Activation of vitellogenin gene transcription is a direct response to estrogen in Xenopus laevisliver

Estrogen induces the synthes is of vitellogenin mRNA by activating transcription of the vitellogenin genes. Quantitative inhibition of 1iver protein synthesis by cycloheximide does not prevent activation of vitellogenin gene transcription. The relative transcription rate of the vitellogenin genes in estrogen stimulated liver is similar in control and cycloheximide treated animals (800-1000ppm). Selective estrogen activation of vitellogenin gene transcription therefore represents a direct effect of estrogen on vitellogenin gene transcription which can occur without any change in the cells' protein complement. Two other cellular responses to estrogen, the induction of nuclear estrogen receptor, and an increased rate of total nuclear RNA synthesis, are blocked by cycloheximide administration. Since the overall rate of vitellogenin mRNA synthesis is a function of both the selective estrogen activation of vitellogenin gene transcription which is not blocked by cycloheximide and the increased rate of total nuclear RNA synthesis which is blocked by cycloheximide, the total rate of vitellogenin mRNA synthesis is markedly reduced following cycloheximide administration.