Date : 11/10/2010
Internship proposal for : Master 1 or Master 2
CNRS & Université de la Méditerranée Case 907
Parc Scientifique de Luminy 13288 Marseille cedex 09
13009 Thomas Lecuit
Director : Loic Le Goff
Website : http://www.ibdml.univ-mrs.fr/equipes/equipe.php?id=6
Main discipline : Molecular biology / Biophysics
Loic Le Goff
phone : +33 491269314
Project 1 : interplay between tissue mechanics and growth
Project 2 : Growth through cooptation of neighboring tissues.
Subjects / Tools-Methodologies
1 : microscopy/image analysis/laser ablation/
Project1 : interplay between tissue mechanics and growth The aim of the projects is to analyse the potential repercussions of the observed internal stress on growth itself: Does this stress affect the way cells divide (frequency, orientation)? Or does it affect the way cells rearrange just after the division? Our analysis will focus on different regions of the disc, which experience varying degrees of tension, so as to correlate the amplitude of mechanical stress with a potentially stronger effect on cell divisions. The experimental work will rely on confocal microscopy observations and subsequent quantitative image analysis, laser ablation experiments, and local genetic alterations (clones) to locally affect tissue growth or tissue mechanics.
Project 2 : Growth through cooptation of neighboring tissues. We propose a second more prospective project, the aim of which is to study the spatio-temporal dynamics of cell identity in the wing disc. Indeed, a tissue can grow not only through cell divisions, but also through cooptation of neighbouring tissues. For example, it has been proposed that the precursor of the wing blade in the wing disc, grows partially through a recruitment of neighbouring cells that were not initially destined to become wing blade cells (they were precursor of the hinge, Zecca M & Struhl G. 2007). This recruitment has been proposed to proceed through a propagation of the selector gene vestigial that give cells the "wing" identity. The aim of the project is first to observe a potential propagation of vestigial expression (using a fluorescent reporter). This would represent an interesting example of the control of cell identity that is not transmitted clonally but rather through some spatio-temporal dynamics of gene expression. The second step of the project will be to quantify the respective contributions to the final size of the wing of growth through cell divisions and growth through cooptation of neighbours. Overall, this project will require to develop a way to image imaginal discs on longer time scales that what we can do now (>24h). In order to do so, we will develop a system to image wing discs directly within living larvae, that we will anesthetized for a brief instant (so as to stop parasitic movements such as heart beats) each time one acquires a confocal stack. For this, we will adapt a protocol initially developed for the study of neuromuscular junction development (Fuger et al. 2007).
These two projects will take place at the Institute for Developpemental Biology in Marseille, in a team that gathers biologists and physicists working on epithelial morphogenesis. All technical competences required for this multi-disciplinary project are available onsite (Drosophila genetics/soft matter physics/optical microscopy/image analysis).
Références : Lecuit T, Le Goff L.Orchestrating size and shape during morphogenesis. Nature. (2007) vol450, p189 Zecca M & Struhl G. Recruitment of cells into the drosophila wing primordium by a feed-forward circuit of vestigial autorégulation. Development. (2007) Fuger et al. Live imaging of synapse development and measuring protein dynamics using two-color fluorescence recovery after photo-bleaching at Drosophila synapses. Nat. Protocols (2007)
2 : microscopy/image analysis/genetics/
3 : The size and shape of biological tissues are robust. This robustness is associated with two form of plasticity: cellular rearrangements and growth trough cell divisions. The orchestration of these two processes dictates the final form of tissues (Lecuit&LeGoff 2007). The underlying processes of this orchestration are poorly known and we propose to address this question from an original point of view. We study how intercellular signals that orchestrate morphogenesis (morphogens) control the mechanics of tissues and thus could orient tissue growth (cell divisions) and tissue remodelling (exchange of neighbours). Our experimental model system is the imaginal disc of Drosophila, a monolayered epithelium that is the precursor of the adult wing. Living imaginal discs can be observed under a confocal microscope, and perturbed genetically and mechanically. We have recently developed an experimental paradigm that allows us to analyse how growth impacts on wing discs mechanics. We cultivated for several hours under a confocal microscope excised wing discs. A systematic analysis of cell deformations then revealed the emergence of internal mechanical stress within the tissue. These observations were supported by laser cutting experiments, that probe tension along cell junctions by measuring the speed of relaxation of these junctions once they have been destabilized with a laser cut.