Figure 4. S1P₂R modulates retinal vascular patterning.

(A and C) At P14, S1p2^+/– and S1p2^–/– retinas optically sectioned at the GCL showed similar distribution of proliferative cells (BrdU staining). At P17, S1p2^+/+ retinas (B) optically sectioned at the GCL showed an increased number of proliferative cells (BrdU staining) colocalizing with ECs (E, GS-lectin, white arrowhead) in the vascular tuft areas, while in S1p2^–/– retinas (D), mitogenic cells were incorporated into the central vascular bed (F, ECs–GS-lectin, white arrowhead). (G) Quantification of fluorescent pixels representing BrdU-positive cells per retina at P14: S1p2^+/– retinas showed 0.05 ± 0.006 (n = 5), whereas S1p2^–/– retinas showed 0.05 ± 0.011 (n = 5; *P = 0.47) fluorescent pixels/total retinal area. At P15, S1p2^+/+ retinas favored excessive growth of neovascular tufts into the vitreous (H), whereas S1p2^–/– retinas favored vascular sprouts directed into the central retina (tip cells, arrows) (I). At P17, S1p2^–/– retinas optically sectioned at the GCL presented enhanced normal revascularization with endothelial tip cells (inset) redirected into the ischemic retina area (K), whereas S1p2^+/+ retinas formed abnormal vascular buds directed toward the vitreous chamber (J, inset). (L) At the early stage of retina pathogenesis (P15), S1p2^+/– retinas developed 23.122 ± 5.73 tip cells/field (n = 9), whereas S1p2^–/– retinas developed 34.34 ± 6.3 tip cells/field (n = 7; ^†P < 0.0025). Values represent mean ± SD. Scale bars: 200 μm (A–D, H, and I), 20 μm (E and F), and 50 μm (J and K).