(A) Schematic of parabiotic experiments. (B and C) Localization of tdTomato+ CX3CR1-lineage cells in Cx3cr1GFP kidneys. The tdTomato-positive cells were lineage-labeled in Cx3cr1CreERt; Rosa26tdTomato mice in utero at E9.5. They migrated into the parabiont Cx3cr1GFP kidneys from circulation. Note that tdTomato+ cells were detected in extravascular interstitium (n = 4 per group). Endomucin; an endothelial cell marker. *, lumen of capillaries. Arrowheads, CX3CR1-lineage cells from circulation. (D and E) Circulation-derived CX3CR1-lineage cells proliferate in adult kidneys. Arrowheads, CX3CR1-lineage cells from circulation. GFP fluorescence was lost during the antigen retrieval process to detect Ki67. Percentages of Ki67+tdTomato+ cells relative to tdTomato+ cells in the kidneys of indicated genotype are shown in E (n = 4 per group). Note that tdTomato+ cells in Cx3cr1GFP kidneys are derived from circulation. Data are represented as means ± S.D. *, p<0.05. Scale bars: 10 μm in B and C; and in 20 μm in D. Legends for the Supplementary Figures.