Although the polygonal shape of epithelial cells has been drawing the attention of scientists for several centuries, only a decade and a half ago it was demonstrated that distributions of polygon types (DOPTs) are similar in proliferative epithelia of many different plant and animal species. In this study, we show that hyper-proliferation of cancer cells disrupts this universal paradigm and results in randomly organized epithelial structures. Examining non-synchronized and synchronized HeLa cervix cells, we suppose that the spread of cell sizes is the main parameter controlling the DOPT in the cancer cell monolayers. To test this hypothesis, we develop a theory of morphologically similar random polygonal packings. By analysing differences between tumoural and normal epithelial cell monolayers, we conclude that the latter have more ordered structures because of their lower proliferation rates and, consequently, more effective relaxation of mechanical stress associated with cell division and growth. To explain the structural features of normal proliferative epithelium, we take into account the spread of cell sizes in the monolayer. The proposed theory also rationalizes some highly ordered unconventional post-mitotic epithelia.

Le transport ultra-efficace de l'eau et des ions à l'échelle nanométrique est étudié par des simulations de dynamique moléculaire. Les nanotubes de carbone (CNTs) sont utilisés ici comme dispositifs nanofluidiques en raison de leur structure interne lisse et du compromis d'une composition très simple pour une énorme variété de propriétés. Le transport d'ions solvatés se déplaçant à l'intérieur du nanotube de carbone sous l'application d'une différence de potentiel externe a permis de mesurer le courant ionique établi à travers la zone interne du tube. Pour être le plus exhaustif possible, trois modèles d'eau populaires ont été testés pour étudier le transport ionique à l'intérieur de ce nanocanal artificiel. Les paramètres géométriques clés de la structure en carbone ont également été variés révélant une dépendance particulière de la conductance ionique à chaque paramètre étudié en accord avec le modèle théorique présenté dans cet article. Fichier révisé Version propre-Pour la mise en page Cliquez ici pour voir les références liées

The bacterial flagellar motor (BFM) is the membrane-embedded rotary molecular motor which turns the flagellum that provides thrust to many bacterial species. This large multimeric complex, composed of a few dozen constituent proteins, has emerged as a hallmark of dynamic subunit exchange. The stator units are inner-membrane ion channels which dynamically bind and unbind to the peptidoglycan at the rotor periphery, consuming the ion motive force (IMF) and applying torque to the rotor when bound. The dynamic exchange is known to be a function of the viscous load on the flagellum, allowing the bacterium to dynamically adapt to its local viscous environment, but the molecular mechanisms of exchange and mechanosensitivity remain to be revealed. Here, by actively perturbing the steady-state stator stoichiometry of individual motors, we reveal a stoichiometry-dependent asymmetry in stator remodeling kinetics. We interrogate the potential effect of next-neighbor interactions and local stator unit depletion and find that neither can explain the observed asymmetry. We then simulate and fit two mechanistically diverse models which recapitulate the asymmetry, finding stator assembly dynamics to be particularly well described by a two-state catch-bond mechanism.