Feuillet embryonnaire

Résumé

vignette|Croquis d'un embryon de poulet, tiré des Contributions à la croissance du poussin dans l’œuf, de Chr.-H. von Pander. Un feuillet embryonnaire est un groupe de cellules produit durant l'embryogenèse des métazoaires. Cette notion a été introduite en 1828 par Chr.-H. von Pander (1794-1865) et K.-E. vo Baer pour expliquer les analogies qu'ils avaient mises en évidence dans le développement pré-natal de différentes espèces animales. Observations anatomiques Lors de la formation de l'embryon, les cellules s'organisent en feuillets de cellules, qui se distinguent les uns des autres durant la gastrulation : le feuillet extérieur s'appelle alors ectoderme, et le feuillet intérieur, endoderme. Chez les métazoaires diploblastiques ou diblastiques, il n'y a que ces deux feuillets, séparés par une matrice extracellulaire hydratée appelée mésoglée. Chez les métazoaires triploblastiques ou triblastiques, le feuillet intermédiaire forme un véritable tissu appelé mésoderme. Chacun

Source officielle

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

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Squamous stratified epithelia tissues are self-renewing, which quality implies the existence of stem cells. In skin the presence of bona fide multipotent stem cells has been demonstrated by long-term, serial grafting assays. We isolated, cultivated and expanded clonogenic keratinocytes from stratified epithelia of rodents (mouse and/or rat cornea, hairy and glabrous skin, oesophagus, buccal cavity and vagina). Just like mutipotent stem cells present in skin, clonogenic epithelial cells present in the stratified epithelia of rodents are able to respond to skin and hair morphogenetic signals, thereby forming de novo cycling hair follicles, sebaceous glands and contributing to skin formation in transplantation assays. Our results show that, irrespective of their germ layer origin, the ability of clonogenic cells from stratified epithelia to respond to skin and hair morphogenetic signals is part of their intrinsic competence. Our RT-PCR results indicate that cell culture acts as a revealer of this competence and that cell culture does not alter this intrinsic competence. These observations strongly suggest that stem cells of stratified epithelia, irrespective of their germ layer origin, share common characteristics and are closely related, if not functionally identical. Therefore they may be interchangeable, thus opening the door for therapeutic use of one stratified epithelium to heal another.

EPFL2008

Chargement

Probing the differential adhesion hypothesis in the mammary gland using different bioengineered cell culture substrata

Léa Chanson

During tissue development, cells are able to form different layers and to self organize. At the moment, there are two principal hypotheses that try to explain cell sorting. The so called differential adhesion hypothesis (DAH) posits that cells organize according to the level of expression of cell-cell adhesion proteins so as to reduce free-energy in the system. The second hypothesis explains the formation of different germ layers according to cortical tension among cells of distinct phenotypes. For this work, we wanted to study cell sorting in the mammary glands, which are bilayered branching structures composed of outer myoepithelial (MEP) and inner luminal epithelial cells (LEP). Both sorting hypotheses were tested using bioengineered cell culture substrata. Using arrays of micro-wells that were cast in polydimethylsiloxane (PDMS) coupled with quantitative image analysis, we observed that cell sorting occurred over time between LEP and MEP that were isolated by fluorescence-activated cell sorting from primary human mammary epithelial cells. Inhibitors of specific cadherins were able to prevent cell sorting in accordance with the DAH. However, chemical inhibitors of cytoskeletal proteins, which effectively prevented the cells from modulating their innate elasticity, also prevented cell sorting suggesting cortical tension also plays an important role. Thus, our data suggests a third hypothesis, which is essentially a unification of the original two, such that differences in cortical tension are essentially lineage-specific and are governed wholly or in-part by cell-cell adhesion molecules. Experimental resolution of this hypothesis is being actively pursued

2009

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The Role of Nodal Processing in Pluripotent Progenitors

Anja Dietze

Nodal and its co-receptors of the EGF-CFC family are essential during chordate development, both to maintain pluripotent progenitor cells and to subsequently coordinate their allocation to the different germ layers. How these distinct Nodal activities are kept in balance is unknown. Previous work in our laboratory established that the Nodal proprotein must be cleaved by proprotein convertases (PC) to induce itself on time in the mouse epiblast. However, expression of a knock-in allele encoding a PC-resistant mutant Nodal precursor (Nr) is sufficient to induce a subset of Nodal target genes during gastrulation, including Fgf4 in the epiblast, and Bmp4 in extraembryonic ectoderm (ExE). Here, I extend these findings by showing that these NodalNr/Nr embryos also partially maintain a panel of trophoblast stem cell (TSC) markers. To better define how Nodal maintains pluripotency and how it might signal to TSCs in the ExE, and as a means to genetically uncouple Nodal production from processing, I treated cultured TSCs and NodallacZ/lacZ embryonic stem cells (ESCs) with recombinant Nodal or with cleavage-resistant mutant Nodal precursor. I show that recombinant mature Nodal stimulates Smad2 phosphorylation in both ESCs and TSCs, even though the latter do not express Nodal coreceptors of the EGF-CFC family. In contrast, recombinant Nr failed to activate the canonical Smad pathway in either cell type, and hence preferentially stimulated Jnk and p38 MAPK signaling. Yet, none of these activities were sufficient to promote self-renewal of mouse ESCs or TSCs under any of the culture conditions examined. Using lentiviral overexpression of constitutively active receptors with mutations in the Smad2,3 binding site, I observed that TSC stemness apparently can be maintained independently of Smad2,3 activation. These results suggest that mature Nodal or its unprocessed precursor likely promote the self-renewal of TSCs in vivo through a non-canonical, Smad-independent signaling pathway, but that available recombinant proteins for unknown reasons cannot fully mimic this activity in vitro, at least under the conditions examined.

EPFL2011

Chargement

The Role of Nodal Processing in Pluripotent Progenitors

Anja Dietze

EPFL2011