Developmental regulation of metallothionein mRNA, zinc and copper levels in rainbow trout, Salmo gairdneri

The metallothionein (MT) gene expression profile was followed in rainbow trout during early embryo development and in liver and gonads during the period of sexual maturation. The hepatic MT mRNA levels increase at the end of sexual maturation in both male and female rainbow trout. Although both isoforms of MT mRNA accumulate in the liver, there is a preferential increase in MT-A in the female liver. Concomitantly with this increase in MT there is a redistribution of zinc and copper to MT. In the juvenile female there is an abundance of MT mRNA in the ovaries. This is correlated to high levels of zinc in the MT fraction upon Sephadex G-75 chromatography. During ovary development the MT mRNA levels and the MT-bound zinc levels drop, with an increase in zinc being bound to high-molecular-mass proteins. At ovulation most of the zinc is found in the membrane portion upon centrifugation. In contrast to the ovaries, there are no apparent changes in either trace metal distribution or MT mRNA levels during testis development. In the developing embryo there is an increase in MT-bound copper at gastrulation. This is accompanied by an increase in both isoforms of MT mRNA. At hatch both the copper and zinc levels increase in the MT fraction, with a concomitant increase in mainly MT-A mRNA. These findings indicate that the variations in MT mRNA levels during development are closely associated with metal regulation.