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in toto imaging of embryonic morphogenesis: collective cell movements and symmetry breaking

Final Report Summary - INTOTOMORPHOGENESIS (in toto imaging of embryonic morphogenesis: collective cell movements and symmetry breaking)

An embryo is shaped by a complex sequence of cell processes and morphogenetic events that are highly regulated both in time and space. Advances in genetics or in molecular and cell biology, provided insights and tools to improve our understanding of the mechanisms involved in embryonic development. However, most of the studies in developmental biology are limited to a few cells or to the scale of the entire organism without cellular resolution. In addition, the challenging experimental conditions often limit the investigation to static and qualitative analysis using fixed embryos. Hence, fundamental mechanisms involving the dynamic and stochastic interaction of large group of cells and the emergence of highly organized tissue-scale structures from local cell-cell interactions are poorly understood. During early stages of development, such mechanisms include symmetry breaking and specification of the body plan. Successive processes of symmetry breaking are occurring during the sequence of early morphogenesis. These fascinating events are raising fundamental questions that are still under debate and investigation. They are challenging to study and we believe their investigation would strongly benefit from an experimental approach that is in vivo, quantitative, dynamic, and multiscale, from the cell level to the scale of the organ or organism and that integrates both genetics and cell biology approaches. In parallel, advances in fluorescent reporters, microscopy and image processing, make possible investigating the dynamics of large cell populations in a developing embryo. It led to the emergence of the in toto imaging concept and provides a unique opportunity to study embryonic development from the scale of the cellular mechanisms to the entire organ or organism. in toto imaging of embryonic morphogenesis aims at imaging an entire organ or organism during its development and at analyzing the digital data in a quantitative manner. This promising approach involves several experimental challenges including the in vivo imaging of an entire organ or organism during its development in a manner that does not compromise normal biology and embryo viability. In addition, the complexity of the multidimensional data generated prevents any qualitative or manual analysis. Therefore, the large amount of biological information contained in these imaging datasets requires quantitative and computational analysis to be identified.
The main purpose of this project was to bring novel approaches and techniques for whole embryo imaging in order to dissect fundamental processes of embryonic development. The IRG grant was used to help the IRG researcher to start a new research activity mainly focused on the development of 2-photon excited fluorescence light-sheet microscopy (2pFLSM) within the Advanced Microscopy team at the Laboratory for Optics and Biosciences (LOB, Ecole Polytechnique, Palaiseau, France). 2pFLSM is a new technique with improved imaging depth, acquisition speed and low invasiveness compared to the state-of-the art and has been developed and characterized using model organisms, such as fruit fly and zebrafish embryos. Together with adapted image processing tools and data analysis, methodological innovations has been successfully applied to several studies, including heart development, axis specification and symmetry breaking in early embryos, Brainbow tissue analysis or whole-brain functional imaging.