Local and global changes in cell density induce reorganisation of 3D packing in a proliferating epithelium.

Tissue morphogenesis is intimately linked to the changes in shape and organisation of individual cells. In curved epithelia, cells can intercalate along their own apicobasal axes, adopting a shape named 'scutoid' that allows energy minimization in the tissue. Although several geometric and biophysical factors have been associated with this 3D reorganisation, the dynamic changes underlying scutoid formation in 3D epithelial packing remain poorly understood. Here, we use live imaging of the sea star embryo coupled with deep learning-based segmentation to dissect the relative contributions of cell density, tissue compaction and cell proliferation on epithelial architecture. We find that tissue compaction, which naturally occurs in the embryo, is necessary for the appearance of scutoids. Physical compression experiments identify cell density as the factor promoting scutoid formation at a global level. Finally, the comparison of the developing embryo with computational models indicates that the increase in the proportion of scutoids is directly associated with cell divisions. Our results suggest that apico-basal intercalations appearing immediately after mitosis may help accommodate the new cells within the tissue. We propose that proliferation in a compact epithelium induces 3D cell rearrangements during development.

Local and global changes in cell density induce reorganisation of 3D packing in a proliferating epithelium.

Tissue morphogenesis is intimately linked to the changes in shape and organisation of individual cells. In curved epithelia, cells can intercalate along their own apicobasal axes adopting a shape named "scutoid" that allows energy minimization in the tissue. Although several geometric and biophysical factors have been associated with this 3D reorganisation, the dynamic changes underlying scutoid formation in 3D epithelial packing remain poorly understood. Here we use live-imaging of the sea star embryo coupled with deep learning-based segmentation, to dissect the relative contributions of cell density, tissue compaction, and cell proliferation on epithelial architecture. We find that tissue compaction, which naturally occurs in the embryo, is necessary for the appearance of scutoids. Physical compression experiments identify cell density as the factor promoting scutoid formation at a global level. Finally, the comparison of the developing embryo with computational models indicates that the increase in the proportion of scutoids is directly associated with cell divisions. Our results suggest that apico-basal intercalations appearing just after mitosis may help accommodate the new cells within the tissue. We propose that proliferation in a compact epithelium induces 3D cell rearrangements during development.

Incorporation of a Metal Catalyst for the Ammonia Synthesis in a Ferroelectric Packed-Bed Plasma Reactor: Does It Really Matter?

Plasma-catalysis has been proposed as a potential alternative for the synthesis of ammonia. Studies in this area focus on the reaction mechanisms and the apparent synergy existing between processes occurring in the plasma phase and on the surface of the catalytic material. In the present study, we approach this problem using a parallel-plate packed-bed reactor with the gap between the electrodes filled with pellets of lead zirconate titanate (PZT), with this ferroelectric material modified with a coating layer of alumina (i.e., Al2O3/PZT) and the same alumina layer incorporating ruthenium nanoparticles (i.e., Ru-Al2O3/PZT). At ambient temperature, the electrical behavior of the ferroelectric packed-bed reactor differed for these three types of barriers, with the plasma current reaching a maximum when using Ru-Al2O3/PZT pellets. A systematic analysis of the reaction yield and energy efficiency for the ammonia synthesis reaction, at ambient temperature and at 190 °C and various electrical operating conditions, has demonstrated that the yield and the energy efficiency for the ammonia synthesis do not significantly improve when including ruthenium particles, even at temperatures at which an incipient catalytic activity could be inferred. Besides disregarding a net plasma-catalysis effect, reaction results highlight the positive role of the ferroelectric PZT as moderator of the discharge, that of Ru particles as plasma hot points, and that of the Al2O3 coating as a plasma cooling dielectric layer.