CRX and retinitis pigmentosa 1: At that time, the mRNA levels of photoreceptor markers, rhodopsin (Figure 3C), and crx, a transcription factor upstream of rhodopsin (Figure 3D), were at significantly higher levels in the retina of PBA-treated P23H RP models, indicating that PBA treatment retained visual pigment expression in the rod photoreceptor cells compared with vehicle treatment.