The roles of ERAS during cell lineage specification of mouse early embryonic development

Eras encodes a Ras-like GTPase protein that was originally identified as an embryonic stem cell-specific Ras. ERAS has been known to be required for the growth of embryonic stem cells and stimulates somatic cell reprogramming, suggesting its roles on mouse early embryonic development. We now report a dynamic expression pattern of Eras during mouse peri-implantation development: its expression increases at the blastocyst stage, and specifically decreases in E7.5 mesoderm. In accordance with its expression pattern, the increased expression of Eras promotes cell proliferation through controlling AKT activation and the commitment from ground to primed state through ERK activation in mouse embryonic stem cells; and the reduced expression of Eras facilitates primitive streak and mesoderm formation through AKT inhibition during gastrulation. The expression of Eras is finely regulated to match its roles in mouse early embryonic development during which Eras expression is negatively regulated by the β-catenin pathway. Thus, beyond its well-known role on cell proliferation, ERAS may also play important roles in cell lineage specification during mouse early embryonic development.     

BMP-gated cell-cycle progression drives anoikis during mesenchymal collective migration

1. Download : Download high-res image (169KB)
2. Download : Download full-size image

     

Guidance by followers ensures long-range coordination of cell migration through α-catenin mechanoperception

1. Download : Download high-res image (312KB)
2. Download : Download full-size image

     

Temporal and contextual orchestration of cardiac fate by WNT‐BMP synergy and threshold

Cardiomyogenic development proceeds with a cascade of intricate signalling events that operate in a temporo‐spatial fashion to specify cardiac cell fate during early embryogenesis. In fact, conflicting reports exist regarding the role of Wnt/β‐catenin signalling during cardiomyogenesis. Here, we describe a dose‐dependent and temporal effect of Wnt/β‐catenin signalling on in vitro cardiomyogenesis using embryonic stem cells (ESCs) as a model system. We could demonstrate that canonical Wnt activation during early stage of differentiation either through ligand or by GSK3β inhibition helped in maintaining Oct4 and Nanog expressions, and in parallel, it promoted mesoderm and endoderm inductions. In contrast, it led to attenuation in cardiomyogenesis that was reversed by moderate concentration of DKK1, but not soluble Fz8. However, higher DKK1 could also block cardiomyogenesis, suggesting thereby governance of a particular signalling threshold underlying this developmental event. Interestingly, Wnt signalling activation at early stage modulated BMP4 expression in a stage‐specific manner. Wnt activation, synchronized with BMP4 and brachyury up‐regulation at early stage, correlated well with mesoderm induction. Conversely, Wnt activation led to BMP4 and Wnt5a down‐regulation at late stage culminating in cardiomyogenic attenuation. Our findings suggested the existence of precise regulatory machinery with context‐dependent role of Wnt for fine tuning mesoderm induction and its derivatives, through establishment of Wnt gradient during ESCs’ differentiation. Moreover, contrary to mere activation/inhibition, a specific threshold of Wnt and BMP and their synergy seemed necessary for providing the guiding cues in orchestrating mesoderm induction and subsequent cardiomyogenesis.     

Inability of mesoderm cells to locomote on the modified free surface of epithelial cell sheets in vitro

Summary Previous work has shown that when chick embryo mesoderm tissue is seeded onto the free, dorsal surface of established sheets of embryonic epithelial endoblast, the former penetrates the latter and spreads on the underlying artificial substratum. In this work, the surface charge on the epithelial sheet has been altered, prior to seeding the mesoderm, to ascertain whether such a change could alter the behavior of the mesoderm with respect to the free surface of the epithelium. Charge alteration was accomplished using the polycations, poly-l-lysine and dilysine. Surface charge characteristics were examined ultrastructurally using cationized and anionized ferritin. Results showed that although surface charge changes were detectable, there was no difference in the behavior of the mesoderm with respect to the endoblast. Neuraminidase did not detectably affect the epithelial surface charge. These results are consistent with the view that changes in substratum surface charge are not necessarily correlated with changes in adhesiveness.     

