Author
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Richards, Mark |
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Submitted to: Trace Elements in Man and Animals (TEMA)
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/24/1996 Publication Date: N/A Citation: N/A Interpretive Summary: A variety of trace elements are required for the normal growth and development of avian embryos. Without an appropriate supply, the embryo ceases to grow properly and defects develop in virtually all of the major organs of the body. In extreme cases, the embryo dies. Similar outcomes are observed when too much of a particular trace element is given to the developing embryo. Thus, a precisely regulated supply of each required trace element is necessary for successful embryonic development and hatching of the chick. This manuscript summarizes current knowledge about the trace element content of avian eggs and it also explores the strategies employed by the developing avian embryo and its tissues to acquire and assimilate trace elements required for its development inside of the egg. The information in this report is useful in understanding the trace element requirements of the laying hen in order to ensure successful production of healthy and normal offspring. This report also offers researchers new ideas about the basic biochemical processes involved trace element metabolism during avian embryonic growth and development. Technical Abstract: Trace element metabolism during avian development begins with the formation of the egg and the trace element stores contained within it. Vitellogenin, a yolk precursor protein, serves to transport trace elements 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 the intraoocytic proteolytic processing of vitellogenin, are also trace element binding proteins that form important metal storage sites within the granule subfraction of yolk. The mobilization and uptake of egg trace element stores are mediated by the extra-embryonic membranes, principally the yolk sac membrane. The yolk sac can also serve as a short-term storage site for trace elements through its synthesis of specific metal-binding proteins like metallothionein. Because it is an important site of plasma protein synthesis (including metal-transporting proteins like albumin and transferrin), the yolk sac has the potential to regulate the export of trace elements to the embryo. Within the embryo, specific metalloproteins function in the interorgan transport, cellular uptake, and intracellular storage of trace elements. Thus, embryonic trace element homeostasis is established through the coordinated actions of the yolk sac, which mobilizes and exports trace elements derived from egg stores, the vitelline circulation, which transports them to the embryo, and the liver, which accumulates trace elements and distributes the to other tissues of the embryo via embryonic circulation. |
