Szopos, M. | bioRxiv Science

bioRxiv2021

Spontaneous rotations in epithelia as an interplay between cell polarity and RhoA activity at boundaries.

Directed flows of cells in vivo are essential in morphogenesis. They shape living matter in phenomena involving cell mechanics and regulations of the acto-myosin cytoskeleton. However the onset of coherent motion is still poorly understood. Here we show that coherence is associated with spontaneous alignments of cell polarity by designing cellular rings of controlled dimensions. A tug-of-war between polarities dictates the onset of coherence, as assessed by tracking live cellular shapes and motions in various experimental conditions. In addition, we identify an internally driven constraint set by cellular acto-myosin cables at boundaries as essential to ensure coherence, and active force is generated as evaluated by the high RhoA activity. The cables are required to trigger coherence as shown by our numerical simulations based on a novel Vicsek-type model including free active boundaries. We quantitatively reproduce in silico coherence onsets and we predict criteria leading to coherence. Altogether, spontaneous coherent motion results from basic competitions between cell orientations and active cables at boundaries.

biophysics↗

bioRxiv2019

Biofluid modeling of the coupled eye-brain system and insights into simulated microgravity conditions

This work aims at investigating the interactions between the flow of fluids in the eyes and the brain and their potential implications in the development of visual impairment in astronauts, a condition also known as spaceflight associated neuro-ocular syndrome (SANS). To this end, we propose a reduced (0-dimensional) mathematical model of fluid flow in the eyes and brain, which is embedded into a simplified whole-body circulation model. In particular, the model accounts for: (i) the flows of blood and aqueous humor in the eyes; (ii) the flows of blood, cerebrospinal fluid and interstitial fluid in the brain; and (iii) their interactions. The model is used to simulate variations in intraocular pressure, intracranial pressure and blood flow due to microgravity conditions, which are thought to be critical factors in SANS. Specifically, the model predicts that both intracranial and intraocular pressures increase in microgravity, even though their respective trends may be different. In such conditions, ocular blood flow is predicted to decrease in the choroid and ciliary body circulations, whereas retinal circulation is found to be less susceptible to microgravity-induced alterations, owing to a purely mechanical component in perfusion control associated with the venous segments. These findings indicate that the particular anatomical architecture of venous drainage in the retina may be one of the reasons why most of the SANS alterations are not observed in the retina but, rather, in other vascular beds, particularly the choroid. Thus, clinical assessment of ocular venous function may be considered as a determinant SANS factor, for which astronauts could be screened on earth and in-flight.

physiology↗