IMAGING ACROSS SCALES – CATCHING CONCURRENT ORGANELLE DYNAMICS IN LIVING CELLS AND TISSUES

In animal development, timing matters. Phenomena operating within distinct levels—those of molecules, organelles, cells, or tissues, span the extremes of timescales and give rise to the clock work of development. Developmental programs are under genetic control; however, the physical basis of these processes lie within the components that drive it - molecules, organelles, cells, supracellular assemblies. Capturing these mechanisms requires imaging approaches that can span different scales, molecular to tissue level processes demand both high spatial and temporal resolutions simultaneously. In the first part, I will introduce light-sheet microscopy and exemplify cell biological studies using endosomal timekeeping of biochemical reactions at single cell levels. However, these approaches are limited by the absence of physiological context as cells are investigated in isolation. In the second part, I will describe imaging approaches based on Airy beam-based light sheet microscopy of organelles in tens to hundreds of cells in a few hundred micrometre-wide tissue environments that will enable. This approach achieves a typical resolution of 320 nm over 266 × 266 × 100 μm3 volumes at a temporal rate of 0.05 Hz that now allows tracking molecules and organelles in large living tissues. I will detail out how such imaging across scales allows discovering new phenomena in tissue morphogenesis using Drosophila as a model system, where we address how during germ band extension, the monolayer of cells from the central side wrap around the high curvature posterior pole onto the dorsal surface. We discover an interplay between curvature, waves of cell divisions within domains and tissue fluidization that work together to preserve segment boundaries. Finally, I will conclude by addressing data challenges, including visualization and analysis, and outlook on the future of biological problems that these approaches unravel.