COL4A3 and chronic kidney disease: Consistently, bone mRNA expressions of osteoblast markers (Runx2, Sp7, Bglap, and Phex) were all reduced in B6 Col4a3−/− compared to WT controls (Figure S1a), and primary osteoblasts isolated from B6 Col4a3−/− bones also showed reduced mineralization in vitro compared to WT osteoblasts (Figure S1,b-c), suggesting intrinsic alterations of osteoblast differentiation in CKD.