Figure 5. A-S, CD90+ MSC fate 1-12 weeks after transplantation. A, CD90+ MSCs were prelabeled with BrdU before injection (400×). B-E, H, Hematoxylin and eosin (H, E) staining of retinas 7 d after transplantation (B-D) revealed a large number of CD90+ MSCs in the subretinal space at the site of injection (B, arrow) (100×), with only slight disruption to the host retina (C, arrow) (200×) occurring at the site of injection. Retina distant to the injection site (D) (200×) revealed normal structural integrity. E, Retinas 5 weeks after transplantation histologically appeared normal with very little disruption to the host (200×). Pockets of CD90+ MSCs were observed still in the subretinal space, although these were observed primarily at the site of injection (arrow) (200×).G, I, Detection of BrdU-labeled CD90+ MSCs in the ON at the site of injection at 7d (G)(300×) and 5 weeks (I) after transplantation (300×). F,H, Retina distant to the injection site appeared normal and did not contain any transplanted cells at 7d (F)(300×)and 5 weeks (H) (300×) after transplantation. Even 5 weeks after transplantation, CD90+ cells were still primarily found within the ON (J) (200×), adjacent to the injection site of host retinas. K, Expression of the photoreceptor-specific marker opsin revealed typical outer segment staining in nontransplanted retinas (300×). L, A similar pattern of opsin expression in host retina distant to the injection site (100×). M, At the injection site, the outer segment staining becomes less apparent, because the structural hierarchy of the host retina is not fully restored after transplantation but is primarily expressed in the cytoplasm of cells located within the injection site (100×). N, Higher magnification of the injection site revealed the cytoplasmic expression of opsin in these cells (400×). O, Transplanted cells were identified by the coexpression of BrdU (green) and opsin (red) with in the injection site (1000×; inset, 2000×). Bottom arrows highlight two injected MSCs that were immunoreactive for BrdU and the RHOS antibodies. The top arrow indicates an endogenous photoreceptor whose opsin expression had been translocated to its cytoplasm as a result of the injection procedure. P, Synaptophysin expression in nontransplanted retina typically stains positive (indicated as red) in the outer plexiform and ganglion cell layers (100×). Q, Higher magnification reveals the colocalization of BrdU and synaptophysin in CD90+ MSC-transplanted retina (1000×). R, Immunohistochemical analysis of transplanted retina revealed that the majority of BrdU-labeled cells was located at the proximal end of the ON, adjacent to the OPL (1000×). S, Electron microscopic analysis of these cells revealed synaptic vesicle formation(arrows)(31,200×). G, Ganglionic cell layer; IN, inner nuclear layer; OPL, outer plexiform layer; OS outer segments.