Molecular Orchestration of Epithelial Mesenchymal Transition During Trophoblast and Placental Development

Abstract

In Eutherian mammals, placenta is a highly specialized extra-embryonic organ that provides the feto-maternal interface and modulates the uterine environment conducive to successful pregnancy. Placenta originates from trophectoderm cells of the blastocyst and is comprised of various lineages of trophoblast cells, endothelial and smooth muscle cells. Since trophectoderm cells are epithelial in nature, it is obvious that epithelial mesenchymal transition (EMT) is a hallmark of placentation. In this report, we aimed to identify the molecular signature that regulates EMT during trophoblast and placental development in mice. On E7.5 onwards the trophoblast stem cells located in ectoplacental cone rapidly divides, differentiate leading to formation of placenta proper. Functional EMT transcriptome in mouse implantation sites on E7.5 and E9.5 were analyzed using a RT2 profiler real time PCR array scanning 84 EMT related genes. Validation of the array was performed using real time q-PCR and western blot analyses. Array result showed that there was an overall reduction of EMT gene expression in the implantation site as gestation progressed from E7.5 to E9.5 albeit the levels of EMT gene expression were substantial on both days. The differentially expressed EMT genes were further assessed during a) placental development using mouse placental samples from various days of gestation, b) induction of either EMT or differentiation in trophoblast stem (TS) cells using western blot analysis. The genes thus identified include transcription factors (Esr1, Snai2, Stat3, Foxc2), mesenchymal markers (Vim, Fn1), extracellular matrix and cell adhesion genes (Col1a2, Col3a1, Itga5, Vcan), migration and motility genes (Msn, Fn1, Pdgfrb). Extent of EMT gene expression was highest in placenta from E12.5 of mouse gestation. In addition, ectopic administration of EMT inducer led to the induction of EMT in TS cells as evidenced by EMT gene expression profile. Furthermore, differentiation of TS cells to other trophoblast lineages led to decline in EMT gene expression. Our data thus provides new insights into the importance of EMT during trophoblast stem cell differentiation and placental morphogenesis.