R-cadherin-specific cyclic IDS peptides prevent normal EPC targeting to the developing retinal vasculature. (A) Planar images of the 3 normal retinal vascular plexuses and the outer edge of the photoreceptor layer demonstrated massive HSC mistargeting caused by R-cadherin-specific peptide antagonists (cyclic IDS), similar to the effects observed by preincubation with R-cadherin function-blocking antibodies. HSCs were mistargeted to the subretinal space rather than the superficial, intermediate, or deep vascular plexuses, compared to cyclic INP-incubated, or normal, Lin^- HSCs. A small portion of mistargeted HSCs were incorporated into regions of mistargeted endogenous vasculature (insert). Scale bar represents approximately 50 μm. Original magnification of inset × 60. (B, C) Analysis of frozen retinal sections demonstrated normal targeting (B, black lines) of HSCs preincubated with cyclic INP and mistargeting (C, red lines) of HSCs to the outer edge of the photoreceptors after preincubation with cyclic IDS peptides. Scale bar represents approximately 50 μm. (D) The number of HSCs targeted to the 3 normal vascular plexuses or mistargeted to the outer edge of the photoreceptor layer was quantified as a relative percentage of the total number of retinally incorporated HSCs. Preincubation with cyclic IDS peptides greatly disrupted HSCs targeting, particularly to the intermediate and deep plexuses (P < .01, star), and greatly increased the number of mistargeted HSCs localized within the subretinal space (P < .0001, star). Error bars indicate standard deviation.