Induction of ovalbumin mRNA by estrogen in the chick oviduct.

Abstract To study the induction of mRNA ov in chick oviduct tissue, two experimental designs were developed: oviduct tissue incubated in vitro with hormone, and an in vivo system involving hormone injection into the lumen of anesthetized chicks. The magnitude of hormone response in oviduct tissue suspension was shown to depend on the conditions of the incubation medium and on the previous hormonal treatment of the chicken. When animals were withdrawn from estrogen treatment (48–72 h), restimulation of oviduct minces with 10 −8 M estradiol in vitro induced-rapidly the synthesis of mRNA ov . The rate of synthesis reached its peak in the first two hours of incubation, when approximately 0.2% of the mass of the newly synthesized RNA was mRNA ov . A marked decrease in the level of mRNA ov synthesis and a gradual appearance of a lag period was observed when the estrogen withdrawal time was extended beyond 86 h. A nuclear precursor to ovalbumin mRNA could be shown to be processed into mature mRNA ov in this oviduct tissue suspension system. In vivo experiments were performed in chickens after various intervals of time following hormone withdrawal (2–13 days). Estradiol (10 −8 M) was injected into the oviduct lumen of anesthetized chicks. Within two hours a nearly maximal rate of mRNA ov synthesis was observed. These two systems have proven to be efficient for the assay of the estrogen-mediated induction of mRNA ov synthesis and serve to support the hypothesis that in the chick oviduct system, estrogen regulation of gene expression is primarily at the transcriptional level.