Endoderme

Résumé

L'endoderme (entoblaste, endoblaste ou encore périsperme), par opposition à l'ectoderme et au mésoderme, est le feuillet interne de l'embryon de certains métazoaires (les eumétazoaires, qui signifie « vrais métazoaires », qui exclut le taxon des Éponges) qui se met en place au moment de la gastrulation. Il assure les fonctions nutritives dans l'embryon. Il a généralement pour rôle de donner naissance aux organes internes : ainsi, chez les mammifères, l'endoderme donne naissance aux glandes digestives et à l'épithélium qui tapisse le tube digestif et les voies respiratoires.En biologie végétale, l'endoderme correspond à la partie la plus interne du cortex (écorce) dans les jeunes tiges et les jeunes racines souvent constituées d'une seule couche de cellule. Plus la plante va devenir âgée, plus l'endoderme va se lignifier. Hypoblaste ou endoderme primitif Hypoblaste L'hypoblaste (ou endoderme primitif) est l'une des deux couches cellulaires dérivant de la masse cellula

Source officielle

https://fr.wikipedia.org/wiki/Endoderme

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Publications associées (19)

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In humans, mice, and other mammals key internal organs such as the gut, the lungs, the pancreas, and the liver all derive from the same embryonic tissue: the endoderm. The development of all of these structures thus depends on a same set of early cells, and on the developmental instructions provided to them by the embryo. One approach to study what these instructions might be is to study the behaviour of endoderm cells when they can not rely on embryonic instructions. That is, when they are generated and made to develop outside of the embryo. The rationale behind this approach, widely embraced by the field of synthetic embryology, is that the unguided development of specific embryonic cell types can provide a window to the observation of intrinsic characteristics of these cells and of fundamental developmental principles which might not be executed or manifested within the regulated environment of the embryo. Accordingly, in the work here described I use gastruloids, synthetic models of development made by aggregation of mouse embryonic stem cells in vitro to characterise the developmental behaviour of endoderm cells, in the absence of embryonic cues and in the absence of the extraembryonic tissues that they would usually rely on in vivo. In the first chapter of this thesis, I provide an introduction, overview, and review of our current understanding of the developmental biology of mouse endoderm as this develops in the embryo. I also introduce gastruloids as stem-cell-based experimental systems to study developmental mechanisms in vitro, decoupled from the constraints of experimental work with animals and animal embryos. Chapter 2 is dedicated to the earliest steps of endoderm development in gastruloids. I show when and where these cells appear, and how they sort as the gastruloid starts to mature. I find that endoderm cells follow similar spatial and temporal developmental patterns as those they would follow if they were in the embryo. I notably find that they always remain in an epithelial state, even as other cell types undergo mesenchymal transition. In Chapter 3 I describe surprising dynamics of endoderm cells over time, and how they self-organise into complex architectures at the core of the gastruloids. The epithelial domain that forms is dynamic and plastic, and partitions the gastruloids into interfacing compartments. Importantly, I reveal a significant endodermal component to this in vitro system, usually considered to be unstructured and neural/mesodermal in character. In Chapter 4 I show how the core endoderm compartment that I see forming in gastruloids is patterned along the longitudinal axis of the aggregate, with different cellular identities at different anterior-posterior position of the domain. By comparison with published embryonic datasets, I identify endodermal identities corresponding to the full spectrum of those that make up the gut tube in the embryo. Specifically, I describe how most endodermal cells adopt an early intestinal fate, and how many acquire anterior foregut identities. The work described in this thesis presents gastruloids as promising in vitro systems for the study of endoderm biology, morphogenesis, and mature fate specification, filling a gap within the field of synthetic embryology. It also notably opens translational possibilities to the use of gastruloids to produce endodermal cell types which may be otherwise difficult to generate using conventional directed differentiation methods.

EPFL2022

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Differential impact of TGF beta/SMAD signaling activity elicited by Activin A and Nodal on endoderm differentiation of epiblast stem cells

Pierre Osteil

Allocation of cells to an endodermal fate in the gastrulating embryo is driven by Nodal signaling and consequent activation of TGF beta pathway. In vitro methodologies striving to recapitulate the process of endoderm differentiation, however, use TGF beta family member Activin in place of Nodal. This is despite Activin not known to have an in vivo role in endoderm differentiation. In this study, five epiblast stem cell lines were subjected to directed differentiation using both Activin A and Nodal to induce endodermal fate. A reporter line harboring endoderm markers FoxA2 and Sox17 was further analyzed for TGF beta pathway activation and WNT response. We demonstrated that Activin A-treated cells remain more primitive streak-like when compared to Nodal-treated cells that have a molecular profile suggestive of more advanced differentiation. Activin A elicited a robust TGF beta/SMAD activity, enhanced WNT signaling activity and promoted the generation of DE precursors. Nodal treatment resulted in lower TGF beta/SMAD activity, and a weaker, sustained WNT response, and ultimately failed to upregulate endoderm markers. This is despite signaling response resembling more closely the activity seen in vivo. These findings emphasize the importance of understanding the downstream activities of Activin A and Nodal signaling in directing in vitro endoderm differentiation of primed-state epiblast stem cells.

WILEY2022

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Patterning and shaping the endoderm in vivo and in culture

Anne Grapin-Botton, Marine Marie Kraus

The definitive endoderm (DE) was first defined as the innermost germ layer found in all metazoan embryos. During development, it gives rise to a vast array of specialized epithelial cell types lining the respiratory and digestive systems, and contributes to associated organs such as thyroid, thymus, lungs, liver, and pancreas. In the adult, the DE provides a protective barrier against the environment and assumes many essential functions including digestion, nutrient absorption, and glucose homeostasis. Since general endoderm formation and patterning have been reviewed recently in a comprehensive manner [1], we will only provide a brief summary of how extracellular signals and downstream transcription factors control endoderm patterning. We will then focus on emerging work addressing the chromatin remodeling events occurring during endoderm organ specification and discuss how these molecular tools can be used to engineer endodermal organs in vitro.

Elsevier2012

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EPFL2022