Six indicator genes for zinc (Zn) homeostasis in freshwater teleost yellow catfish Pelteobagrus fulvidraco: molecular characterization, mRNA tissue expression and transcriptional changes to Zn exposure

Excessive Zn in the aquatic environment can be toxic and causes dysfunction in Zn homeostasis for fish, which ultimately influences the function of various biological processes. Zn homeostasis is controlled by Zn transporters. This study cloned and characterized the full-length cDNA sequences of six Zn transport-relevant genes (ZnT1, ZnT5, ZnT7, ZIP4, ZIP5 and MTF-1) from yellow catfish Pelteobagrus fulvidraco. The six genes share similar domains to their corresponding members of mammals. Their mRNA amounts were widely existent across eight tissues (intestine, liver, brain, heart, gill, muscle, spleen and mesenteric fat), but relatively predominant in the liver and intestine. On day 28, Zn exposure tended to increase transcript levels of ZnT1, ZnT5 and MTF-1, decrease hepatic ZIP5 expression, but did not significantly affect the expression of ZnT7 and ZIP4. On day 56, Zn exposure tended to increase transcript levels of ZnT1 and MTF-1, down-regulate hepatic mRNA amounts of ZIP4 and ZIP5; among three Zn treatments, ZnT5 expression in the 0.5 mg Zn/L group and ZnT7 expression in the 0.25 mg Zn/L group were the highest. The mRNA abundances of these genes showed Zn concentration- and exposure time-dependent manners. For the first time, we characterized the full-length cDNA sequences of six Zn transport-relevant genes in fish, explored their tissue expression profiles and transcriptional responses to Zn exposure. Our study built good basis for further investigating their physiological functions of these genes and provided new insights into the regulatory mechanisms of Zn homeostasis in fish.