Breton C, Di Scala-Guenot D, Zingg H H
Laboratory of Molecular Endocrinology, McGill University Health Centre, Montreal, Quebec H3A 1A1, Canada.
J Mol Endocrinol. 2001 Oct;27(2):175-89. doi: 10.1677/jme.0.0270175.
The differential, tissue-specific regulation of oxytocin (OT) binding sites allows the neurohypophysial nonapeptide OT to fulfill a dual role: to induce uterine contractions at parturition and to mediate milk ejection during lactation. Whereas uterine OT binding sites are up-regulated prior to parturition and are rapidly down-regulated thereafter, mammary gland OT binding sites gradually increase throughout gestation and remain up-regulated during the ensuing lactation period. Here, we structurally characterized OT receptor (OTR) mRNA in mammary gland and analyzed its expression during gestation and lactation and in response to steroid treatment. In mammary gland tissues, we found a 6.7 and a 5.4 kb OTR mRNA species, and both species were further analyzed by RACE (rapid amplification of cDNA ends). The 6.7 kb mRNA was found to be common to mammary gland and uterus and to extend 618 nucleotides beyond the published sequence of the rat OTR gene. The 5.4 kb mRNA species is unique to the mammary gland and terminates at a mammary gland-specific polyadenylation site that is not preceded by a classical polyadenylation signal. RT-PCR analysis did not provide any evidence for differences in the coding regions, suggesting that both uterine and mammary gland OTR mRNAs encode the same receptor protein. Furthermore, primer extension experiments showed that no differences exist in the specific transcriptional initiation sites of the OTR gene in the two tissues. During pregnancy, OTR mRNA per mammary gland increased approximately 150-fold and remained high during lactation, consistent with the previously identified regulation of OT binding sites and the role of OT during lactation. Whereas estrogen administration strongly induced the uterine OTR mRNA levels (>5-fold), mammary gland remained unaffected by steroid treatment. Moreover, tamoxifen had no effect on the mammary gland OTR mRNA level. In summary, our data demonstrate a differential control of OTR expression in uterus versus mammary gland and a mammary gland-specific OTR mRNA polyadenylation site. However, this differential control apparently does not involve the expression of different receptor genes nor the utilization of tissue-specific transcriptional initiation sites.
催产素（OT）结合位点的差异性、组织特异性调节使得神经垂体九肽OT能够发挥双重作用：在分娩时诱导子宫收缩，以及在哺乳期介导乳汁排出。子宫OT结合位点在分娩前上调，之后迅速下调，而乳腺OT结合位点在整个妊娠期逐渐增加，并在随后的哺乳期保持上调。在此，我们对乳腺中的OT受体（OTR）mRNA进行了结构表征，并分析了其在妊娠和哺乳期以及对类固醇处理的反应中的表达情况。在乳腺组织中，我们发现了6.7 kb和5.4 kb的OTR mRNA种类，并通过cDNA末端快速扩增（RACE）对这两种种类进行了进一步分析。发现6.7 kb的mRNA在乳腺和子宫中都有，并且比已发表的大鼠OTR基因序列多延伸了618个核苷酸。5.4 kb的mRNA种类是乳腺特有的，终止于一个乳腺特异性的聚腺苷酸化位点，该位点之前没有经典的聚腺苷酸化信号。逆转录聚合酶链反应（RT-PCR）分析没有提供编码区存在差异的任何证据，这表明子宫和乳腺的OTR mRNA编码的是相同的受体蛋白。此外，引物延伸实验表明，这两种组织中OTR基因的特异性转录起始位点没有差异。在怀孕期间，每个乳腺的OTR mRNA增加了约150倍，并在哺乳期保持高水平，这与之前确定的OT结合位点的调节以及OT在哺乳期的作用一致。虽然给予雌激素强烈诱导子宫OTR mRNA水平（>5倍），但乳腺不受类固醇处理的影响。此外，他莫昔芬对乳腺OTR mRNA水平没有影响。总之，我们的数据表明子宫和乳腺中OTR表达的差异性控制以及一个乳腺特异性的OTR mRNA聚腺苷酸化位点。然而，这种差异性控制显然不涉及不同受体基因的表达，也不涉及组织特异性转录起始位点的利用。
