OTX2 homeodomain protein binds a DNA element necessary for interphotoreceptor retinoid binding protein gene expression

Transcription of the human interphotoreceptor retinoid binding protein (IRBP) gene is strictly tissue specific, being restricted to retinal photoreceptors and pinealocytes. We have previously demonstrated that a sequence named A element, in the IRBP promoter is essential for IRBP gene transcription in vivo. Here we demonstrate that the human homeodomain protein OTX2 is present in nuclear extracts of IRBP expressing cells and specifically interacts with the IRBP A promoter element in vitro. OTX2, as well as CRX, a homeodomain protein very similar to OTX2, activates the human IRBP promoter in co-transfection experiments.