Figure 4. Immunohistochemical analysis of Syt1 expression changes in ERU retina.

Left panels: representative healthy retina; right panels: representative ERU case. Differential interference contrast images of healthy (A) and ERU affected (B) retinal specimen demonstrating that in ERU state, normal retinal architecture is disturbed. GRP78 (green color), a marker staining retinal ganglion cells and a population of inner nuclear layer cells in equine retina was equally expressed in physiological (C) and ERU state (D). Synaptotagmin-1 (Syt1, red color) signal in healthy retina (E) was most prominent in retinal ganglion cell somata, their axons in the nerve fiber layer and in somata of a cell population in the inner nuclear layer, with additional staining foci in the outer and inner plexiform layer and photoreceptor outer segments, while ERU affected retinal sections (F), presented with a clearly reduced overall Syt1 signal. Overlay of GRP78 and Syt1 signals (G: healthy, H: ERU) indicated that in the ERU affected section, Syt1 expression is reduced, although structures expressing it in physiological state are still present. Cell nuclei were counterstained with DAPI (blue color).