Incorporation of plasma proteins during oocyte growth and its hormonal control in winter flounder, Pseudopleuronectes americanus (Walbaum)

Bhat, Krishna Moorthi (1986) Incorporation of plasma proteins during oocyte growth and its hormonal control in winter flounder, Pseudopleuronectes americanus (Walbaum). Masters thesis, Memorial University of Newfoundland.

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Abstract

Direct evidence is provided for ovarian incorporation of plasma proteins other than vitellogenin in winter flounder Pseudopleuronectes americanus. Two major polypeptides of molecular weights 70 K and 28 K from Peak A protein(s) of the plasma were demonstrated to be incorporated into ovarian proteins. Both the polypeptides were structurally different from vitellogenin and were found to exist in the oocyte as polypeptide fragments of molecular weights 28 K, 70 K and 76 K. Vitellogenin was shown to occur as 96 K and 86 K fragments in the oocyte. The ovarian polypeptides of molecular weight 96 K fragment from vitellogenin, and 28 K fragment from Peak A protein(s) appear to be completed together and are classified here as lipovitellin 1 and lipo-vitellin II. This is similar to the molecular organization of yolk in Xenopus laevis [Berridge, M.V., and Lane, C.D. (1976). Cell, 8, 283-297]. In addition, the presence of the 70 K and 28 K polypeptides of Peak A protein(s) in the testicular proteins has been established. -- Carbohydrate-poor pituitary proteins stimulated the ovarian incorporation of vitellogenin and the non-vitellogenin plasma proteins, Peak A protein(s) and Peak E protein(s). A biologically active peptide (Rf 0.72 protein) was obtained from the carbohydrate-poor proteins; this has a molecular weight of 14.3 K by polyacrylamide gel electrophoresis containing sodium dodecyl sulphate and elutes in the region of 28 K on Ultrogel AcA 44 together with prolactin and growth hormone. A regulatory role of this gonadotropin in the ovarian uptake of Peak A protein(s) was established. These findings were in agreement with the earlier studies on the duality of gonadotropins in many species of teleosts, reported from this laboratory (see Idler and Ng, 1983).

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