Cloning of homeobox genes involved in the differentiation of placental cells producing peptide hormones

胎盘绒毛合成胎盘催乳素（PL）和绒毛膜促性腺激素（CG）等激素。这些肽类激素对于妊娠的维持和胎儿的发育成长具有重要作用。众所周知，胎盘催乳素和垂体生长激素（GH）的基因具有序列同源性，并且源自共同的祖先基因。绒毛膜促性腺激素和垂体促性腺激素（黄体生成素=LH，卵泡刺激素=FSH）和促甲状腺激素（TSH）也源自共同的祖先基因。最近，研究表明，GH 和 TSH 的组织特异性表达受 POU 家族蛋白转录因子 Pit-1 的控制。这一发现使我们推测 POU 家族转录因子可能在胎盘激素的表达中发挥重要作用。由此研究胎盘组织是否表达属于POU家族的转录因子。为了研究 Pit-1 是否存在于人胎盘组织中，以垂体 RNA 为模板，通过逆转录聚合酶链反应 (RT-PCR) 克隆了编码人 Pit-1 的 cDNA。利用该cDNA，发现胎盘组织不表达Pit-1基因，提示其他转录因子参与了胎盘组织PL和CG的表达。通过RT-PCR寻找POU家族的表达，发现Oct-1在胎盘中表达。结果表明，Pit-1样转录因子可能存在于胎盘中，因为Oct-1与Pit-1异二聚化并增强了其作用。对其他转录因子的搜索发现，属于配对结构域蛋白的Pax-8也在胎盘中表达。我们已经证明Pax-8对于甲状腺球蛋白基因的甲状腺特异性表达发挥重要作用。结果表明 Pax-8 可能参与肽激素的胎盘特异性表达。最近的研究表明，转录因子的激活需要翻译后修饰，例如磷酸化和还原。例如，Pit-1 通过磷酸化被激活。然而，从未研究过翻译后中间化是否也是 Pax-8 激活所必需的。我们的研究表明 Pax-8 通过还原而不是通过磷酸化被激活。因此推测氧化还原调节对于胎盘基因的组织特异性表达很重要。较少的

Placental villi synthesize hormones such as plaental lactogen (PL) and chorionic gonadotropin (CG). These peptide hormones play important role for the maintenace of pregnacy and the development and growth of fetus. It is well known that the genes for placental lactogen and pituitary grwoth hormone (GH) share sequence homology and originate from a common ancestral gene. Also chorionic gonadotropin and pituitary gonadotropins (luteinizing hormone=LH and follicle stimulating hormone=FSH) and thyroid stimulating hormone (TSH) originate from a common ancestral gene. Recently, it has been shown that tissue specific expression of GH and TSH is controlled by a transcriptional factor, Pit-1, belonging to POU family protein. This finding lead us to postulate that POU family transcription factor (s) may play important role for the expression of placental hormones. It was thsu investigated whether placental tissue expresses transcription factor belonging to POU family. To study whether Pit-1 is ex … More pressed in human placental tissue or not, a cDNA coding for human Pit-1 was cloned by reverse transcription-polymerase chain reaction (RT-PCR) using pituitary RNA as a template. Using this cDNA,it was revealed that placental tissue does not express Pit-1 gene, suggesting other transcription factor is involved in the placental tissue expression of PL and CG.The search for the expression of POU family by RT-PCR revealed that Oct-1 is expressed in placenta. The result indicated that Pit-1 like transcription factor might be present in placenta since Oct-1 heterodimerizes with Pit-1 and augments its action.Search for other transciption factors revealed that Pax-8, belonging to paired domain protein is also expressed in the placenta. We have demonstrated that Pax-8 play important role for the thyroid specific expression of thyroglobulin gene. The results indicate the possible involvement of Pax-8 for the placental specific expression of peptide hormones. Recently it was demonstrated that post-translational modification such as phosphorylation and reduction is required for the activation of transcription factors. For example, Pit-1 is activated by phosphorylation. However, it has never been studied whether post-translational midification is also required for the activation of Pax-8. Our study revealed that Pax-8 is activated by reduction but not by phosphorylation. It is thus speculated that redox regulation is important for the tissue specific expression of placental genes. Less