Regulation of the prolactin receptor gene expression and its application to improvement of animal

本实验研究了催乳素受体基因在小鼠乳腺不同生殖阶段的表达调控。为了检测催乳素受体和酪蛋白mRNA的水平，作者利用嵌合DNA和竞争DNA构建了竞争性逆转录和聚合酶链反应。本研究结果如下。（一）.催乳素受体基因的表达主要受催乳素、雌二醇和孕酮的控制。高浓度的孕酮抑制催乳素和雌二醇的增加作用。（B）。催乳素受体基因的表达发生在分娩前约8小时，是催乳作用的触发因素。孕中晚期孕酮直接抑制泌乳的开始。（c）.哺乳期第5天。催乳素受体mRNA的水平随时间的推移而降低。在断奶12小时时其水平最低，并维持低水平直到48小时。在断奶24小时时，提供寄养幼仔。催乳素受体mRNA水平在6小时内恢复到0小时断奶对照组水平。酪蛋白mRNA的变化趋势与催乳素受体mRNA的变化趋势基本一致。（d）.如（c）中所述，分别通过24小时断奶或6小时再哺乳估计催乳素受体mRNA的降解率和合成率。泌乳第1天泌乳素受体mRNA合成活跃，泌乳第10天酪蛋白合成活跃。这两种mRNA的水平变化主要与其mRNA合成速率有关。

In the present experiments, the author examined the regulation of prolactin receptor gene expression at various reproductive stages of the mouse mammary gland. In order to determine the level of prolactin receptor and casein mRNAs, the author constructed the competitive reverse-transcription and polymerase chain reaction using the chimeric and competitor DNAs. The results obtained in this study were as follow. (a). The expression of the prolactin receptor gene is controlled dominantly by prolactin, estradiol and progesterone at virgin and early pregnancy. The high concentration of progesterone inhibited the increasing action of prolactin and estradiol. (b). The expression of the prolactin receptor gene occurs about 8 hr prior to parturition and is a trigger for lactogenesis. During mid to late pregnancy, progesterone inhibited directly the initiation of lactation. (c). On day 5 of lactation. the level of prolactin receptor mRNA decreased in time-dependent manner following the removal of pups. Its level was minimal at 12 hr of weaning and low levels were maintained until of 48 hr. At 24 of weaning, foster pups were supplyed. The level of prolactin receptor mRNA returned to that of the 0 hr-weaned control within 6 hr, In case of casein mRNA,the changing profile was essentially similar to that of prolactin receptor mRNA.(d). The rates of degradation and synthesis of prolactin receptor mRNA were estimated by the 24 hr-weaning or by the 6 hr-resuckling, respectively, as described in (c). The active synthesis of prolactin receptor mRNA was found on day 1 of lactation, and that of casein synthesis was on day 10 of lactation. The levels of the two mRNAs changed primarily in relation to their rates of mRNA synthesis.