Spindle morphology and scaling

It has been known for a long time that there is a correlation between the size of a cell and the size of its organelles, including the spindle and the nucleus. This relationship is perhaps most striking during the first stages of embryogenesis, when cells change in size and shape several fold in the absence of growth. During this process, in order to accurately segregate chromosomes over a wide range of length scales, the spindle adapts its size and shape. These changes in size and shape ultimately relate to chromosome and cleavage plane positioning and are therefore crucial for the proper development of the embryo. Despite its importance the mechanisms that regulate spindle scaling, microtubule nucleation and  force generation remain elusive.  To gain insight into these questions, we combine mathematical modelling, biophysics and quantitative measurements of spindles during the early development of the zebrafish Danio rerio and in Xenopus laevis egg extract. 

Dynamics of chromatin organization in the nucleus

The spatio-temporal organization of chromatin in the nucleus is emerging as a fundamental factor regulating gene expression. Some recent studies have started to map the gene-wide chromatin interactions in the interphase nucleus, revealing some principles of chromosome organization into territories, and dramatic changes of chromatin organization and interactions during differentiation and lineage specification. These studies are typically based on chromosome capture techniques that require many nuclei and provide a static picture of chromosome organization in the nucleus. Therefore, the dynamics of chromatin reorganization and their contribution to lineage specification during differentiation are still poorly understood. We aim at uncovering the physical principles of chromatin organization in the nucleus. More specifically, we are interested in understanding how transcription factors, RNA polymerases, and other molecules are partitioned in the nucleoplasm, and how they contribute to the establishment of structures such as transcription factories, chromosome territories or chromatin states. To this end,  we are developing a new multi-scale live imaging approach to characterize nuclear organization dynamics at the single cell level based on the simultaneous characterization of both the local dynamics of RNA polymerases and transcription factors and the large scale behavior of chromatin. 

Design of new quantitative microscopy methods 

The spatial and temporal regulation of signaling controls a variety of biological phenomena ranging from the self-organization of cellular structures to the development of embryos and tissue formation. These processes arise ultimately from the combination of local molecular activities, interactions, and diffusion processes. Although some of the key molecular components involved in the formation of cellular structures and tissue formation are known, we currently lack a bottoms up understanding of how the behavior of these molecules gives rise to the formation of large structures, partly because of the lack of tools for both studying the spatial regulation of soluble proteins and biophysically characterizing the behavior of large structures and tissues. We are developing several new methods to characterize the microscopic behavior of molecules and the biophysics of large scale structures. These include custom-built light sheet microscopy for single molecule and whole embryo measurements, laser ablation to perturb and dissect the architecture of microtubule structures, quantitative polarization microscopy, and new fluorescence correlation spectroscopy approaches.