Regulation of Protein Synthesis in Chick Oviduct

Egg white protein synthesis is induced and maintained in oviduct magnum of immature female chicks by administering gonadal steroid hormones. The relative rate of synthesis of four egg white proteins (ovalbumin, conalbumin, ovomucoid, and lysozyme) was measured by culturing magnum explants with radioactive amino acids followed by specific immunoprecipitation of each of the egg white proteins. Induction of these proteins was studied as a function of time, hormonal dose, and hormonal combination. A combination of estrogen, progesterone, and testosterone was found which would induce the relative rate of synthesis of each of the four egg white proteins to a level that closely approximates that observed in laying hens; this combination also promotes maximal magnum growth. The synthesis of these proteins is not strictly coordinated, since the rate of synthesis of one or more of these proteins can change relative to the others, although they are all synthesized in the same cell. Noncoordinate protein synthesis is exemplified by the changing ratio of conalbumin to ovalbumin synthesis during both primary and secondary stimulation with estrogen. The ratio of synthesis of these two proteins also changes as a function of the dosage of hormone administered. Furthermore, different combinations of hormones can produce noncoordinate synthesis; for example, the synthesis of ovomucoid and conalbumin is increased relative to ovalbumin when either progesterone or testosterone are administered along with estrogen. The most likely explanation for the change in the ratio of ovalbumin to conalbumin synthesis observed during hormonal stimulation is the 2-fold difference in the rates of degradation of their mRNAs. In contrast, changes in mRNA synthesis or activation best account for the preferential induction of conalbumin synthesis by low doses of estrogen, and the increased rates of conalbumin and ovomucoid synthesis which are produced by supplementing estrogen with either progesterone or testosterone. The results suggest that a single regulatory site for the control of egg white synthesis is unlikely since several of these proteins appear to be under independent control.