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.