Spatiotemporal coordination of trophoblast and allantoic Rbpj signaling directs normal placental morphogenesis

Origin and flow-mediated remodeling of the murine and human extraembryonic circulation systems

The transduction of mechanical stimuli produced by blood flow is an important regulator of vascular development. The vitelline and umbilico-placental circulations are extraembryonic vascular systems that are required for proper embryonic development in mammalian embryos. The morphogenesis of the extraembryonic vasculature and the cardiovascular system of the embryo are hemodynamically and molecularly connected. Here we provide an overview of the establishment of the murine and human vitelline and umbilico-placental vascular systems and how blood flow influences various steps in their development. A deeper comprehension of extraembryonic vessel development may aid the establishment of stem-cell based embryo models and provide novel insights to understanding pregnancy complications related to the umbilical cord and placenta.

Maternal RNA transcription in Dlk1-Dio3 domain is critical for proper development of the mouse placental vasculature

The placenta is a unique organ for ensuring normal embryonic growth in the uterine. Here, we found that maternal RNA transcription in Dlk1-Dio3 imprinted domain is essential for placentation. PolyA signals were inserted into Gtl2 to establish a mouse model to prevent the expression of maternal RNAs in the domain. The maternal allele knock-in (MKI) and homozygous (HOMO) placentas showed an expanded junctional zone, reduced labyrinth and poor vasculature impacting both fetal and maternal blood spaces. The MKI and HOMO models displayed dysregulated gene expression in the Dlk1-Dio3 domain. In situ hybridization detected Dlk1, Gtl2, Rtl1, miR-127 and Rian dysregulated in the labyrinth vasculature. MKI and HOMO induced Dlk1 to lose imprinting, and DNA methylation changes of IG-DMR and Gtl2-DMR, leading to abnormal gene expression, while the above changes didn't occur in paternal allele knock-in placentas. These findings demonstrate that maternal RNAs in the Dlk1-Dio3 domain are involved in placental vasculature, regulating gene expression, imprinting status and DNA methylation.

Chromatin remodeling of prostaglandin signaling in smooth muscle enables mouse embryo passage through the female reproductive tract

Early mammalian development occurs during embryo transit of the female reproductive tract. Transport is orchestrated by secreted oviduct fluid, unidirectional beating of epithelial cilia, and smooth muscle contractions. Using gene-edited mice, we document that conditional disruption of a component of the SWI/SNF chromatin remodeling complex in smooth muscle cells prevents transport through the oviduct without perturbing embryogenesis. Analysis with RNA sequencing (RNA-seq), transposase-accessible chromatin with sequencing (ATAC-seq), chromatin immunocleavage sequencing (ChIC-seq), and pharmacologic rescue experiments implicated prostaglandin signaling pathways. In comparison with controls, gene-edited mice had compromised chromatin accessibility at enhancer/promoters of Ptgs2, Pla2g16, Pla2r1, and Ptger3 (EP3) as well as decreased enhancer-promoter interactive looping critical for Ptgs2 (aka Cox-2) expression in a SWI/SNF complex-dependent manner. Treatment of wild-type mice with prostaglandin inhibitors phenocopied the genetically induced defect.

Variable Cre Recombination Efficiency in Placentas of Cyp19-Cre ROSAmT/mG Transgenic Mice

The aromatase-Cre recombinase (Cyp19-Cre) transgenic mouse model has been extensively used for placenta-specific gene inactivation. In a pilot study, we observed unexpected phenotypes using this mouse strain, which prompted an extensive characterization of Cyp19-Cre placental phenotypes using ROSAmT/mG transgenic reporter mice. The two strains were mated to generate bi-transgenic Cyp19-Cre;ROSAmT/mG mice following a standard transgenic breeding scheme, and placental and fetal tissues were analyzed on embryonic day 17.5. Both maternal and paternal Cre inheritance were analyzed by mating the respective Cyp19-Cre and ROSAmT/mG males and females. The genotype results showed the expected percentage of Cyp19-Cre;ROSAmT/mG fetuses (73%) and Cre mRNA was expressed in all of the Cyp19-Cre placentas. However, surprisingly, only about 50% of the Cyp19-Cre;ROSAmT/mG placentas showed Cre-mediated recombinase activity as demonstrated by placental enhanced green fluorescent protein (EGFP) expression. Further genetic excision analysis of the placentas revealed consistent results showing the absence of excision of the tdTomato in all of the Cyp19-Cre;ROSAmT/mG placentas lacking EGFP expression. Moreover, among the EGFP-expressing placentas, there was wide variability in recombination efficiency, even in placentas from the same litter, leading to a mosaic pattern of EGFP expression in different zones and cell types of the placentas. In addition, we observed a significantly higher percentage of Cre recombination activity in placentas with maternal Cre inheritance. Our results show frequent mosaicism, inconsistent recombination activity, and parent-of-origin effects in placentas from Cyp19-Cre;ROSAmT/mG mice, suggesting that tail-biopsy genotype results may not necessarily indicate the excision of floxed genes in Cyp19-Cre positive placentas. Thus, placenta-specific mutagenesis studies using the Cyp19-Cre model require extensive characterization and careful interpretation of the placental phenotypes for each floxed allele.

