PI3Kβ loss inhibits the induction of apelin expression in vivo. Wild-type littermates or β^ECKO mice were treated with the lectin-saporin cytotoxin as in Figure 1, then kidney tissue was harvested at day 3 and immunostained for apelin expression (A). Uninjured kidney glomeruli show little apelin staining. Toxin-mediated EC injury induces glomerular apelin expression (middle panel, arrows) in wild-type, but not β^ECKO, mice. The frequency of glomeruli expressing apelin is quantitated (B) (mean ± SEM; n = 4 mice/group; *P < .05 by ANOVA).