A Zinc Uptake Transporter ZIP1-II Is Involved in Zinc Accumulation in the Hepatopancreas of Pacific Oyster Crassostrea gigas

The Pacific oyster Crassostrea gigas is known to have an exceptional ability to accumulate zinc, which endows it with robust resistance to pathogens and makes it an excellent source of dietary zinc. ZIP1 has been identified as an important zinc uptake protein in other species, but its role in oysters remains unclear. In the present study, a ZIP1 homologue (CgZIP1-II) of the Zrt/Irt-like protein (ZIP) family was identified in C. gigas. The mRNA transcripts of CgZIP1-II were constitutively expressed in examined tissues of C. gigas, with higher levels in the hepatopancreas and gill. After zinc exposure, the mRNA transcripts of CgZIP1-II in the hepatopancreas showed a significant decline from 12 h to 14 d, while those in the gill significantly decreased at 72 h, followed by a recovery to basal level at 7 to 14 d. Immunocytochemical analysis revealed that the CgZIP1-II protein was mainly located at the plasma membrane of oyster hemocytes. Compared to the control cells, overexpression of CgZIP1-II in the transfected HEK293 cells resulted in a 2.44-fold (p < 0.05) increase in zinc content after incubation with 100 μM zinc for 24 h. Inhibition of endogenous CgZIP1-II expression with siRNAs led to a 42% reduction in zinc content in the hepatopancreas of oysters. Similarly, in vivo blocking of CgZIP1-II with anti-CgZIP1-II antibody caused a 43% decrease in zinc content in the hepatopancreas. These results collectively indicated that CgZIP1-II functioned as a zinc uptake transporter in C. gigas and played a certain role in zinc accumulation.