Developmental changes in hepatic metallothionein, zinc, and copper levels in genetically altered mice

Using mice that either overexpress metallothionein 1 (MT-1*) or do not expr ess metallothionein 1 and 2 (MT-null) and a control strain (C57BL/6), the e ssential metal storage function of hepatic metallothionein and its subcellu lar localization were investigated during development. Hepatic metallothion ein, zinc, and copper levels were measured in all groups from gestational d ay 20 to 60 days of age. Hepatic metallothionein levels were maximal during the perinatal period in both MT-1* and C57BL/6 mice with levels approximat ely three times higher in MT-1* mice. MT-null mice had no detectable hepati c metallothionein throughout development. Hepatic zinc levels were highest in the neonatal period of MT-1* and C57BL/6 mice and declined to adult leve ls by 30 days of age, while hepatic zinc levels in MT-null mice did not var y markedly throughout development. Hepatic copper profiles were very simila r in MT-1* and MT-null mice as compared with the C57BL/6 mice. Correlation analysis showed a strong positive correlation between hepatic metallothione in and zinc levels in MT-1* mice, moderate correlation between hepatic meta llothionein and metals in C57BL/6 mice, but only a very weak correlation be tween hepatic metallothionein and copper levels in MT-1* mice. Immunohistoc hemical localization showed specific nuclear staining in both MT-1* and C57 BL/6 mice during the neonatal period with a gradual shift to the cytoplasm. The results show that hepatic metallothionein is a major determinant of zi nc but not copper levels during murine development. Additionally, hepatic m etallothionein levels and localization are regulated in a similar manner in MT-1* and C57BL/6 mice. The MT-null mice maintain a basal level of zinc su fficient for development, which was found to be 15.9 mu g/g. his value was similar to the levels of hepatic zinc that was not bound to metallothionein in MT-1* and C57BL/6 mice during development.