Bone marrow chimeras were produced by transfer of bone marrow from FSP1.GFP transgenic mice to Balb/c wild-type mice. After 30 days of recovery, they underwent surgical UUO; kidney and bone marrow were harvested 10 days later. (a) GFP⁺ donor marrow containing FSP1⁺ stromal fibroblasts (green) and representing 5–6% of the donor cell population on FACScan were found in chimeric recipients at harvest 10 days after UUO in approximately the same proportion as in wild-type donor marrow where there was no GFP expression. (b) Tissues harvested from chimeric mice following UUO of one kidney demonstrate a rare green FSP1⁺, GFP⁺ fibroblast in the interstitium of the normal, contralateral control kidney. More fibroblasts of this type appear in the kidney stressed by UUO and fibrogenesis ×400. FSP1.GFP transgenic mice were also subjected to UUO in parallel. These UUO kidneys also showed an increase in green FSP1⁺, GFP⁺ fibroblasts compared with the contralateral control (data not shown). (c) Merged confocal microscopy of kidney sections 10 days after UUO in donor or recipient mice demonstrates a mixture of GFP⁺, HSP47^– fibroblasts (GFP shows as green), GFP^–, HSP47⁺ fibroblasts (HSP47 shows as red), and double-labeled GFP⁺, HSP47⁺ fibroblasts (green/red or weak yellow). GFP^–, HSP47⁺ tubular epithelial cells from UUO kidney tissue also stained red, reflecting their contribution to collagen type I production during EMT. ×630.