Notch signaling in reproduction

The Notch signaling pathway is conserved among mammalian species and controls proliferation, differentiation, and cell death in many organs throughout the body including the reproductive tract. Notch signaling plays critical roles in the development and function of both the male and female reproductive systems. Specifically, within the female reproductive tract, Notch signaling is hormone regulated and mediates key reproductive events important for ovarian and uterine function. In this review, we highlight the tissues that express Notch receptors, ligands, and downstream effectors and distinguish how these molecules regulate reproductive function in male and female mice, non-human primates, and humans. Finally, we describe some of the aberrations in Notch signaling in female reproductive pathologies and identify opportunities for future investigation.

Mapping cis-regulatory elements in the midgestation mouse placenta

The placenta is a temporary organ that provides the developing fetus with nutrients, oxygen, and protection in utero. Defects in its development, which may be caused by misregulated gene expression, can lead to devastating outcomes for the mother and fetus. In mouse, placental defects during midgestation commonly lead to embryonic lethality. However, the regulatory mechanisms controlling expression of genes during this period have not been thoroughly investigated. Therefore, we generated and analyzed ChIP-seq data for multiple histone modifications known to mark cis-regulatory regions. We annotated active and poised promoters and enhancers, as well as regions generally associated with repressed gene expression. We found that poised promoters were associated with neuronal development genes, while active promoters were largely associated with housekeeping genes. Active and poised enhancers were associated with placental development genes, though only active enhancers were associated with genes that have placenta-specific expression. Motif analysis within active enhancers identified a large network of transcription factors, including those that have not been previously studied in the placenta and are candidates for future studies. The data generated and genomic regions annotated provide researchers with a foundation for future studies, aimed at understanding how specific genes in the midgestation mouse placenta are regulated.

Implications for preeclampsia: hypoxia-induced Notch promotes trophoblast migration

In the first trimester of human pregnancy, low oxygen tension or hypoxia is essential for proper placentation and placenta function. Low oxygen levels and activation of signaling pathways have been implicated as critical mediators in the promotion of trophoblast differentiation, migration, and invasion with inappropriate changes in oxygen tension and aberrant Notch signaling both individually reported as causative to abnormal placentation. Despite crosstalk between hypoxia and Notch signaling in multiple cell types, the relationship between hypoxia and Notch in first trimester trophoblast function is not understood. To determine how a low oxygen environment impacts Notch signaling and cellular motility, we utilized the human first trimester trophoblast cell line, HTR-8/SVneo. Gene set enrichment and ontology analyses identified pathways involved in angiogenesis, Notch and cellular migration as upregulated in HTR-8/SVneo cells exposed to hypoxic conditions. DAPT, a γ-secretase inhibitor that inhibits Notch activation, was used to interrogate the crosstalk between Notch and hypoxia pathways in HTR-8/SVneo cells. We found that hypoxia requires Notch activation to mediate HTR-8/SVneo cell migration, but not invasion. To determine if our in vitro findings were associated with preeclampsia, we analyzed the second trimester chorionic villous sampling (CVS) samples and third trimester placentas. We found a significant decrease in expression of migration and invasion genes in CVS from preeclamptic pregnancies and significantly lower levels of JAG1 in placentas from pregnancies with early-onset preeclampsia with severe features. Our data support a role for Notch in mediating hypoxia-induced trophoblast migration, which may contribute to preeclampsia development.

Y-Box Binding Protein 1 Expression in Trophoblast Cells Promotes Fetal and Placental Development

Y-box binding protein 1 (YB-1) is pivotal for the regulation of cancerogenesis and inflammation. However, its involvement in pregnancy processes such as fetal and placental development remains to be elucidated. We studied Ybx1 (YB-1)^+/− heterozygous intercrossings and compared them to YB-1^+/+ wild-type (WT) combinations. Additionally, we generated trophoblast-specific YB-1-deficient mice by pairing FVB Cyp19-Cre females to YB-1^fl/fl males. YB-1^fl/fl-paired FVB WT females served as controls. Serial in vivo ultrasound measurements were performed to assess fetal and placental parameters. After sacrificing the females, implantation and abortion rates were recorded, spiral artery (SA) remodeling was analyzed and fetal and placental weights were determined. Compared to YB-1^+/+ counterparts, YB-1^+/− females showed reduced implantation areas at gestation day (GD)10, insufficiently remodeled SAs at GD12, increased placental diameter/thickness ratios at GD14 and reduced placental and fetal weights at GD14. Compared to WT, Cyp19-Cre females with YB-1-deficient placentas showed reduced implantation areas at GD8, 10 and 12; decreased placental areas and diameters at GD10 and 12; diminished placental thicknesses at GD12; as well as reduced placental weights at GD12 and 14. In conclusion, our data suggest haploinsufficiency of YB-1 resulting in disturbed fetal and placental development. Moreover, we provide the first evidence for the relevance of trophoblast-specific YB-1 for placentation.