The circadian clock is a conserved internal timekeeping mechanism that controls many aspects of physiology and behavior via the rhythmic expression of many genes. One of these rhythmic genes, Nocturnin, encodes a deadenylase-a ribonuclease that specifically removes the poly(A) tails from mRNAs. This enzyme is expressed at high levels during the night in a number of tissues in mammals and has recently been implicated in circadian control of metabolism. Targeted ablation of this gene in mice results in resistance to hepatic steatosis and diet-induced obesity. Nocturnin appears to exert rhythmic posttranscriptional control of genes necessary for metabolic functions including nutrient absorption, glucose/insulin sensitivity, and lipid storage. In the Western world and many developing countries, overnutrition-the 'obesity epidemic' suggests that the ability to sequester fat stores in times of plenty is no longer advantageous to our survival. Understanding the role that the circadian clock plays in controlling these metabolic processes is important in treatment and eventual eradication of this public health crisis.
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