Date : 09/02/2011

Internship proposal for : Master 2

Laboratory
Molecular Genetics of Development
CNRS URA2578
Institut Pasteur
25 rue du Dr Roux 75015 PARIS
Director : Mrs Margaret Buckingham
Lab's website
Main discipline : Cell Biology

Supervisor
Mrs Sigolene Meilhac
email : Cet e-mail est protégé contre les robots collecteurs de mails, votre navigateur doit accepter le Javascript pour le voir
phone : +33 1 40 61 35 22

Subjects

1.: Morphogenesis
2.: Computer modelling

Tools and methodologies

1.: quantitative image analysis
2.: 3D visualization
3.: finite-element model

Summary of lab's interests

The laboratory of M. Buckingham is interested in the formation of muscles. It focuses on the regulatory genes which direct a cell into the myogenic programme of skeletal or cardiac muscle as well as on the cell lineages which contribute to these two striated muscle tissues. The model studied is the mouse, with genetic manipulation as an essential tool in our experimental approach. An approach of retrospective clonal analysis, using mice in which the cardiac actin gene is targeted with an nlaacZ reporter, has given insight into the cell dynamics underlying the growth of the myocardium. The group of S. Meilhac investigates the cell behaviour which underlies the morphogenesis of the heart. With its precise 3D geometry, which is essential to orchestrate the circulation of the blood, the heart provides a striking example of morphogenesis. The molecular pathways underlying the formation of the heart are well known and many mutants with heart defects are available. In particular polarity signalling is essential for the morphogenesis of the heart. However, knowledge at the cellular level is lacking, to understand how genes affect cell behaviour and how cell behaviour determines the shape of cardiac chambers. We investigate the polarity of myocardial cells and their behaviour and aim to model the morphogenesis of cardiac chambers. We adopt interdisciplinary approaches, to deal with the complexity of the geometry and with the non-stereotyped behaviour of cells in mammals. The project is relevant to medical applications such as congenital heart malformations.

Summary of project

The primordium of the heart is a tube, which extends and loops. Regions of the tube balloon out and expand to form the four cardiac chambers. The heart tube is initially composed of two tissues, endocardium and myocardium, the latter representing most of the cells. Myocardial cells are differentiated - they beat - however, they continue to divide. New myocardial cells are also being recruited in the cardiac tube at the poles, by differentiation of precursor cells. Our previous work has shown that the growth of the myocardium is polarised, as clones of cells grow with specific orientations in the different cardiac chambers. However, the respective contributions of different types of cell behaviour, such as cell proliferation, orientation of cell division, cell intercalation and cell recruitment, to the final shape of the embryonic mouse heart remain unknown, as well as the importance of external mechanical constraints. It is beyond human intuition to predict which 3D sha pe might emerge from a given combination of cell behaviour and polarity signals. Computer modelling has been central to the demonstration that polarity is key to the production of shapes such as the Snapdragon flower or the mouse limb bud. We plan to model the morphogenesis of the embryonic heart by computer simulation. For the study of morphogenesis on a larger scale, such as a whole organ, it is appropriate to consider the tissue as a continuum. In collaboration with E. Coen and A. Bangham (Norwich, UK), we use a Finite Element Analysis (FEA) model to simulate the overall shape changes of the heart. Biological data will feed the computer model, such as the initial heart geometry and the maps of cell division orientations and of cell proliferation rates. The tissue represented in the model will be deformed by the implementation of the initial cell behaviour and by additional forces such as those necessary to simulate heart looping. The parameters of growth will dynamically evolve with the deformation of the structure, the additional forces as well as with local stresses. We will test in silico which cell behaviour or force is important to the shaping of cardiac chambers. Ultimately, this model will be used to predict the shape of mutant hearts. The student will work with a physicist/biologist post-doc, Jean-Francois Le Garrec. The M2 project will involve work along three lines : 1. Starting from HREM (High Resolution Episcopic Microscopy) images of the developing heart, construct and optimize 3D-meshes (in .OBJ format) to be used as initial shape of the FEA model or as a control of the final simulated shape. This construction may be done for 2-4 stages (straight tube, early looped tube, late looped tube, embryonic heart). 2. Using results from proliferation assays or cell labelling experiments done in the lab, quantify the relative contributions of cell proliferation and cell recruitment from the heart poles to the overall growth of the heart tube. 3. Input biological data into the FEA model and run preliminary simulations to test how growth patterns lead to shape changes. This project can be extended for a PhD project including computer modelling and complementary biological experiments to test predictions of the model.