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

Abstract

SummaryTurkey 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.