Synthesis of a Metallothionein-Like Protein by Developing Turkey Embryos Maintained in Long-Term, Shell-Less Culture

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Abstract
Turkey embryos were maintained in long-term, shell-less culture to the age of 17 days. At this time, 10 cultures were given saline (controls), and 10 cultures were given 30 μg zinc in saline (+ Zn). In addition, all cultures received 5 μCi each of [35S]cystine and 65Zn dissolved in the saline and applied to the chorioallantoic membrane. After a further 20 h of incubation, no significant differences were found for embryo, liver, or yolk sac weights nor for relative liver size, hematocrit, serum protein, or serum concentrations of zinc and copper for the control and + Zn cultures. The addition of zinc to the cultures significantly (p < 0.01) elevated hepatic and yolk sac cytosol 65Zn and zinc concentrations. More than 70% of the increased 65Zn and zinc in the cytosol of liver and yolk sac could be accounted for as that bound to a lowmolecular-weight metallothionein (MT)-like protein. Added zinc significantly (p < 0.01) increased the incorporation of [35S]cystine and 65Zn into the MT-like protein from liver and yolk sac indicating de novo synthesis of this protein. Liver and yolk sac MT-like proteins eluted from DEAE Sephadex A-25 columns as a single predominant species. The synthesis of an MT-like protein by liver and yolk sac suggests a role in embryonic zinc homeostasis. Moreover, shell-less culture of the avian embryo appears to be a useful method for studying zinc metabolism during periods of embryonic growth and development.

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