Regulation of hemoglobin gene expression in the clam Lucina pectinata

The clam Lucina pectinata has three different hemoglobins (Hbs): hemoglobin I (HbI), a sulfide‐reactive protein and two oxygen‐reactive proteins, hemoglobin II (HbII) and hemoglobin III (HbIII). In order to better understand the physiological roles of these hemoproteins we evaluated their gene expression at the mRNA level by RT‐qPCR. We compared two groups of clams, one group was harvested from their natural environment and the other group of clams was phytoplankton fed in a fish tank. The Hb mRNAs expression levels were normalized to that of the 18S rRNA (18S). We also evaluated histone H3 gene expression. We found that expression of the three Hb mRNAs was highest in ctenidia tissue for both conditions, while in mantle, muscle, and visceral mass, the Hbs were expressed at much lower levels for both conditions. The expression of the Hbs decreased significantly in the clams kept in a fish tank, while the expression of the housekeeping gene, 18S, and histone H3 gene, were similar in both groups, except for the visceral mass tissue where the expression of histone H3 decreased 20‐fold. These suggests that hemoglobin gene expression may be subject to environmental control, which may include response to changes in hydrogen sulfide (H2S) and oxygen (O2) concentration as well as other factors in the conditions we tested. This research was supported by NIH grants 8G12‐MD007600 and 5R25GM088023.