Study on regulation of placental functions : Involvement of ovarian factors in the mechanism.

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The placenta plays an essential role in fetal growth and survival. maintenance of maternal metabolic status during pregnancy by virtue of its multiple functions relating to the transport of nutrients and waste between mother and tetus, moduiating of the matemal and fetal immune systems to prevent rejection of each other, and its endocrine function of maintaining the pregnancy. Successful development of errbryo is totally dependent on placental function. Considering these multiple functions, not only functions that are required constantly but also pregnancy stage specific events such as placental lactogen synthesis, the placenta is thought to express an abundance of biologically active molecules. In the series of experiments, we have analyzed and identified the almost 800 proteins which are stage-specifically expressed on the placental plasma membrane of the rat placenta. We have also cloned the cDNAs encoding novel prolactin (PPL) like molecules, PL-lm and PLP-D,in the rat placenta. PL-lm RNA is specitically expressed at mid-pregnancy, and PLP-D is specific to late pregnancy. In addition to these placental PPL-like molecules, we found GD3 and GM3 as the main gangliosides in the placenta. The composition changes stage specific manner in the rat placenta. Using prolonged pregnancy models and the various stage-specific indexes as mentioned above, it became clear that the stage-specific functions of placenta are controlled by matemal ovarian factors. Expression of these stage-specific functions of the placenta is related to the differentiation of trophoblasts and changes in the cellular composition. Furthermore, we got the evidence indicating that methylation of DNA of CpG islands or in the promoter regions is involved in the placental specific gene-expression and differentiation of the placenta.