Embryonic stem (ES) cell-derived cardiomyocytes: A good candidate for cell therapy applications

During the last decade, embryonic stem cells (ESC) have unleashed new avenues in the field of developmental biology and emerged as a potential tool to understand the molecular mechanisms taking place during the process of differentiation from the embryonic stage to adult phenotype. Their uniqueness lies in retaining the capacity of unlimited proliferation and to differentiate into all somatic cells. Together with promising results from rodent models, ESC has raised great hope among for human ESC-based cell replacement therapy. ESC could potentially revolutionize medicine by providing a powerful and renewable cell source capable of replacing or repairing tissues that have been damaged in almost all degenerative diseases such as Parkinson's disease, myocardial infarction (MI) and diabetes. Somatic stem cells are an attractive option to explore for transplantation because they are autologous, but their differentiation potential is very limited. Currently, the major sources of somatic cells used for basic research and clinical trials come from bone marrow. But their widespread acceptability has not been gained because many of the results are confusing and inconsistent. The focus here is on human embryonic stem cells (hESCs), using methods to induce their differentiation to cardiomyocytes in vitro. Their properties in relation to primary human cardiomyocytes and their ability to integrate into host myocardium have been investigated into how they can enhance cardiac function. However, important aspects of stem cell biology and the transplantation process remain unresolved. In summary, this review updates the recent progress of ES cell research in cell therapy, discusses the problems in the practical utility of ESC, and evaluates how far this adjunctive experimental approach can be successful.     

FGF receptor gene expression and its regulation by FGF signaling during early zebrafish development

The expression of all four fgfr genes was extensively examined throughout early embryogenesis of the zebrafish (Danio rerio). fgfr1 alone was expressed maternally throughout the blastoderm, and then zygotically in the anterior neural plate and presomitic mesoderm. fgfr4 expression was first detected in late blastulae and was gradually restricted to the brain. fgfr2 and fgfr3 expression were initiated in early and late gastrulae, respectively; fgfr2 was expressed in the anterior neural plate and somitic mesoderm, whereas fgfr3 was activated in the axial mesoderm and then in the midbrain and somitic mesoderm. During somitogenesis, each of these fgfr genes was expressed in a characteristic manner in the brain. Using an FGF signal inhibitor, dominant-negative FGF receptors and fgf8.1/fgf8a mutants, we found that fgfr expression is directly or indirectly regulated by FGF signaling during epiboly and at the end of somitogenesis, revealing the presence of an autoregulatory mechanism.     

Cyclical expression of the Notch/Wnt regulator Nrarp requires modulation by Dll3 in somitogenesis

Delta-like 3 (Dll3) is a divergent ligand and modulator of the Notch signaling pathway only identified so far in mammals. Null mutations of Dll3 disrupt cycling expression of Notch targets Hes1, Hes5, and Lfng, but not of Hes7. Compared with Dll1 or Notch1, the effects of Dll3 mutations are less severe for gene expression in the presomitic mesoderm, yet severe segmentation phenotypes and vertebral defects result in both human and mouse. Reasoning that Dll3 specifically disrupts key regulators of somite cycling, we carried out functional analysis to identify targets accounting for the segmental phenotype. Using microdissected embryonic tissue from somitic and presomitic mesodermal tissue, we identified new genes enriched in these tissues, including Limch1, Rhpn2, and A130022J15Rik. Surprisingly, we only identified a small number of genes disrupted by the Dll3 mutation. These include Uncx, a somite gene required for rib and vertebral patterning, and Nrarp, a regulator of Notch/Wnt signaling in zebrafish and a cycling gene in mouse. To determine the effects of Dll3 mutation on Nrarp, we characterized the cycling expression of this gene from early (8.5 dpc) to late (10.5 dpc) somitogenesis. Nrarp displays a distinct pattern of cycling phases when compared to Lfng and Axin2 (a Wnt pathway gene) at 9.5 dpc but appears to be in phase with Lfng by 10.5 dpc. Nrarp cycling appears to require Dll3 but not Lfng modulation. In Dll3 null embryos, Nrarp displayed static patterns. However, in Lfng null embryos, Nrarp appeared static at 8.5 dpc but resumed cycling expression by 9.5 and dynamic expression at 10.5 dpc stages. By contrast, in Wnt3a null embryos, Nrarp expression was completely absent in the presomitic mesoderm. Towards identifying the role of Dll3 in regulating somitogenesis, Nrarp emerges as a potentially important regulator that requires Dll3 but not Lfng for normal function.