Differential expression and regulation of Runx1 in mouse uterus during the peri-implantation period

Lineage tracing studies suggest that the placenta is not a de novo source of hematopoietic stem cells

Definitive hematopoietic stem and progenitor cells (HSPCs) arise from a small number of hemogenic endothelial cells (HECs) within the developing embryo. Understanding the origin and ontogeny of HSPCs is of considerable interest and potential therapeutic value. It has been proposed that the murine placenta contains HECs that differentiate into HSPCs. However, during human gestation HSPCs arise in the aorta considerably earlier than when they can first be detected in the placenta, suggesting that the placenta may primarily serve as a niche. We found that the Runx1 transcription factor, which is required to generate HSPCs from HECs, is not expressed by mouse placental ECs. To definitively determine whether the mouse placenta is a site of HSPC emergence, we performed lineage tracing experiments with a Hoxa13Cre allele that specifically labels ECs in the placenta and umbilical cord (UC), but not in the yolk sac or embryo. Immunostaining revealed Hoxa13Cre lineage-traced HECs and HSPCs in the UC, a known site of HECs, but not the placenta. Consistent with these findings, ECs harvested from the E10.5 aorta and UC, but not the placenta, gave rise to hematopoietic cells ex vivo, while colony forming assays using E14.5 fetal liver revealed only 2% of HSPCs arose from Hoxa13-expressing precursors. In contrast, the pan-EC Cdh5-CreERT2 allele labeled most HSPCs in the mouse placenta. Lastly, we found that RUNX1 and other HEC genes were not expressed in first-trimester human placenta villous ECs, suggesting that human placenta is not hemogenic. Our findings demonstrate that the placenta functions as a site for expansion of HSPCs that arise within the embryo proper and is not a primary site of HSPC emergence.

Runx1 regulates critical factors that control uterine angiogenesis and trophoblast differentiation during placental development

During early pregnancy in humans and rodents, uterine stromal cells undergo a remarkable differentiation to form the decidua, a transient maternal tissue that supports the growing fetus. It is important to understand the key decidual pathways that orchestrate the proper development of the placenta, a key structure at the maternal-fetal interface. We discovered that ablation of expression of the transcription factor Runx1 in decidual stromal cells in a conditional Runx1-null mouse model (Runx1^d/d) causes fetal lethality during placentation. Further phenotypic analysis revealed that uteri of pregnant Runx1^d/d mice exhibited severely compromised decidual angiogenesis and a lack of trophoblast differentiation and migration, resulting in impaired spiral artery remodeling. Gene expression profiling using uteri from Runx1^d/d and control mice revealed that Runx1 directly controls the decidual expression of the gap junction protein connexin 43 (also known as GJA1), which was previously shown to be essential for decidual angiogenesis. Our study also revealed that Runx1 controls the expression of insulin-like growth factor (IGF) 2 and IGF-binding protein 4 (IGFBP4) during early pregnancy. While Runx1 deficiency drastically reduced the production of IGF2 by the decidual cells, we observed concurrent elevated expression of the IGFBP4, which regulates the bioavailability of IGFs, thereby controlling trophoblast differentiation. We posit that dysregulated expression of GJA1, IGF2, and IGFBP4 in Runx1^d/d decidua contributes to the observed defects in uterine angiogenesis, trophoblast differentiation, and vascular remodeling. This study therefore provides unique insights into key maternal pathways that control the early phases of maternal-fetal interactions within a critical window during placental development.

Runx1 regulates critical factors that control uterine angiogenesis and trophoblast differentiation during placental development

During early pregnancy in humans and rodents, uterine stromal cells undergo a remarkable differentiation to form the decidua, a transient maternal tissue that supports the growing fetus. It is important to understand the key decidual pathways that orchestrate the proper development of the placenta, a key structure at the maternal-fetal interface. We discovered that ablation of expression of the transcription factor Runx1 in decidual stromal cells in a conditional Runx1 -null mouse model ( Runx1 ^d/d ) causes fetal lethality during placentation. Further phenotypic analysis revealed that uteri of pregnant Runx1 ^d/d mice exhibited severely compromised decidual angiogenesis, and a lack of trophoblast differentiation and migration, resulting in impaired spiral artery remodeling. Gene expression profiling using uteri from Runx1 ^d/d and control mice revealed that Runx1 directly controls the decidual expression of the gap junction protein connexin 43 (also known as GJA1), which was previously shown to be essential for decidual angiogenesis. Our study also revealed a critical role of Runx1 in controlling insulin-like growth factor (IGF) signaling at the maternal-fetal interface. While Runx1-deficiency drastically reduced the production of IGF2 by the decidual cells, we observed concurrent elevated expression of the IGF-binding protein 4 (IGFBP4), which regulates the bioavailability of IGFs thereby controlling trophoblast differentiation. We posit that dysregulated expression of GJA1, IGF2, and IGFBP4 in Runx1 ^d/d decidua contributes to the observed defects in uterine angiogenesis, trophoblast differentiation, and vascular remodeling. This study therefore provides unique insights into key maternal pathways that control the early phases of maternal-fetal interactions within a critical window during placental development.

