Transient NU4-targeted proteoforms manifest a third distinct pattern of expression. Retinas from embryonic days E8, E14, and E20 were stained for AβOs using the selective mouse monoclonal antibody NU4 (red). (A) E8 retina AβO immunoreactivity is localized to the NFL. (B) E14 AβO immunoreactivity is spread through all retinal layers, but is most prominent in the GCL, flanking the OPL, and in the RPE; immunoreactivity also is present in two sub-bands of the IPL and the inner and middle INL. (C) E20 retina AβO immunoreactivity is gone from most retina layers and localized to the RPE. The OPL is denoted with a star. Scale bar = 25 μm. N = 4.