Asleep at the Wheel: Forward Genetic ENU Mutagenesis Screen for Mouse Models of Chronic Fatigue Identifies a Mutation in Slc2a4 (GLUT4)

Abstract

ABSTRACTIn a screen of voluntary wheel-running behavior designed to identify genetic mouse models of chronic fatigue in ENU mutagenized C57BL/6J mice, we discovered two lines that showed aberrant wheel-running patterns. These lines both stem from a single original founder identified as a low body-weight candidate in a recessive screen. Progeny from both of these lines showed the abnormal wheel-running behavior, with affected mice showing significantly lower daily activity levels than unaffected mice. They also exhibited low amplitude circadian rhythms, consisting of lower activity levels during the normal active phase, and increased levels of activity during the rest or light phase, but only a modest alteration in free-running period. Their activity is not consolidated into longer bouts, but is frequently interrupted with periods of inactivity throughout the dark phase of the light-dark (LD) cycle. As seen with the low body weight, expression of the behavioral phenotypes in offspring of strategic crosses was consistent with a recessive heritance pattern. Mapping of these phenotypic abnormalities showed linkage to a single locus on chromosome 11, and whole exome sequencing (WES) identified a single point mutation in the Slc2a4 gene encoding the GLUT4 insulin-responsive glucose transporter. The single nucleotide change (A to T) was found in the distal end of exon 10, and results in a premature stop (Y440*). To our knowledge, this is the first time a mutation in this gene has been shown to result in extensive changes in general behavioral patterns.SIGNIFICANCE STATEMENTChronic fatigue is a debilitating and devastating disorder with widespread consequences for both the patient and the persons around them, but effective treatment strategies are lacking. The identification of novel genetic mouse models of chronic fatigue may prove invaluable for the study of its underlying physiological mechanisms and for the testing of treatments and interventions. A novel mutation in Slc2a4 (GLUT4) was identified in a forward mutagenesis screen because affected mice showed abnormal daily patterns and levels of wheel running consistent with chronic fatigue. This new mouse model may shed light on the pathophysiology of chronic fatigue.