The data show that this relative levels ofEph-A6at the five sample locations change between Fd55 and Fd80, but that by Fd110 a pattern of expression is established where peak levels ofEph-A6mRNA are detected in the ganglion cell layer (GCL) at the fovea. gradient ofEph-A6expression was high near the optic disc and low at the developing macula at fetal day (Fd) 55. At Fd 70 and 80, the gradient ofEph-A6expression was reversed, being higher temporal to the macula, and low at the disc. By Fd 110, when the fovea begins to form, a pattern of expression was established that persisted into the postnatal period, in which the highest levels of expression were detected at the developing fovea, OSI-906 and progressively lower levels of expression were detected at increasing distance from your fovea. Beginning at Fd 70, we also detected a gradient ofEph-A6expression running perpendicular to the retinal surface within the GCL of central retina that was high in the inner GCL and low in the outer GCL. This second pattern persisted into the neonatal period. We found the two ligands forEph-A6,ephrin-A1andephrin-A4, expressed byPax2-immunoreactive astrocytes, in the optic nerve head and in the retina, by in situ hybridization and immunohistochemistry. We propose that during development of the retinal vasculature, migration of ligand-bearing astrocytes is usually slowed along thisEph-A6expression gradient through repellentEph-A6-ephrin-A1and-A4signaling. == Conclusions == Patterns ofEph-A6expression in the developing macaque retina suggest thatEph-A6 – ephrin-A1and-A4repellent signaling has a role in retinal vascular patterning, and in the postnatal maintenance of projections from macular and foveal GC. == Introduction == The fovea centralis (fovea) is usually created in temporal retina during late fetal life by the centrifugal displacement of cells OSI-906 of the inner retina, leaving cone cell body lining the floor of the pit. The fovea is usually centrally placed in the less well defined macula. The macula is usually a region approximately 3 mm in diameter recognized clinically by its high concentration of yellow, xanthophyll pigments (hence, macula lutea) and a relative absence of large diameter retinal vessels. In this region, the neural retina is also highly specialized: the density of all neural elements is usually elevated; there is a peak spatial density of cone photoreceptors; you will find no rods; and there is a prevalence of midget or parvocellular circuitry [1-3]. Signals encoded by these circuits provide the brain with the detailed spatial and color information, characteristic of macular visual function. Absence of large retinal vessels from your macula is an adaptive advantage, since large vessels cause shadowing of the cone mosaic [4] and if present, would degrade the quality of the image that OSI-906 strikes the high density cone array. Under normal circumstances the foveal region is by no means vascularized [5] and remains so throughout life. Despite this, the principal retinal angiogenic factor, vascular endothelial growth factor (VEGF), MTRF1 is usually highly expressed at the macula during development of the retinal vessels [6,7], so it is usually a paradox that macular vessels OSI-906 are slow to develop [8,9]. These observations led us to the hypothesis that repellent guidance cues might inhibit the migration of endothelial cells, and astrocytes, into OSI-906 the macular region during development. Three lines of evidence led us to investigate the expression patterns of Eph receptors and their ligands. First, Eph receptor signaling has an important role in retinal axon pathfinding [10-13] and retinal vessels follow trajectories much like those taken by retinal axons [14,15]. Second, development of retinal vessels is dependent on Eph receptor signaling [16-19]. Third, in a microarray analysis of differential gene expression in the developing human macula [20], we found higher levels of expression ofEph-A6in the macula, confirmed by quantitative RTPCR. In the present study we aimed to identify the expression patterns ofEph-A6and its ligands in the developing macaque retina. == Methods == == Specimens == We used histological sections of retinas from 10 macaques at fetal days (Fd) 55, 64, 70, 80, 110, 115, 120, 145, postnatal day (P) 5, and P 3 months. This developmental range straddles the period during which the perifoveal capillaries form and the foveal avascular area is defined, that is, between about Fd 90 and several days postnatal [9]. The sections were obtained by A.E. Hendrickson from your breeding colony of.
