Sufficient cytotrophoblast (CT) invasion into the uterine wall and subsequent remodeling of maternal uterine vasculature is critical to establish uteroplacental circulation. The production of vascular endothelial growth factor (VEGF) family molecules is confirmed in placental cells including CTs, but it is not elucidated how the VEGF system in CTs is controlled by oxygen tension and how it is involved in the development of placental circulation. To address this, we explored the effect of oxygen tension on the expression of VEGF, placenta growth factor (PlGF), and their antagonist, soluble fms-like tyrosine kinase-1 (sFlt-1) using ELISA and real-time PCR in a primary CT cell culture. For comparison, the same was conducted in parallel using other cells comprising placenta, such as human umbilical vein endothelial cells (HUVECs) and villous fibroblasts (VFs). Reduced oxygen resulted in a pronounced increase in sFlt-1 mRNA amount and sFlt-1 release into the culture media in CTs, whereas this was not the case with HUVECs and VFs. Free (not bound to sFlt-1) VEGF was not detected in CT culture media regardless of oxygen concentration, even though VEGF expression was stimulated by reduced oxygen in CTs, which was similar to the stimulation in HUVECs and VFs. Free PlGF was also diminished in CT culture media by reduced oxygen. These results implicate that CTs possess a unique property to enhance sFlt-1 production under reduced oxygen, which could consequently antagonize angiogenic activity of VEGF and PlGF. The presented findings might provide a framework with which to understand the mechanism of uterine vascular remodeling and its perturbations as exemplified in preeclampsia.
The DNA methyltransferase-like protein Dnmt3L is necessary for the establishment of genomic imprints in oogenesis and for normal spermatogenesis (Bourc'his et al., 2001; Hata et al., 2002). Also, a paternally imprinted gene, H19, loses DNA methylation in Dnmt3L-/- spermatogonia (Bourc'his and Bestor, 2004; Kaneda et al., 2004). To determine the reason for the impaired spermatogenesis in the Dnmt3L-/- testes, we have carried out a series of histological and molecular studies. We show here that Dnmt3L-/- germ cells were arrested and died around the early meiotic stage. A microarray-based gene expression-profiling analysis revealed that various gonad-specific and/or sex-chromosome-linked genes were downregulated in the Dnmt3L-/- testes. In contrast, expression of retrovirus-like intracisternal A-particle (IAP) sequences was upregulated; consistent with this observation, a specific IAP copy showed complete loss of DNA methylation. These findings indicate that Dnmt3L regulates germ cell-specific gene expression and IAP suppression, which are critical for male germ cell proliferation and meiosis.
DNA methylation of the genome is essential for mammalian development and plays crucial roles in a variety of biological processes including genomic imprinting. Although the DNA methyltransferase 3-like (Dnmt3L) protein lacks DNA methylase activity, it is thought to establish the maternal imprint in combination with the functional DNA methyltransferases. Oogenesis apparently proceeds normally in female mice homozygous for a targeted deletion of Dnmt3L, but their heterozygous offspring (Dnmt3L(mat-/-)) die before midgestation due to an imprinting defect. In this study, we show that Dnmt3L is required for the establishment of maternal methylation imprints both in the embryos and the placentae and that the placentae of these embryos develop abnormally. There is a defect in the formation of the labyrinth, reduced formation of the spongiotrophoblast layer, excess trophoblast giant cells and insufficient attachment between the chorion layer and the ectoplacental cone. In addition, we demonstrate arrest of proliferation of the extraembryonic tissue without apoptosis in vivo and a disturbance of the cell fate of Dnmt3L(mat-/-) trophoblastic stem cells in vitro. Furthermore, we report that DNA methylation during oogenesis is essential for the establishment of imprinting Mash2. These findings provide evidence that not only is DNA methylation required for the appropriate maternal imprint in the placenta but that the appropriate imprint is absolutely required for vertebrate placentation.
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