NRL and retinitis pigmentosa 1: The presence of relatively early NRL-positive rods, cone arrestin-positive cones, and other late-onset cellular markers such as PKCα-positive bipolar cells and Müller glial cells up to 200 days of differentiation, confirms that it is not linked to a developmental delay, but actually reflects a death of differentiated photoreceptor cells corresponding to the human RP phenotype.