Regulatory elements in the rat betaB2-crystallin promoter

The suggested common regulator of the eye lens crystallin genes is c-Maf. Maf responsive elements have been detected in a number of crystallin promoters including that of the rat betaB2-crystallin gene. The betaB2-crystallin gene is active in the post-natal lens and its mRNA reaches its maximal level in the rat lens 6 months after birth. Yet c-Maf has been reported to be present in the rat lens only up to 3 months of age. This discrepancy prompted an investigation into the role of the Maf responsive element (MARE) in the regulation of activity of the rat betaB2-crystallin promoter in rat lens fiber cells. Although betaB2 promoter activity is enhanced by c-Maf in both in vitro differentiating rat lens fiber cells and CHO cells, deletion of the betaB2 MARE, which was mapped to -143/-123, does not decrease betaB2 promoter activity in lens fiber cells. Furthermore, a dominant negative c-Maf construct did not inhibit activity of the betaB2 promoter in lens fiber cells. The data suggest that the betaB2 MARE does not play a major role in regulating activity of the betaB2 promoter. Rather, a putative Sox binding site at -164/-159 and a positive element at -14/-7 seem to be the prime regulatory elements.