Anterior visceral endoderm SMAD4 signaling specifies anterior embryonic patterning and head induction in mice

A single cell characterisation of human embryogenesis identifies pluripotency transitions and putative anterior hypoblast centre

Following implantation, the human embryo undergoes major morphogenetic transformations that establish the future body plan. While the molecular events underpinning this process are established in mice, they remain unknown in humans. Here we characterise key events of human embryo morphogenesis, in the period between implantation and gastrulation, using single-cell analyses and functional studies. First, the embryonic epiblast cells transition through different pluripotent states and act as a source of FGF signals that ensure proliferation of both embryonic and extra-embryonic tissues. In a subset of embryos, we identify a group of asymmetrically positioned extra-embryonic hypoblast cells expressing inhibitors of BMP, NODAL and WNT signalling pathways. We suggest that this group of cells can act as the anterior singalling centre to pattern the epiblast. These results provide insights into pluripotency state transitions, the role of FGF signalling and the specification of anterior-posterior axis during human embryo development.

Single cell analysis of early human embryos identifies key changes in pluripotency, the requirement of FGF signalling for embryo survival, and defines a putative anterior-like region of hypoblast cells, providing insights into how early human development is regulated.

Angiotensin II upregulates fibroblast-myofibroblast transition through Cx43-dependent CaMKII and TGF-β1 signaling in neonatal rat cardiac fibroblasts

In cardiac fibroblasts, angiotensin II (Ang II) can increase connexin 43 (Cx43) expression and promote calmodulin-dependent protein kinase II (CaMKII) activation. Cx43 overexpression is crucial for the fibroblast-myofibroblast transition. The main purpose of the present study was to investigate the role of CaMKII in regulating Cx43 expression and to determine whether the CaMKII/Cx43 pathway is essential for controlling fibroblast activation and differentiation. In vivo, 4 weeks of Ang II infusion enhanced CaMKII activation but reduced Cx43 expression in hearts undergoing fibrosis remodeling, while in cultured neonatal rat fibroblasts, CaMKII activation upregulated Cx43 expression via transforming growth factor-beta1 (TGF-β1). CaMKII inhibition by Ang-(1-7) or autocamtide 2-related inhibitory peptide reversed the Ang II-induced changes in Cx43 expression and attenuated Ang II-induced upregulation of alpha smooth muscle actin and TGF-β1 in both Ang II-infused rats and cultured fibroblasts. Based on the in vivo and in vitro experimental results, CaMKII plays a pivotal role in the Ang II-mediated fibroblast-myofibroblast transition by modulating the expressions of TGF-β1 and Cx43. We conclude that Ang II mediates the fibroblast-myofibroblast transition partially via the Ang II/CaMKII/TGF-β1/Cx43 signaling pathway.

Effect of the conditional knockout of bone marrow specific RIPK3 gene on bone marrow hematopoiesis in mice

Receptor-interacting serine-threonine kinase 3 (RIPk3) is a key signaling molecule in the regulation of cell apoptosis and necroptosis, it plays an important role in the pathophysiological changes of many hematologic diseases. However, the regulatory role of RIPk3 in programmed cell death (PCD) is not fully known. In this study, bone marrow-specific RIPk3 gene knockout homozygotes (RIPk3-/- mice) were established by homologous recombination. The physiological index of peripheral blood, the morphology and structure of the bone marrow, the bone marrow nucleated cells (BMNCs), the hemopoietic stem cells (HSCs), interleukin-6 (IL-6) level and the colony formation capacity of bone marrow hematopoietic progenitor cells were compared between RIPk3-/- mice and wild-type mice. The results showed that, the cell death rate of BMNCs in RIPk3-/- mice was significantly higher than that in control mice, indicated that RIPk3 gene knockout may cause damage to bone marrow cells to some extent. However, the bone marrow had normal structure and morphology in the bone marrow-specific RIPk3-knockout mice, and there were not significantly different between the two mice in most of the blood physiological indicators, and colony yields of hemopoietic stem/progenitor cells. Further study found that the bone marrow IL-6 level of the RIPk3-/- mice increased significantly, besides, the number of BMNCs and HSCs in the bone marrow of the RIPk3-/- mice increased considerably as compared with the control mice. The findings implies that bone marrow RIPk3 gene knockout may lead to the increase of BMNCs cell death, however, increased secretion of hematopoietic cytokines such as IL-6 may promote the proliferation of hematopoietic stem/progenitor cells and thus maintain the stability of bone marrow hematopoiesis. This hypothesis and the detailed mechanisms remain to be further investigated.

Nodal signaling from the visceral endoderm is required to maintain Nodal gene expression in the epiblast and drive DVE/AVE migration

In the early mouse embryo, a specialized population of extraembryonic visceral endoderm (VE) cells called the distal VE (DVE) arises at the tip of the egg cylinder stage embryo and then asymmetrically migrates to the prospective anterior, recruiting additional distal cells. Upon migration these cells, called the anterior VE (AVE), establish the anterior posterior (AP) axis by restricting gastrulation-inducing signals to the opposite pole. The Nodal-signaling pathway has been shown to have a critical role in the generation and migration of the DVE/AVE. The Nodal gene is expressed in both the VE and in the pluripotent epiblast, which gives rise to the germ layers. Previous findings have provided conflicting evidence as to the relative importance of Nodal signaling from the epiblast vs. VE for AP patterning. Here we show that conditional mutagenesis of the Nodal gene specifically within the VE leads to reduced Nodal expression levels in the epiblast and incomplete or failed DVE/AVE migration. These results support a required role for VE Nodal to maintain normal levels of expression in the epiblast, and suggest signaling from both VE and epiblast is important for DVE/AVE migration.

TGF-β and BMP signaling in osteoblast differentiation and bone formation

Transforming growth factor-beta (TGF-β)/bone morphogenic protein (BMP) signaling is involved in a vast majority of cellular processes and is fundamentally important throughout life. TGF-β/BMPs have widely recognized roles in bone formation during mammalian development and exhibit versatile regulatory functions in the body. Signaling transduction by TGF-β/BMPs is specifically through both canonical Smad-dependent pathways (TGF-β/BMP ligands, receptors and Smads) and non-canonical Smad-independent signaling pathway (e.g. p38 mitogen-activated protein kinase pathway, MAPK). Following TGF-β/BMP induction, both the Smad and p38 MAPK pathways converge at the Runx2 gene to control mesenchymal precursor cell differentiation. The coordinated activity of Runx2 and TGF-β/BMP-activated Smads is critical for formation of the skeleton. Recent advances in molecular and genetic studies using gene targeting in mice enable a better understanding of TGF-β/BMP signaling in bone and in the signaling networks underlying osteoblast differentiation and bone formation. This review summarizes the recent advances in our understanding of TGF-β/BMP signaling in bone from studies of genetic mouse models and human diseases caused by the disruption of TGF-β/BMP signaling. This review also highlights the different modes of cross-talk between TGF-β/BMP signaling and the signaling pathways of MAPK, Wnt, Hedgehog, Notch, and FGF in osteoblast differentiation and bone formation.