Investigation of the mechanics of gastrulation in the chick embryo using new transgenic chicken lines

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An important goal of the study of development of higher animals including humans is to understand how hundreds of thousands to millions of cells assemble into tissues that make organs and structures that make up an organism and which mechanisms control and integrate these behaviours. This coordination of cell behaviours is especially important at a critical early stage in embryonic development, gastrulation. During gastrulation the main body plan of the embryo is laid down and the main body axes emerge. Gastrulation involves large-scale, long-range cell movements and tissue deformations during which cells of the three body layers, the ectoderm, the mesoderm and endoderm take up their correct positions in the embryo. The endoderm is located inner most in the embryo forming the lining of the digestive tract and associated glands. It is surrounded by a middle layer the mesoderm that will make the muscles and the skeleton. The mesoderm is surrounded by the outmost layer, the ectoderm, which will form the epidermis (skin) and the brain and nervous system. Defects in the coordination of cell movements during gastrulation results in death of the embryo or in less severe cases in many major birth defects, such as the various forms of spina bifida and diverse heart defects.We study the mechanism of gastrulation in the chick embryo, that has the advantage that development takes place in the egg outside the mother animal and is therefore easily accessible to experimental observation and manipulation. The embryo is also flat and translucent which helps observation of cell movement during gastrulation. Gastrulation in chick embryos greatly resembles gastrulation in humans, which means that findings can be extrapolated to human development. We study how different cell behaviours such as cell division, shape changes, differentiation and motion are coordinated to generate these three embryonic tissues through specific chemical and mechanical cell-cell signalling mechanisms. Since these processes are highly dynamic we use time lapse microscopy to visualise these behaviours of the around 500.000 cells that make up the embryo of this stage of development. To do this we have developed and built a novel type of microscope, a light-sheet fluorescence microscope, that allows us to see almost all the cells in the embryo of a special chicken line in which the membranes of cells are marked with a green fluorescent protein. We have also developed extensive computational methods to extract quantitative information about relevant cell and tissue behaviours that drive gastrulation under normal and experimentally perturbed conditions. In this project we specifically test the hypotheses that forces produced by cell behaviours such as cell growth and movement are instrumental in the coordination of the complex cell behaviours of many cells in the developing embryo. Furthermore we expect that these forces feedback on the control of gene expression controlling the location and quantity of the various different types of cells in the embryo. To test this hypothesis we will generate new chicken lines that allow us to monitor and perturb the activity of critical elements of the actin-myosin cytoskeleton of cells that is responsible for generating these forces and correlating these with distinct cell and tissue behaviours using the above described live imaging and data analysis methodology.