PKHD1 and autosomal dominant polycystic kidney disease: We found that DDR1 protein and activity (assessed by anti-phospho-DDR1 antibodies) was increased in kidneys from 3 mouse models of ADPKD that included 2 “early, rapid” models in which Cre is driven by Pkhd1 (Pkhd1-Cre; Pkd1fl/fl) and aquaporin (Aqp2-Cre; Pkd1fl/fl, not shown) and in the “late, slow” Pax8rtTA; TetO-Cre; Pkd1fl/fl model (Fig 1A).