Functional knockout of the glucose transporter 2 in mice overexpressing a dominant negative mutation

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Fanconi-Bickel syndrome (FBS) is an autosomal recessive disorder characterized by hepatorenal glycogen accumulation, Fanconi nephropathy and impaired utilization of glucose and galactose. Recently several mutations in GLUT2 gene were reported in FBS patients. We performed molecular analysis of three Japanese patients and found four novel mutations : a splice-site mutation (IVS2-2A>G), a nonsense mutation (Q287X) and two missense mutations (L389P and V423E). The family members who presented renal glucosuria were heterozygous for V423E mutation. If some mutant GLUT2 proteins such as V423E have a dominant-negative effect, an oligomer composed of mutant and wild-type proteins could result in abolition of transport activity.In this experiment, we tried to create model mouse for Fanconi-Bickel syndrome using functional knockout by overexpression of dominant negative inhibitor. The expression vector consists of the CAG promoter, a loxP, the DsRed, a second loxP, the mutant GLUT2 cDNA (V423E), the IRES, and the EGFP, in that order. The CDRE-GLUT2 unit was excised and microinjected into fertilized mouse eggs. We finally obtained 4 different strains, which over expressed mutant GLUT2 cDNA. We measured the blood glucose levels of these mice and checked the glucosuria but there were no significant difference between control mice and transgenic mice. We speculated that expression of mutant GLUT2 in transgenic mice was not enough to produce functional knockout or that V423E mutation had not dominant-negative effects.