PODRABSKY, J.E.*; SOMERO, G.N.: Changes in Gene Expression Associated with Diurnal Temperature Cycling in the Annual Killifish Austrofundulus limnaeus

Annual killifish thrive in small ephemeral ponds that experience wide fluctuations in temperature (22-39&degC) on a diurnal basis. The biochemical and molecular mechanisms that maintain cellular homeostasis during such temperature fluctuations are largely unknown. We are investigating changes in gene expression associated with a cycling temperature regime using cDNA microarray analysis. A microarray was prepared using full-length cDNA sequences isolated from a normalized cDNA library and a subtracted cDNA library enriched for differentially expressed cDNAs. Two tissues were chosen for the initial analysis, liver and white muscle. Adult annual killifish Austrofundulus limnaeus were exposed to three different thermal treatments: a cycling temperature regime of 20-37&degC on a daily basis, constant exposure to 20&degC, and constant exposure to 37&degC. Control fish were kept at 26&degC. Differentially expressed cDNAs were identified by probing the cDNA microarray with fluorescent-labeled probes prepared from total RNA isolated from fish exposed to the various thermal regimes. These cDNAs were then sequenced and identified by homology to known genes or gene products using the Blastx database search engine. Patterns of gene expression are being used to construct a global view of physiological and biochemical responses to diurnal temperature cycling as well as to identify new genes and generate new hypotheses concerning the molecular basis of eurythermality.