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  • Title: Estrogen downregulation of albumin and a 170-kDa serum protein in the turtle, Trachemys scripta.
    Author: Selcer KW, Palmer BD.
    Journal: Gen Comp Endocrinol; 1995 Mar; 97(3):340-52. PubMed ID: 7789749.
    Abstract:
    We examined changes in serum protein composition after estradiol-17 beta treatment of ovariectomized female Trachemys scripta, with the objective of identifying proteins that are repressed by estrogen. The experimental protocol was validated by measuring serum estradiol-17 beta levels with a specific radioimmunoassay. Control turtle sera contained little or no estradiol-17 beta (mean = 25.8 pg/ml) while estrogen-treated turtle sera had elevated estradiol-17 beta levels (mean = 333.3 pg/ml). Estrogen treatment resulted in a significant increase in serum protein concentration. The increase was due largely to a 213-kDa protein that was abundant in estrogen-treated animal sera but was low or absent in control animal sera. This protein was identified as vitellogenin based on its biochemical characteristics (molecular weight, elution profile from DEAE, precipitation in the presence of Mg2+/EDTA). Several proteins were decreased in the sera of estrogen-treated animals. One of these had a molecular weight of 66 kDa and was determined to be serum albumin. This protein crossreacted in Western blot analyses with polyclonal antisera against chicken and human serum albumins. Also, amino acid sequence analysis revealed substantial homology between the 66-kDa turtle protein and serum albumins from other vertebrate species. Another protein decreased by estrogen treatment had a molecular weight of 170 kDa. Both albumin and the 170-kDa protein were reduced in estrogen-treated turtles to levels about 50% of those present in control turtles. Using [35S]methionine-labeling and denaturing (SDS) polyacrylamide gel electrophoresis, we detected the presence of newly labeled albumin and the 170-kDa protein in T. scripta liver cube cultures, indicating that these proteins are derived from the liver. Data from this study reveal that estrogen downregulates several serum proteins in T. scripta, while upregulating serum vitellogenin. The response to estrogen in this reptile is similar to that in the amphibian Xenopus laevis, suggesting that estrogen downregulation of serum proteins during vitellogenesis may be widespread among oviparous vertebrates.
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