Cochrane A W, Deeley R G
Department of Biochemistry, Queen's University, Kingston, Ontario, Canada.
J Mol Biol. 1988 Oct 5;203(3):555-67. doi: 10.1016/0022-2836(88)90192-1.
Administration of estrogen to egg-laying vertebrates activates unscheduled, hepatic expression of major, egg-yolk protein genes in immature animals and mature males. Two avian yolk protein genes, encoding very low density apolipoprotein II (apoVLDLII) and vitellogenin II, are dormant prior to stimulation with estrogen, but within three days their cognate mRNAs accumulate to become two of the most abundant species in the liver. Accumulation of these mRNAs has been attributed to both induction of transcription and selective, estrogen-dependent mRNA stabilization. We have detected alterations in the size of apoVLDLII mRNA that occur during the first 24 hours that are attributable to a shift in the extent of polyadenylation as steady-state is approached. In vitro transcription assays indicate that primary activation of both genes takes place relatively slowly and that maximal rates of mRNA accumulation occur when the apoVLDLII and vitellogenin II genes are expressed at only 30% and 10% of their fully induced levels, respectively. Transcription data combined with the structural alteration of apoVLDLII mRNA suggest that stability of the two mRNAs may change as steady-state is approached. We have assessed the compatibility of this suggestion with earlier estimates of the kinetics of accumulation of both mRNAs by developing a generally useful algorithm that predicts approach to steady-state kinetics under conditions where both the rate of synthesis and mRNA stability change throughout the accumulation phase of the response. The results predict that the stability of both mRNAs decreases by at least two- to threefold during the approach to steady-state and that, although an additional destabilization of apoVLDLII mRNA may occur following withdrawal of estrogen, the steady-state stability of vitellogenin mRNA is not significantly decreased upon removal of hormone.
给产卵脊椎动物施用雌激素会激活未成熟动物和成年雄性动物肝脏中主要卵黄蛋白基因的非程序性表达。两种禽卵黄蛋白基因，编码极低密度载脂蛋白II（apoVLDLII）和卵黄生成素II，在受到雌激素刺激之前处于休眠状态，但在三天内它们的同源mRNA积累，成为肝脏中最丰富的两种mRNA。这些mRNA的积累归因于转录的诱导和选择性的、雌激素依赖性的mRNA稳定化。我们检测到apoVLDLII mRNA大小在最初24小时内发生了变化，这归因于接近稳态时多聚腺苷酸化程度的改变。体外转录分析表明，这两个基因的初始激活相对较慢，当apoVLDLII和卵黄生成素II基因分别仅以其完全诱导水平的30%和10%表达时，mRNA积累达到最大速率。转录数据与apoVLDLII mRNA的结构改变相结合表明，随着接近稳态，这两种mRNA的稳定性可能会发生变化。我们通过开发一种通用算法评估了这一建议与早期对两种mRNA积累动力学估计的兼容性，该算法预测了在整个反应积累阶段合成速率和mRNA稳定性都发生变化的条件下接近稳态动力学的情况。结果预测，在接近稳态的过程中，两种mRNA的稳定性至少降低两到三倍，并且，虽然在撤除雌激素后apoVLDLII mRNA可能会发生额外的不稳定，但去除激素后卵黄生成素mRNA的稳态稳定性并没有显著降低。
