Expression of APP in APP-ibl mouse brain in the presence or absence of X11L. (A) Expression of human APP695swe and mouse endogenous APP695. Brain regions composed of the cerebral cortex, hippocampus and olfactory bulb from wild-type (WT), APP-ibl and APP-ibl/X11L-Ko mice (4 months old) were homogenized in 10 mM Tris-HCl [pH 7.9] containing 1% (w/v) SDS, 4 M urea, complete protease inhibitor cocktail (Roche Diagnostics), and 1 μM pepstatin. The lysates were analyzed by immunoblotting with anti-human APP (10D1), anti-APP (8717), anti-X11L and anti-α-tubulin antibodies. (B) The densities of human APP695swe (left) and human plus mouse APP (right) bands were standardized to the density of α-tubulin, which was compared with the ratios for APP-ibl mice (left) or wild-type mice (right), which were assigned a reference value of 1.0 (values represent means ± S.E.). The data were analyzed by Student's t test (n = 3).