Iron metabolism and haemoglobin formation in the embryonated hen egg. 2. Some observations on the embryonic blood supply

Change of zinc mobilization and gene expression of key zinc transport proteins between the yolk sac membrane and liver of duck embryonic developing

Zinc (Zn) deposition in egg yolk is essential for the rapid growth and complete development of the avian embryo. Thus, it is crucial to obtain maximal Zn mobilization at an appropriate time during development in favor of the survival of avian embryos. The aim of this study was to study the developmental change of Zn mobilization and gene expression related to key Zn transport proteins between the yolk sac membrane and embryonic liver from the incubation d 17 (E17) to d 32 (E32) during duck embryonic developing. The weights of duck embryo, embryo without yolk sac, and embryonic liver increased as well as the yolk sac weight decreased linearly (P < 0.0001) when incubation day increased. The Zn concentration in the yolk sac did not change from E17 to E29 and only declined significantly from E29 to E32 of duck embryos, while hepatic Zn level decreased linearly as with the increased incubation time (P < 0.01). When the incubation day increased, the decreased Zn amount in the yolk sac and the increased Zn amount in the embryonic liver were observed (P < 0.0001). The calculated transfer-out rate of Zn in the yolk sac and transfer-in rate of Zn in livers were both increased from E23-26 to E29-32 (P < 0.01). Among E17, E23 and E29, the solute carrier family 39 member (ZIP) of ZIP10, ZIP13, and ZIP14 genes mRNA expressions were increased in yolk sac membrane but were decreased in the embryonic liver, while metallothionein 1 mRNA expression was increased both in the yolk sac membrane and liver (P < 0.05). In conclusion, yolk sac membrane and embryonic liver tissues displayed the similar developmental patterns of Zn mobilization and metallothionein 1 mRNA expression from E17 to E32 during duck embryonic developing. The appropriate time of the maximal rate of Zn mobilization were observed between E29 and E32 of duck embryo, associated with the significant changes of gene expression related to some key Zn transport proteins on E29 in yolk sac membrane and liver tissues.

Trace mineral metabolism in the avian embryo

Trace mineral metabolism in the developing avian embryo begins with the formation of the egg and the trace mineral stores contained within it. Vitellogenin, the yolk precursor protein, serves as a trace mineral transporting protein that mediates the transfer of these essential nutrients from stores within the liver of the hen to the ovary and developing oocyte, and hence, to the yolk of the egg. Lipovitellin and phosvitin, derived from intraoocytic proteolytic processing of vitellogenin, are also trace mineral binding proteins that form important storage sites within the granule subfraction of yolk. The mobilization and uptake of egg trace mineral stores is mediated by the extra-embryonic membranes, principally the yolk sac membrane. The yolk sac also serves as a short-term storage site for trace minerals. Because it is an important site of plasma protein synthesis, the yolk sac has the ability to regulate the export of trace minerals to the embryo during development. Within the embryo, specific metaloproteins function in the interorgan transport cellular uptake, and intracellular storage of trace minerals. Thus, embryonic trace mineral homeostasis is established through the coordinated actions of the yolk sac, which mobilizes and exports trace minerals derived from egg stores; the vitelline circulation, which transports them to the embryo; and the liver, which accumulates trace minerals and distributes them to the rest of the tissues of the embryo via the embryonic circulation.

Mechanisms of lipid peroxide formation in animal tissues

1. Homogenates of rat liver, spleen, heart and kidney form lipid peroxides when incubated in vitro and actively catalyse peroxide formation in emulsions of linoleic acid or linolenic acid. 2. In liver, catalytic activity is distributed throughout the nuclear, mitochondrial and microsomal fractions and is present in the 100000g supernatant. Activity is weak in the nuclear fraction. 3. Dilute (0.5%, w/v) homogenates catalyse peroxidation over the range pH5.0-8.0 but concentrated (5%, w/v) homogenates inhibit peroxidation and destroy peroxide if the solution is more alkaline than pH7.0. 4. Ascorbic acid increases the rate of peroxidation of unsaturated fatty acids catalysed by whole homogenates of liver, heart, kidney and spleen at pH6.0 but not at pH7.4. 5. Catalysis of peroxidation of unsaturated fatty acids by the mitochondrial and microsomal fractions of liver is inhibited by ascorbic acid at pH7.4 but the activity of the supernatant fraction is enhanced. 6. Inorganic iron or ferritin are active catalysts in the presence of ascorbic acid. 7. Lipid peroxide formation in linoleic acid or linolenic acid emulsions catalysed by tissue homogenates is partially inhibited by EDTA but stimulated by o-phenanthroline. 8. Cysteine or glutathione (1mm) inhibits peroxide formation catalysed by whole homogenates, mitochondria or haemoprotein. Inhibition increases with increase of pH.