QUAIL PAX-6 (PAX-QNR) MESSENGER-RNAS ARE EXPRESSED FROM 2 PROMOTERS USED DIFFERENTIALLY DURING RETINA DEVELOPMENT AND NEURONAL DIFFERENTIATION

During investigations on the regulation of the Pax-6 gene, we characte rized a cDNA from quail neuroretina showing a 5' untranslated region d istinct from that previously described and initiated from an internal promoter, Using RNase protection and primer extension mapping, we loca lized this second quail Pax-6 promoter, termed P1, As reported for the already described P0 promoter, P1 was also transactivated in vitro by the p46(pax-QNR) protein, RNase protection assays performed with quai l neuroretina RNA showed that P0-initiated mRNAs were detected before the P0-initiated mRNAs, remained constant up to embryonic day 8, and d ecreased slowly thereafter whereas, P0-initiated mRNAs accumulated up to embryonic day 8, In contrast, quail retinal pigmented epithelium ex pressed only the P1-initiated mRNAs, Transformation of these cells by the v-myc oncogene induced neuronal traits in the culture, which there after, in addition to the P1-initiated mRNAs, expressed Pax-QNR from t he P0 promoter, These results suggest that expression of the quail Pax -6 gene is under the control of different regulators through alternate promoters, P0 being activated at the onset of neuronal differentiatio n.