Molecular Cloning and Characterization of the 5′-Flanking Regulatory Region of the Carbonic Anhydrase Nacrein Gene of the Pearl Oyster Pinctada fucata and Its Expression

The carbonic anhydrase nacrein participates in the formation of the nacreous or prismatic layer of Pinctada fucata. We isolated a genomic clone containing the nacrein gene and cloned the 5′-flanking region. Within the 1336 bp 5′ flanking region, we identified putative cis-acting elements, including the TATA box (TATAAAA) at −82 bp, and AP1 (−819 bp) and Oct-1 (−1244 bp) binding sites. In addition to the mantle, the nacrein gene is also expressed in the adductor muscle, liver, and foot. These results showed that nacrein not only takes part in the formation of the hard tissue but also might be involved in acid–base balance, ion transport, and maintenance of ionic concentration. In vitro transcription experiments showed that the addition of human c-jun activates transcription from the nacrein promoter. This is the first report of a promoter from a gene that controls the formation of the hard tissue of mollusk shells.