Morphology of renal Epo-producing (REP) cells expressing the wt-Epo-GFP transgene. Immunohistochemical staining was carried out with anti-GFP antibody of normal (A) and anemic (B-D) mouse kidneys from transgenic line WA (A,B,D) and wild-type (C) mice. GFP expression (brown) was detected in the peritubular interstitial cells (arrows in B,D) with long projections (arrowheads in D) between the proximal tubules (PT) and vessels (V). Fluorescent images of REP cells from anemic kidneys of transgenic mice (line WA) taken with the confocal laser scanning microscope (E-I). When costained with cell lineage markers (red), REP cells (green) were negative for CD31 (F) and Mac1 (G), but positive for MAP2 (H) and NFL (I). Scale bars represent 50 μm (A-C) and 10 μm (D-I).