Developmental and estrogen regulation of Xenopus laevis retinol-binding protein gene expression
Gould, Lisa Jeanne
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Permalink
https://hdl.handle.net/2142/21628
Description
Title
Developmental and estrogen regulation of Xenopus laevis retinol-binding protein gene expression
Author(s)
Gould, Lisa Jeanne
Issue Date
1989
Doctoral Committee Chair(s)
Shapiro, David J.
Department of Study
Biochemistry
Discipline
Biochemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Language
eng
Abstract
The developmental regulation of the estrogen-regulated serum retinol-binding protein and estrogen receptor genes in Xenopus embryonic livers has been examined. Serum retinol binding protein (RBP) mRNA is detected exclusively in liver tissue in both adult Xenopus laevis and in tadpoles. RBP mRNA is absent in Xenopus oocytes and is present at extremely low levels in early embryos. The developmental activation of constitutive RBP gene expression parallels liver differentiation. In contrast, the capacity for estrogen induction of RBP gene transcription appears much later and is coordinate with the expression of the estrogen receptor (xER) gene. xER mRNA is expressed at extremely low levels up to stage 66, at which time there is a dramatic increase in constitutive expression and inducible expression becomes apparent for the first time. The constitutive level of hepatic xER mRNA at the completion of metamorphosis is approximately half the level in livers of uninduced adult male Xenopus, but is still sufficient for the acquisition of estrogen inducibility.
We have further examined the estrogen regulation of RBP mRNA in adult Xenopus. In vivo, the induction appears to occur primarily at the level of transcription. Although there may be other post-transcriptional mechanisms involved in the fine-tuning of this response, estrogen stimulation does not cause stabilization of the RBP message. This study demonstrates that the fold induction of RBP mRNA in primary Xenopus liver cultures is much greater than in vivo. In the liver culture system, estrogen induces the cytoplasmic level of RBP mRNA 20-30 fold, yet the rate of transcription only increases 2-3 fold and RBP mRNA stability is not altered. Northern blot analysis revealed a possible defect in the processing of RBP mRNA precursors which is partially corrected upon estrogen administration. This would account for both the reduced level of constitutive expression and the large induction of RBP mRNA observed in the culture system. We propose that this defect is the result of a stress response which occurs during preparation of the liver cultures.
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