Research projects

Current projects

Our lab is interested in understanding the molecular and cellular mechanisms that regulate the morphogenesis and the growth of tissues during embryonic development. The system that we use to address these questions is the skeletal muscle and the animal model on which most of our research is done is the chick embryo.  

Due to its accessibility and amenability to in vivo manipulation, the chick embryo has been one of the most prolific in the past to uncover many fundamental mechanisms in developmental biology. Its success has been somewhat diminishing in the 80’s and 90’s due to the relative complexity of manipulating gene expression in vivo, and the concomitant improvement of transgenesis and knock-out techniques in other vertebrate systems. The combination of the newly developed electroporation technology (utilized to target in a time- and space-restricted manner the over-expression of candidate genes or inhibit their function in the embryo) with the classical approaches that have made the success of the avian model (e.g. the quail-chick chimera, or microsurgeries) and emerging live imaging technologies, opens new fields of investigation, until now restricted to more simple systems. This makes the chick embryo one of the most exciting and versatile model to characterize in an amniote embryo dynamic processes, such as tissue morphogenesis, whereby differentiated cells organize into functional organs.

Previous and current research

To date, most research in muscle research has focused on the molecular mechanisms underlying skeletal muscle induction, leading to the discovery of many of key regulatory genes and signalling pathways implicated in this process. However the later events of myogenic differentiation (morphogenesis, growth, fusion…) are much less understood. These are the questions on which we are focusing our attention.

Early morphogenesis of skeletal muscles
The muscle is a highly organised tissue, since its mechanical function depends in large part on the tight spatial organisation of its muscle fibres; the muscle therefore represents a good model where the molecular mechanisms regulating the morphogenesis of differentiated cells can be analyzed. Importantly, the embryonic muscles in the chick develop very similarly to mouse (and thus human), and therefore the avian embryo represents an ideal model to comprehend its formation in human.
 
We have developed a technique (somite electroporation in vivo) that allows us to specifically target the expression of various cDNA constructs in distinct cell populations that constitute the somite (which are the embryonic structures from which body and limb skeletal muscles derive). This allows us to perform lineage studies to follow the fate of cells along with development (e.g. using reporter genes, such as GFP) but also gain of function and  loss of function, due to the recent development of siRNAs technologies efficient in the chick embryo.
 
Moreover, the use of tissue-specific and inducible promoters allows the expression of any construct in a time- and place-controlled fashion that is unmatched in other animal models. We couple these manipulations with in vivo microsurgery and observation of cell behaviour, using classical, spinning-disk and two photon confocal technologies. While taken separately each of these techniques is relatively well established, combining them in live amniote embryos represents a major challenge that few, if any lab in the world have taken.
 
These approaches have enabled us, for instance, to decipher the morphogenetic movements that underlie the formation of skeletal muscles in vertebrates. Importantly, this has allowed us to identify the embryonic origin of a muscle progenitor population that constitutes the main source of skeletal muscle growth during embryonic and fetal life. The same population is at the origin of the satellite cells, i.e. adult muscle stem cells. Similar findings have been made in the mouse, thus demonstrating that the chick embryo represents a valid model to study skeletal muscle formation and growth in mammals, including man.

Ongoing work and future projects

In the future, we plan to follow two main lines of research. The first one is a logic continuation of our in vivo analysis of muscle morphogenesis in vertebrate development, addressing such important questions as the molecular mechanisms underlying muscle fusion. This line of research will build on our recognized expertise in the in vivo imaging of morphogenetic processes in live vertebrate embryos. The second part of our research will be a more systemic approach which aim is to identify gene networks implicated in the maintenance or on the contrary the differentiation of muscle stem cells.
 
Myoblast fusion
This research project proposes to utilise the knowledge we have acquired in the studies described above to analyze a later stage of muscle differentiation, the fusion of myoblasts, which is a necessary step for the growth of embryonic muscles. The recent use of cell-based therapy to treat muscular dystrophy in dogs makes the issue of understanding muscle cell fusion more than an academic issue: the ability to manipulate myoblast fusion may have therapeutic benefits, and an understanding of this mechanism in mammals will be needed if treatments are to exploit cell-based therapies.
 
Molecular networks regulating muscle stem cell proliferation and differentiation
Future work will focus on the identification of the gene networks that are implicated in the maintenance or on the contrary the differentiation of muscle stem cells. This will be accomplish in collaboration with a number of labs addressing similar question in various animal models, as well as labs specialised in systemic approaches of cell differentiation, and in mathematical modelling of biological processes. Once a model of a network of molecules is defined, we will test the robustness of the model, using the electroporation technique in the chick embryo.