| תקציר: | Hydra is a small freshwater animal with remarkable regenerative abilities, making it a powerful model for studying morphogenesis. During regeneration, the tissue undergoes dynamic remodeling, yet its 3D shape and cytoskeletal organization are still not fully characterized. Here, we use Multiview Lightsheet Microscopy, which provides long-term, high resolution 3D time-lapse imaging, to follow regenerating Hydra expressing LifeAct-GFP. We developed an analysis pipeline to segment the tissue, follow its outer surface and lumen shape, and extract spatial maps of the tissue shape and thickness as well as the actomyosin fiber organization. The actin cytoskeleton forms supra-cellular fibers, which organize into parallel nematic arrays with a characteristic defect pattern. We can align the tissue according to the nematic pattern and follow the morphological changes along the emerging body axis. We observe repeated cycles of osmotic lumen inflation at a constant rate that last for variable durations, followed by rapid deflation events. On a slower timescale, the volume of the surrounding tissue remains steady, enabling tissue thickness to serve as a coarse-grained measure of the isotropic tissue strain during regeneration. Using spherical harmonic decomposition of the shape and thickness fields, we quantify dynamic stretching modes and spatial correlations between tissue strain and the nematic organization of the actomyosin fibers. This framework allows us to study the interplay between large-scale tissue stretching and the spatial organization of the actomyosin network and its impact on body plan formation. |