Abstract
Glucocorticoids induce ovalbumin and conalbumin mRNA in oviducts from chicks withdrawn from prior estrogen treatment. The magnitude and the kinetics of the responses obtained, either in vivo or in vitro, are comparable to those obtained with estrogen or progesterone. With cultured oviducts, 1 nM dexamethasone is sufficient for half-maximal accumulation of nuclear receptors and partial induction of both mRNAs, while maximal levels of receptors and both mRNAs are achieved with 30 to 100 nM dexamethasone. Competition experiments show that dexamethasone acts by binding to a class of high affinity receptors distinct from the sex steroid receptors. Dexamethasone acts synergistically with estrogen, but not with progesterone.
Highlights
The role of steroids in the inductionof specific proteins has been widely studied in eukaryoticsystems as a means of elucidating the mechanisms regulating gene expression
We have shown that ovalbumin and conalbumin synthesis can be induced in uiuo at rates comparable to those obtained with estrogens and progestins
Dose Response Relationships-The dose response for dexamethasone in culture was examined by incubating oviduct tissue fragments with ['Hldexamethasone at concentrations incubated in culture with vH]dexamethasone at the concentrations indicated using the standard conditions described under "Experimental Procedures." At 1 h, tissue samples were removed for the measurement of nuclear dexamethasone receptor levels (MN) on
Summary
Administration of estrogen to immature chicks (primary stimulation) resultsin the proliferation and differentiation of the tubular gland cells of the oviduct magnum; these cells synthesize and secreteall the majoregg white proteins including ovalbumin and conalbumin. We have shown that ovalbumin and conalbumin synthesis can be induced in uiuo at rates comparable to those obtained with estrogens and progestins For many of these studieswe have used the syntheticglucocorticoid, dexamethasone, because ithas a higher affmityfor cellular receptors, it ismetabolized more slowly, and it binds less avidly to serum proteins (such as transcortin) than all natural glucocorticoids. Tris-Cl (pH 7.5), m~ MgCI2, 1% Triton X-100, 1%sodium deoxycholate, and centrifuged at 105,000 X g for 60 min The ratesof both ovalbumin and conalbumin synthesis were measured with specific antibodies [9] and expressed as a percentage of total protein synthesis.
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