We sought to determine whether differentiation agents such as retinoids and butyrate regulate transcript levels of interphotoreceptor retinoid binding protein (IRBP) and cone rod homeobox (CRX), a homeodomain transcription factor that regulates IRBP promoter activity. WERI-Rb1 retinoblastoma cells were treated with all-trans retinol, all-trans retinoic acid, or butyrate. IRBP and CRX mRNA levels were determined by quantitative RT-PCR. Butyrate at low concentrations increased both mRNA levels but suppressed them at higher concentrations. Retinoic acid had minimal effects. Retinol increased CRX mRNA over four fold. IRBP and CRX transcript levels are sensitive to butyrate and CRX expression is sensitive to retinol.

These in vitro assay data suggest that murine retina nuclei contain all the DNA repair factors necessary for OMGR, a finding that is prerequisite to attempting endogenous gene repair in mouse retina.

The expression of interphotoreceptor retinoid binding protein (IRBP) is limited to photoreceptor cells of the retina and pinealocytes of the pineal gland. We sought to define cis-elements of the mouse IRBP 5P P flanking region that are required for this restricted activity. In vitro transient transfections of retinoblastoma and neuroblastoma cells and in vivo experiments with transgenic Xenopus laevis indicate that 3 31783/+101 and 3 3156/ +101 IRBP gene fragments directed expression predominantly to the retina and pineal, with minor neuronal expression elsewhere. In contrast, a 3 370/+101 fragment was less restrictive in controlling expression, exhibiting activity not only in retina, but also in forebrain, hindbrain, spinal cord, and motor neurons innervating gills. ß