Gradients of Eph-A6 expression in primate retina suggest roles in both vascular and axon guidance

[摘要] Purpose: Recently we identified highlevels of expression of Eph-A6 in the macula of developinghuman retina and showed localization of Eph-A6 to ganglioncells (GC). In the present study we investigated the expression of somemembers of the ephrin family in developing primate retina, includingthe topography of Eph-A6 expression, and its ligands, indeveloping macaque retinas. Methods: We extracted RNA from humanfetal retinas and probed for Eph-A5–A7, Eph-B1, ephrin-B2,and ephrin-A1-A5 by RT–PCR, then prepared riboprobes for Eph-A5-A7,Eph-B1 and ephrin-A1, -A4 and -B2. Paraffinsections of fetal macaque retinas were used to localize expression ofEphs and ephrins by in situ hybridization and immunohistochemistry. Results: We identified prominentgradients of Eph-A6 mRNA expression in the ganglion cell layer(GCL) of fetal macaque retinas of different ages. The gradient of Eph-A6expression was high near the optic disc and low at the developingmacula at fetal day (Fd) 55. At Fd 70 and 80, the gradient of Eph-A6expression was reversed, being higher temporal to the macula, and lowat the disc. By Fd 110, when the fovea begins to form, a pattern ofexpression was established that persisted into the postnatal period, inwhich the highest levels of expression were detected at the developingfovea, and progressively lower levels of expression were detected atincreasing distance from the fovea. Beginning at Fd 70, we alsodetected a gradient of Eph-A6 expression running perpendicularto the retinal surface within the GCL of central retina that was highin the inner GCL and low in the outer GCL. This second patternpersisted into the neonatal period. We found the two ligands for Eph-A6,ephrin-A1 and ephrin-A4, expressed by Pax2-immunoreactiveastrocytes, in the optic nerve head and in the retina, by in situhybridization and immunohistochemistry. We propose that duringdevelopment of the retinal vasculature, migration of ligand-bearingastrocytes is slowed along this Eph-A6 expression gradientthrough repellent Eph-A6 - ephrin-A1 and -A4signaling. Conclusions: Patterns of Eph-A6expression in the developing macaque retina suggest that Eph-A6 -ephrin-A1 and -A4 repellent signaling has a role in retinalvascular patterning, and in the postnatal maintenance of projectionsfrom macular and foveal GC.

[学科分类] 生物化学/生物物理