C-MYB ACTS AS TRANSCRIPTIONAL ACTIVATOR OF THE QUAIL PAX6 (PAX-QNR) PROMOTER THROUGH 2 DIFFERENT MECHANISMS

To understand the regulation of the Pax-6 gene, which plays an importa nt role in eye development, we have characterized the promoter region of the quail Pax-6(Pax-QNR) gene. In addition to TATA and CAAT boxes, sequence analysis revealed several putative cis-regulatory elements am ong which three myb-responsive elements (MRE). C-myb encodes a nuclear , DNA-binding phosphoprotein that functions as transcriptional regulat or. Co-transfection in quail embryo cells of the Pax-QNRlpax-6 promote r with a vector expressing the 75 kDa c-myb protein resulted in an inc rease in Pax-QNR promoter activity. By footprinting experiments we ide ntified multiple binding sites for the myb protein within the promoter region. Protein containing the myb DNA-binding domain fused to the VP 16-transactivation domain was fully efficient in Pax-QNR promoter tran sactivation, demonstrating that myb can transactivate through a direct binding on DNA. However, a myb truncated protein devoid of DNA-bindin g domain was also able to transactivate the Pax-QNR promoter. These re sults show that this promoter can be transactivated by the myb protein directly as well as indirectly. Finally we show by in situ hybridizat ion that c-myb is strongly expressed in the developing neuroretina, si multaneously with Pax-QNR. These observations suggest that the c-myb p rotein may be a regulator of Pax-QNR/pax-6.