Mimétisme

Résumé

Le mimétisme est une stratégie adaptative d'imitation. Elle permet par exemple à une espèce d'échapper à d'éventuels prédateurs. Le processus le plus étudié est le mimétisme visuel, mais il existe aussi des mimétismes chimique (olfactif, gustatif), acoustique, tactile, comportemental. Les stratégies mimétiques visuelles sont de divers types, comme les espèces qui disposent de moyens d'échapper à la vision du prédateur — on parle alors de camouflage par mimétisme cryptique, homomorphique ou homotypique — ou comme le fait de se faire passer pour une autre espèce, par exemple en se parant des attributs d'espèces non comestibles, voire dangereuses. Toutefois, le mimétisme peut répondre à d'autres contraintes, telles que la reproduction (cas des coucous ou de certaines orchidées), ou la prédation (cas de la blennie dévoreuse). Il existe une différence majeure entre le mimétisme et le camouflage du point de vue de leur évolution : si l'aptitude au camouflage, notamment par la couleur ou la texture, peut se développer assez rapidement au sein d'une population par le jeu des mutations et de la sélection (exemple de la phalène du bouleau), le mimétisme au contraire implique un mécanisme plus complexe de coévolution mettant en jeu trois espèces : l'espèce servant de « modèle », l'espèce imitatrice et l'espèce dupée. C'est l'entomologiste britannique Henry Walter Bates (1825-1892), naturaliste et explorateur ayant passé onze ans en Amazonie, qui émit pour la première fois une théorie sur le mimétisme à propos de papillons d'aspects similaires, bien que n'étant pas d'espèces proches : une espèce inoffensive profitant de la répulsion provoquée par une espèce vénéneuse ou venimeuse. Il créa alors le mot anglais mimicry, un néologisme façonné sur le grec et qui signifie « capacité à imiter ». Fritz Müller (1834-1895), un zoologiste allemand, expliqua pour la première fois en 1878 le phénomène selon lequel deux espèces non mangeables différentes vont adopter une même apparence de leur livrée, leurs prédateurs apprenant plus vite à se méfier d'elles.

Source officielle

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

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Publications associées (3)

Concepts associés (86)

Cours associés (1)

Séances de cours associées (12)

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

Coating high aspect-ratio channels of multi-aperture vision sensor using Micromoulding in Capillaries (MIMIC)

Gabriel Safar

The motivation for this project is to prevent optical cross-talk in an optical sensor array, named ommatidia and fabricated in the CURVACE project. The goals of the project are to show that Micromoulding in Capillaries (or MIMIC) is a very effective and cost-efficient method to encapsulate sensors with high aspect-ratio structures. To this end, many challenging problems have been solved. Many achievements have been attained, including the fabrication of high aspect-ratio (10:1) structured PDMS moulds (height 650μm) and the fabrication of tightly packed high aspect-ratio SU-8 structures (height 650μm). Furthermore, the successful alignment of high aspect-ratio structured PDMS moulds into high aspect-ratio sensor structures, in order to perform encapsulation, has also been performed. These results show that use of the MIMIC technique for sensor encapsulation is promising, both in terms of performance and in terms of cost-effectiveness.

2011

In the domain of regenerative medicine research there are many fronts aimed at increasing our understanding of induced pluripotent, embryonic and adult stem cells. Recently a new front has appeared, stem cell niches, the microenvironment that is a crucial component in the regulation of stem cells. New in vitro platforms are continually being created to answer the multitude of biological questions that surround stem cell niches. The transition from in vitro to in vivo is a heavy setback in cellular research due to a huge gap between the two conditions, which can only be reduced if the in vitro conditions better mimic those found in vivo. This project has reduced the gap and has the potential to continue minimizing the differences between the two conditions in the field of muscle stem cell research. Through a combination of the forefront techniques in biological research, we were able to create a new innovative bioengineered platform, a bipolar hydrogel microenvironment. First, we took advantage of polyethylene glycol (PEG) hydrogels, which are highly hydrophilic polymer networks that have properties that mimic physiologic tissue, including high water content and low Young's Modulus. Microfabrication techniques allowed us to topographically pattern the hydrogel at micro-dimensions resembling the native cell environment. Utilizing microfluidics and micro-printing techniques, the three-dimensional hydrogel surface was also patterned with tethered niche proteins found in the in vivo muscle stem cell niche. The swelling properties of the PEG hydrogel were considered as an advantage and controlled to form niche gaps with physical properties that were tuned to correspond to those found in vivo. This new complex and controlled surface for cells to be cultured on is a tool, which will allow biologists to probe new questions and gain insight into the regulatory networks that control cell fate

2009