Fasting and refeeding affect the expression of the Inhibitor of DNA Binding (ID) genes in rainbow trout (Oncorhynchus mykiss) muscle

The Inhibitor of DNA Binding/Differentiation (ID) proteins are a family of dominant negative regulators of the basic helix-loop-helix (bHLH) transcription factors, shown in mammals to delay cell differentiation and prolong proliferation. In the current study we used real-time PCR to investigate the effects of fasting and refeeding on the expression of ID genes in rainbow trout muscle. Fry shortly following yolk-sac absorption (∼ 250 mg) were used in a pair of experiments. In the first experiment, the treatment groups included fish fed or fasted throughout the duration of the experiment, and fish fasted for 14 days followed by feeding for the remainder of the experiment. The second experiment consisted of the same treatment groups; however the fish were only fasted for 7 days prior to refeeding. In both experiments, ID gene expression in the muscle of fasted fish was significantly lower than the fed samples after 7 days. Refeeding for 3 or 7 days returned the ID expression to levels similar to the fed fish. The reduction of ID expression during a fast and the subsequent return to fed levels with refeeding suggests the ID proteins participate in the regulation of muscle growth in the rainbow trout.