Circadian expression of the clock gene Per2 is altered in the ruin lizard (Podarcis sicula) when temperature changes.

When exposed to the cold, the body temperature of the ruin lizard (Podarcis sicula), an ectothermic vertebrate, comes into equilibrium with that low environmental temperature. During this time, the behavioral output of the circadian clock, locomotor activity, disappears. We tested the activity of the circadian clockwork at low temperature (6 degrees C) by following the expression of one of its essential components, the Period2 (Per2) gene. Here we show that lizard Per2 (lPer2) expression, which is rhythmic and paralleling the behavioral rhythm of locomotor activity at higher temperature (29 degrees C), becomes constantly high at low temperature. When lizards are re-exposed to high temperature, rhythmic lPer2 expression is re-established after 2 days of adaptation and coincides with onset of locomotor activity. The alteration of the lPer2 expression pattern at low temperature indicates that the activity of the molecular feedback loop is modified under these conditions.