20°C temperature fluctuations. Jason Podrabsky and George Somero are fascinated by the physiological adaptations that allow creatures to survive and thrive under extreme environmental variations. Curious how the little fish's gene expression patterns change under several thermal conditions, they designed a novel gene chip, coated with 4992 killifish liver genes, to find out how the fish faired after acclimation at 20°, 26° and 37°C, and a daily temperature cycle ranging from 20–37°C over a 2 week period(p. 2237).

Using the custom made gene chip to compare mRNA samples from fish exposed to one of the four temperature regimes, with mRNA from control fish, Podrabsky and Somero found that 540 genes changed their expression patterns significantly, with different patterns in the fish exposed to a daily temperature cycle compared with fish acclimated to constant temperatures.

Grouping the genes according to their cellular functions, Podrabsky found that molecular chaperones, membrane structure and solute transporters were all affected by the temperature treatments, as well as various metabolic genes,cytoskeletal genes, genes involved in protein turnover, immune response and cell growth. Some of the genes which responded to temperature haven't even been assigned functions yet, and Podrabsky is excited by the possibility of discovering new temperature sensitive factors and pathways.

But Podrabsky is most intrigued by a single transcriptional regulator,HMGB1, which decreases its transcriptional levels tenfold as the temperature rises daily. Podrabsky suspects `HMGB1 protein may be... a highly sensitive temperature sensor' by causing a `global change in the rate of transcription'.

Podrabsky, J. E. and Somero, G. N. (
). Changes in gene expression associated with acclimation to constant temperatures and fluctuating daily temperatures in an annual killifish Austrofundulus limnaeus.
J. Exp. Biol.