Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/26/2006
Publication Date: 4/29/2006
Citation: Gahr, S.A., Weber, G.M., Rexroad III, C.E. 2006. Fasting and refeeding effects the expression of the inhibitor of dna binding (id)genes in rainbow trout (Oncorhynchus mykiss) muscle. Comparative Biochemistry and Physiology. 144:472-477. Interpretive Summary: Aquaculture production from cold water species can be greatly enhanced by increasing our understanding of the mechanisms regulating muscle growth and development. At the National Center for Cool and Cold Water Aquaculture in Leetown, WV, we have identified six members of the Inhibitor of DNA Binding/Differentiation (ID) gene family and are currently attempting to determine each of their roles in muscle growth and development in the rainbow trout. The ID genes have been characterized in mice and human studies as important regulators of muscle cell growth and development. In the current study we have determined the expression levels of the ID genes in rainbow trout muscle during seven and fourteen day fast and refeeding periods. After just seven days of fasting, the entire ID gene family was significantly lower than the fed samples. When the trout were returned to feed following the fast, we found expression of the ID genes increased to levels similar to the level in the fed fish. We present the first characterization of a vertebrate ID gene expression during a feed restriction. These data indicate the regulation of the ID genes in the muscle during a nutrient deficiency and provide preliminary information on the molecular mechanism regulating muscle mass regulation during prolonged fast.
Technical Abstract: The ID (Inhibitor of DNA Binding/Differentiation) 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 investigated 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 seven days prior to refeeding. Pooled muscle samples were collected throughout each experiment for RNA isolation. ID gene expression was determined by real-time PCR analysis. In both experiments, ID gene expression in the muscle of fasted fish was significantly lower than the fed samples after seven days. Refeeding for 3 or 7 days returned the ID expression to levels similar to the fed controls. Transcript levels in the refed samples remained at similar or slightly higher levels than the fed samples through the end of the experiment. The reduction of ID expression during a fast and the subsequent return to fed levels with refeeding suggests the ID proteins are involved in regulating the proliferative potential of the muscle cells during an extended fast in fish.