Decreased BrdU incorporation into endothelial cells in Rap1b^−/−retinas. (A) Low-magnification image (left micrograph) is a composite of confocal images comprising a quarter of the retina isolated from a P7 Rap1b^+/− mouse, which had been injected intraperitoneally with BrdU and stained with Texas red–conjugated isolectin (endothelium, red) and FITC-conjugated anti-BrdU antibody (nuclei, green). Bar represents 500 μm. Boxed area is enlarged (insert) to better show the detail of nuclear staining by BrdU. Bar represents 50 μm. Lines have been inserted to indicate sections of the composite image. (B) Quantification of all BrdU-positive nuclei in one quarter of a retina from each analyzed pup. Plotted are data from Rap1b^+/+ (WT), Rap1b^+/− (Het), and Rap1b^−/− (KO) mice. For each dataset, the box shows 25th to 75th percentile range and median. Whiskers extend to the 10th and 90th percentile, and standard error of the mean is plotted. The number of dividing endothelial cells was significantly reduced in Rap1b^−/− versus normal retinas (284 ± 75 vs 543 ± 101; n = 6; P < .05).