Mice lacking insulin receptor substrate 4 exhibit mild defects in growth, reproduction, and glucose homeostasis

The insulin receptor substrates (IRSs) function in insulin signaling. Four members of the family, IRS-1 through IRS-4, are known. Previously, mice wit h targeted disruption of the genes for IRS-1, -2, and -3 have been characte rized. To examine the physiological role of IRS-4, we have generated and ch aracterized mice lacking IRS-4. Male IRS-4-null mice were similar to 10% sm aller in size than wild-type male mice at 9 wk of age and beyond, whereas t he female null mice were of normal size. Breeding pairs of IRS-4-null mice reproduced less well than wild-type mice. IRS-4-null mice exhibited slightl y lower blood glucose concentration than the wild-type mice in both the fas ted and fed states, but the plasma insulin concentrations of the IRS-4-null mice in the fasted and fed states were normal. IRS-4-null mice also showed a slightly impaired response in the oral glucose tolerance test. Thus the absence of IRS-4 caused mild defects in growth, reproduction, and glucose h omeostasis.