Axonal beading, or the formation of a series of swellings along the axon, and retraction are commonly observed shape transformations that precede axonal atrophy in Alzheimer's disease, Parkinson's disease, and other neurodegenerative conditions. The mechanisms driving these morphological transformations are poorly understood. Here, we report controlled experiments that can induce either beading or retraction and follow the time evolution of these responses. By making quantitative analysis of the shape modes under different conditions, measurement of membrane tension, and using theoretical considerations, we argue that membrane tension is the main driving force that pushes cytosol out of the axon when microtubules are degraded, causing axonal thinning. Under pharmacological perturbation, atrophy is always retrograde, and this is set by a gradient in the microtubule stability. The nature of microtubule depolymerization dictates the type of shape transformation, vis-a `-vis beading or retraction. Elucidating the mechanisms of these shape transformations may facilitate development of strategies to prevent or arrest axonal atrophy due to neurodegenerative conditions.
Axonal beading-formation of a series of swellings along the axon-and retraction are commonly observed shape transformations that precede axonal atrophy in Alzheimer's, Parkinson, and other neurodegenerative conditions. The mechanisms driving these morphological transformations are poorly understood. Here we report controlled experiments which can induce either beading or retraction and follow the time evolution of these responses. By making quantitative analysis of the shape modes under different conditions, measurement of membrane tension, and using theoretical considerations, we argue that membrane tension is the main driving force that pushes cytosol out of the axon when microtubules are degraded, causing axonal thinning. Under pharmacological perturbation, atrophy is always retrograde and this is set by a gradient in the microtubule stability. The nature of microtubule depolymerization dictates the type of shape transformation vis à vis beading or retraction. Elucidating the mechanisms of these shape transformations will facilitate development of strategies to prevent or arrest axonal atrophy due to neurodegenerative conditions.
Epithelial cells flows are observed both in vivo and in vitro and are essential for morphogenesis. Here, we show that pulsatile flows involving local contraction and expansion of a tissue can arise in vitro in an epithelial monolayer of Madine Darby Canine Kidney (MDCK) cells. The strength of pulsation can be modulated through friction heterogeneity by observing the monolayer dynamics on micro-contact printed fibronectin grids with dimensions matching the length-scale of spontaneous oscillations. We also report pulsations by inducing wound closure in domains of similar size with micro-fabricated pillars. In contrast, strongly coherent flows can be induced by adding and washing out acto-myosin cytoskeleton inhibitors. To gain insight into the associated cellular mechanisms, we fluorescently label actin and myosin. We find that lamellipodia align with the direction of the flow, and tissue-scale myosin gradients arise during pulsations in wound-healing experiments. Pulsations and flows are recapitulated in silico by a vertex model with cell motility and polarisation dynamics. The nature of collective movements depends on the interplay between velocity alignment and random diffusion of cell polarisation. When they are comparable, a significant pulsatile flow emerges, whereas the tissue undergoes long-range flows when alignment dominates. We conjecture that the interplay between lamellipodial motile activity and cell polarization, with a possible additional role for tissue-scale myosin gradients, is at the origin of the pulsatile nature of the collective flow. Altogether, our study reveals that monolayer dynamics is dictated by simple rules of interaction at cellular levels which could be involved in morphogenesis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.