Molecular mechanisms linking energy metabolism and thermoregulation

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For ectothermic animals, behavior plays a major role in thermoregulation; a wide variety of animals sense the environmental temperature and move towards to thermally comfortable zone. Although most ectothermic animals do not use metabolically produced heat to regulate body temperature, we found that thermoregulatory behavior of Drosophila is highly dependent on the level of energy metabolism; the increase in mitochondrial oxidative phosphorylation induced preference for the low temperature (Science 323:1740-1743, 2009), while the suppression of energy metabolism by inhibiting insulin signaling caused a warm-seeking thermoregulatory behavior. During the course of identifying molecules involved in the control of energy homeostasis, we found that delta-9 fatty acid desaturase (desat1) expressed in the fat body, a tissue equivalent to mammalian liver and adipose tissue, played a pivotal role in the control of energy metabolism as well as thermoregulatory behavior. Defective expression of desat1 suppressed mitochondrial oxidative phosphorylation, causing a significant decrease in body size and warm-seeking phenotype. In contrast, induced expression of delta-12 fatty acid desaturase (Caenorhabditis elegansFat-2) that produces linoleic acid caused the increase in body size and the low-temperature preference. These observations suggest that the changes in lipid desaturation coordinately regulate mitochondrial energy metabolism and thermoregulatory behavior.