Mineral metabolism in the developing turkey embryo—II. The role of the yolk sac

Abstract

1. 1. Turkey embryos were incubated in ovo or in long-term shell-less culture ( ex ovo) for 14, 18, 22 or 26 days, at which time the concentrations of zinc, copper, iron, manganese and calcium in yolk and yolk sac membrane were determined. 2. 2. Yolk manganese and calcium concentrations increased during incubation in ovo while the concentrations of zinc, copper and iron declined. The concentrations of zinc, copper and iron in yolk from ex ovo embryos did not decline. Yolk calcium concentration increased during incubation ex ovo, although to a much lesser extent than that observed in ovo. 3. 3. The concentration of zinc, copper and iron declined in yolk sac tissue during incubation in ovo whereas no decline was observed for yolk sac tissue from ex ovo embryos. Yolk sac calcium and manganese concentrations increased during incubation in ovo and ex ovo, although the increase in calcium concentration for ex ovo yolk sac was much smaller than that observed in ovo. 4. 4. A peak corresponding to metallothionein (MT) which bound both zinc and copper was isolated from yolk sac cytosol on day 14 of incubation in ovo using gel-permeation column chromatography. 5. 5. Further fractionation of the MT peak by anion exchange chromatography revealed three metalbinding peaks designated MT-1, MT-2a and MT-2b. The majority of the zinc was bound to MT-2a and MT-2b whereas most of the copper was bound to a single peak (MT-2b). 6. 6. The concentrations of zinc and copper in yolk sac cytosol reached a maximum on day 14 of incubation in ovo and declined through to day 28 (hatching). The majority (85%–90%) of cytosolic copper was associated with MT, whereas only 30–40% of the zinc was bound to MT.