Dataset for: Carbonic Anhydrase 2-like in the giant clam, <i>Tridacna squamosa</i>: characterization, localization, response to light, and possible role in the transport of inorganic carbon from the host to its symbionts

The fluted giant clam, <i>Tridacna squamosa</i>, lives in symbiosis with zooxanthellae which reside extracellularly inside a tubular system. Zooxanthellae fix inorganic carbon (C<sub>i</sub>) during insolation and donate photosynthate to the host. Carbonic anhydrases catalyze the interconversion of CO<sub>2</sub> and HCO<sub>3</sub><sup>-</sup>, of which carbonic anhydrase 2 (CA2) is the most ubiquitous and involved in many biological processes. This study aimed to clone a <i>CA2</i> homolog (<i>CA2-like</i>) from the fleshy and colorful outer mantle as well as the thin and whitish inner mantle of <i>T. squamosa</i>, to determine its cellular and subcellular localization, and to examine the effects of light exposure on its gene and protein expression levels. The cDNA coding sequence of <i>CA2-like</i> from <i>T. squamosa</i> comprised 789 bp, encoding 263 amino acids with an estimated molecular mass of 29.6 kDa. A phenogramic analysis of the deduced CA2-like sequence denoted an animal origin. CA2-like was not detectable in the shell-facing epithelium of the inner mantle adjacent to the extrapallial fluid. Hence, CA2-like is unlikely to participate directly in light-enhanced calcification. By contrast, the outer mantle, which contains the highest density of tertiary tubules and zooxanthellae, displayed high level of <i>CA2-like</i> expression, and CA2-like was localized to the tubule epithelial cells. More importantly, exposure to light induced significant increases in the protein abundance of CA2-like in the outer mantle. Hence, CA2-like could probably take part in the increased supply of inorganic carbon (C<sub>i</sub>) from the host clam to the symbiotic zooxanthellae when the latter conduct photosynthesis to fix C<sub>i</sub> during light exposure.