Localization of PRA1-LIR in wt and rd1 retina. Immunofluorescence labeling was performed on cryostat sections of mouse retinas harvested at P6 (A – C), P8 (D – F), P10 (G – I), and P21 (J – L). No staining was seen in control (ctl) sections processed without primary antibody (A, D, G, and J). In wt retinas (B, E, H, and K), PRA1-LIR was seen in photoreceptor inner segments (IS), particularly in the proximal region and in streaks through the outer nuclear layer (ONL) during differentiation, consistent with the growth of apical processes. These streaks were no longer present in the mature retina at P21 (K). In rd1 retinas (C, F, I, and L), PRA1-LIR was also present in IS but appeared less intense and more diffusely distributed. Insets, taken from an adjacent area to avoid bleaching, illustrate at 4× higher magnification the inner segment region, which is indicated between the bars on the right margin. In both genotypes, PRA1-LIR was seen in the perinuclear region of most inner retinal neurons and in both plexiform layers with increasing intensity during development. However, at P21 staining was more diffuse in the inner rd1 retina (L) compared to wt (K). Images are representative stacks of 6 confocal slices. Abbreviations: OPL = outer plexiform layer, INL = inner nuclear layer, IPL = inner plexiform layer, GCL = ganglion cell layer.