A Steroid Driven Peripheral Oscillator in Fat Body Cells of Rhodnius prolixus (Hemiptera)

Circadian clocks are central to physiology. In animals, clocks are distributed in cells and tissues throughout the organism. The specific role of these clocks in the tissues within which they reside as well as the way they communicate and interact with each other is unclear. Using immunohistochemistry and laser confocal microscopy I have investigated whether the fat body in the insect Rhodnius prolixus contains an autonomous circadian clock. Fat body was found to express the canonical clock protein PER in a circadian fashion in vivo. However, when fat body was incubated in vitro, PER rapidly became undetectable. A pulse of ecdysteroid, but not brain neuropeptide extract, successfully induced PER expression but not cycling. Therefore, Rhodnius fat body does not seem to possess a local clock. It is inferred that PER cycling in the fat body is driven by the known rhythm of ecdysteroid concentration in the haemolymph.