SIGNIFICANCE

A clear understanding of the maternal pathways that ensure coordination of uterine differentiation and angiogenesis with embryonic growth during the critical early stages of placenta formation still eludes us. The present study reveals that the transcription factor Runx1 controls a set of molecular, cellular, and integrative mechanisms that mediate maternal adaptive responses controlling uterine angiogenesis, trophoblast differentiation, and resultant uterine vascular remodeling, which are essential steps during placenta development.

The spatial and temporal distribution of cationic and anionic radicals in early embryo implantation

The main objective of this study is to obtain some knowledge of cationic and anionic radicals in early embryo implantation in mice. The method used in this study is known as histochemical staining, in which Xylidine ponceau was used at pH 2.5 and toluidine blue was used at pH 4.0. We detected the change in glycosaminoglycans and total proteins in the endometrial stroma during the preimplantation of mice. This study revealed that the distribution patterns of cationic radicals and anionic radicals are similar on days 4 and 5 of pregnancy. However, there was a distinct difference between cationic radicals and anionic radicals on day 8 of pregnancy. The distribution pattern of cationic radicals is more concentrated in the stroma near the conceptus. Laboratory studies on histochemical stain provide more information about early embryo implantation.

Identification of Gene Expression Changes Associated With Uterine Receptivity in Mice

The mouse is a widely used animal model for studying human reproduction. Although global gene expression changes associated with human uterine receptivity have been determined by independent groups, the same studies in the mouse are scarce. The extent of similarities/differences between mice and humans on uterine receptivity at the molecular level remains to be determined. In the present study, we analyzed global gene expression changes in receptive uterus on day 4 of pregnancy compared to non-receptive uterus on day 3 of pregnancy in mice. A total of 541 differentially expressed genes were identified, of which 316 genes were up-regulated and 225 genes were down-regulated in receptive uterus compared to non-receptive uterus. Gene ontology and gene network analysis highlighted the activation of inflammatory response in the receptive uterus. By analyzing the promoter sequences of differentially expressed genes, we identified 12 causal transcription factors. Through connectivity map (CMap) analysis, we revealed several compounds with potential anti-receptivity activity. Finally, we performed a cross-species comparison against human uterine receptivity from a published dataset. Our study provides a valuable resource for understanding the molecular mechanism underlying uterine receptivity in mice.

The mammalian decidual cell evolved from a cellular stress response

Among animal species, cell types vary greatly in terms of number and kind. The number of cell types found within an organism differs considerably between species, and cell type diversity is a significant contributor to differences in organismal structure and function. These observations suggest that cell type origination is a significant source of evolutionary novelty. The molecular mechanisms that result in the evolution of novel cell types, however, are poorly understood. Here, we show that a novel cell type of eutherians mammals, the decidual stromal cell (DSC), evolved by rewiring an ancestral cellular stress response. We isolated the precursor cell type of DSCs, endometrial stromal fibroblasts (ESFs), from the opossum Monodelphis domestica. We show that, in opossum ESFs, the majority of decidual core regulatory genes respond to decidualizing signals but do not regulate decidual effector genes. Rather, in opossum ESFs, decidual transcription factors function in apoptotic and oxidative stress response. We propose that rewiring of cellular stress responses was an important mechanism for the evolution of the eutherian decidual cell type.

Runx2 acts downstream of C/EBPβ to regulate the differentiation of uterine stromal cells in mice

Although Runx2 is involved in the regulation of cellular differentiation, its physiological roles in the differentiation of uterine stromal cells during decidualization still remain unknown. The aim of this study was to examine the expression, regulation and function of Runx2 in mouse uterus during decidualization. The results showed that Runx2 was highly expressed in the decidua and oil-induced decidualized cells. In the uterine stromal cells, recombinant human Runx2 (rRunx2) could induce the expression of Prl8a2 and Prl3c1 which are two well-known differentiation markers for decidualization, while inhibition of Runx2 with specific siRNA reduced their expression. Further study found that rRunx2 could improve the expression of Prl8a2 and Prl3c1 in the C/EBPβ siRNA-transfected stromal cells. In the stromal cells, cAMP analogue 8-Br-cAMP could induce the expression of Runx2. Moreover, the induction was blocked by PKA inhibitor H89. Simultaneously, attenuation of C/EBPβ with siRNA could also reduce the cAMP-induced Runx2 expression. Furthermore, siRNA-mediated silencing of Runx2 expression alleviated the effects of cAMP on the differentiation of stromal cells. Runx2 might act downstream of C/EBPβ to regulate the expression of Cox-2, Vegf and Mmp9 in the uterine stromal cells. Collectively, Runx2 may play an important role during mouse decidualization.