DISSECT is a tool to segment and explore cell and tissue mechanics in highly deformed 3D epithelia.

Understanding morphogenesis strongly relies on the characterization of tissue topology and mechanical properties deduced from imaging data. The development of new imaging techniques offers the possibility to go beyond the analysis of mostly flat surfaces and image and analyze complex tissue organization in depth. An important bottleneck in this field is the need to analyze imaging datasets and extract quantifications not only of cell and tissue morphology but also of the cytoskeletal network's organization in an automatized way. Here, we describe a method, called DISSECT, for DisPerSE (Discrete Persistent Structure Extractor)-based Segmentation and Exploration of Cells and Tissues, that offers the opportunity to extract automatically, in strongly deformed epithelia, a precise characterization of the spatial organization of a given cytoskeletal network combined with morphological quantifications in highly remodeled three-dimensional (3D) epithelial tissues. We believe that this method, applied here to Drosophila tissues, will be of general interest in the expanding field of morphogenesis and tissue biomechanics.

Mechano-biochemical marine stimulation of inversion, gastrulation, and endomesoderm specification in multicellular Eukaryota.

The evolutionary emergence of the primitive gut in Metazoa is one of the decisive events that conditioned the major evolutionary transition, leading to the origin of animal development. It is thought to have been induced by the specification of the endomesoderm (EM) into the multicellular tissue and its invagination (i.e., gastrulation). However, the biochemical signals underlying the evolutionary emergence of EM specification and gastrulation remain unknown. Herein, we find that hydrodynamic mechanical strains, reminiscent of soft marine flow, trigger active tissue invagination/gastrulation or curvature reversal via a Myo-II-dependent mechanotransductive process in both the metazoan Nematostella vectensis (cnidaria) and the multicellular choanoflagellate Choanoeca flexa. In the latter, our data suggest that the curvature reversal is associated with a sensory-behavioral feeding response. Additionally, like in bilaterian animals, gastrulation in the cnidarian Nematostella vectensis is shown to participate in the biochemical specification of the EM through mechanical activation of the ß-catenin pathway via the phosphorylation of Y654-ßcatenin. Choanoflagellates are considered the closest living relative to metazoans, and the common ancestor of choanoflagellates and metazoans dates back at least 700 million years. Therefore, the present findings using these evolutionarily distant species suggest that the primitive emergence of the gut in Metazoa may have been initiated in response to marine mechanical stress already in multicellular pre-Metazoa. Then, the evolutionary transition may have been achieved by specifying the EM via a mechanosensitive Y654-ßcatenin dependent mechanism, which appeared during early Metazoa evolution and is specifically conserved in all animals.