Translation of hormone-induced messenger RNA in amphibian oocytes: I. Induction by estrogen of messenger RNA encoded for vitellogenic protein in the liver of the male African clawed toad (Xenopus laevis)

Abstract

Induction of the synthesis of the vitellogenic proteins, lipovitellin and phosvitin, in the liver of the male African clawed toad (Xenopus laevis) was investigated as a function of time after treatment with estradiol-17beta [1,3,5(10)-estratriene-3,17beta-diol]. The appearance of mRNAs encoded for lipovitellin and phosvitin in the cytoplasmic fraction of the liver was assayed by microinjections of hepatic mRNA preparation [either polyribosomes or poly(A)-rich RNA] into oocytes obtained from mature female toads. Oocytes were then incubated in the presence of radioactive amino acid(s) at 19 degrees for periods of time varying from 4 to 18 hr after microinjection. The results show that at 2 hr after hormone treatment more mRNA was present in the cytoplasm, and that from 2 to 72 hr after treatment the level of induced mRNA increased almost linearly to 110% above the control values. Experiments employing specific lipovitellin antiserum indicated no radioactive lipovitellin among the proteins synthesized in oocytes microinjected with hepatic mRNAs isolated from 3 to 9 hr after hormone treatment. However, a marked synthesis of immunoprecipitable, radioactive lipovitellin and an enhanced incorporation of [3H]serine occurred in the oocytes microinjected with hepatic mRNA preparations obtained from toads treated with hormone for 12 or more hr. The identities of the proteins encoded by the mRNAs induced early in estrogen action (2-9 hr) in the male amphibian liver are unknown. It is surmised that some of these proteins may function in the regulation of the subsequent synthesis of the vitellogenic proteins.