![]() ![]() This coupling between curvature and active protrusive forces was explored for a limited regime of parameters in Fošnarič (2019). This coupling was shown theoretically to give rise to positive and negative feedbacks ( Gov, 2018), that can result in pattern formation in both the spatial distribution of the actin nucleators (recruited by the CMCs) and the membrane shape. Nucleators of actin polymerization, such as WAVE, have been associated with curved membrane complexes ( Begemann et al., 2019 Pipathsouk et al., 2021). For the purpose of our model, we do not need to specify the exact molecular components of the CMC, as long as they are curved and that they can also nucleate actin polymerization at the membrane. Bending the membrane can occur due to adsorption of specialized proteins that have a curved shape (such as BAR domain proteins ( Simunovic et al., 2015)), as well as by formation of nanodomains of different lipid composition and polymerization of membrane-bound filaments ( Zimmerberg and Kozlov, 2006 McMahon and Boucrot, 2015 Drab et al., 2023). One mechanism for controlling the spatial pattern of actin polymerization on the membrane, is to couple the actin nucleation to curved membrane components (CMCs), that are both bending locally the membrane and are sensitive to the local membrane curvature. The control of the actin polymerization in space and time is provided by a host of proteins that nucleate actin polymerization where and when it is needed, and are in turn controlled by different signalling cascades. The actin polymerization near the membrane exerts protrusive forces that can give rise to cellular protrusions, such as filopodia and lamellipodia ( Mattila and Lappalainen, 2008). These forces are mostly due to the underlying cytoskeleton, dominated by the cortical actin network. We alter the force model representing the cytoskeleton to simulate the effects of bundled instead of branched structure, resulting in shapes which resemble filopodia.Ĭells in our body have different shapes depending on their function, and they control their shapes by exerting forces on the flexible plasma membrane ( Frey and Idema, 2021). We extend the simulation with curved components of both convex and concave species, where we find the formation of complex ruffled clusters, as well as internalized invaginations that resemble the process of endocytosis and macropinocytosis. It was previously shown that this model can explain the formation of lamellipodia-like flat protrusions, and here we explore the regimes where the model can also give rise to filopodia-like tubular protrusions. We characterize the phase diagrams of this model, as function of the magnitude of the active forces, nearest-neighbor protein interactions and the proteins’ spontaneous curvature. ![]() The cytoskeletal forces describe the protrusive force due to actin polymerization which is recruited to the membrane by the curved protein complexes. We present here further studies and extensions of a minimal physical model, describing a closed vesicle with mobile curved membrane protein complexes. ![]() 6Center for Digital Green-innovation, Nara Institute of Science and Technology, Ikoma, JapanĮukaryotic cells intrinsically change their shape, by changing the composition of their membrane and by restructuring their underlying cytoskeleton. ![]() 5Data Science Center, Nara Institute of Science and Technology, Ikoma, Japan.4Division of Biological Science, Graduate School of Science and Technology, Nara Institute of Science and Technology, Nara, Japan.3Laboratory for Molecular and Cellular Dynamics, RIKEN Center for Biosystems Dynamics Research, Minatojima-minaminachi, Kobe, Hyogo, Japan.2Laboratory of Physics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia.1Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel.Yoav Ravid 1*, Samo Penič 2, Yuko Mimori-Kiyosue 3 †, Shiro Suetsugu 4,5,6, Aleš Iglič 2 and Nir S. ![]()
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