Acto-myosin network geometry defines centrosome position

Abstract

The centrosome is the main organizer of microtubules and as such, its position is a key determinant of polarized cell functions. As the name says, the default position of the centrosome is considered to be the cell geometrical center. However, the mechanism regulating centrosome positioning is still unclear and often confused with the mechanism regulating the position of the nucleus to which it is linked. Here we used enucleated cells plated on adhesive micropatterns to impose regular and precise geometrical conditions to centrosome-microtubule networks. Although frequently observed there, the equilibrium position of the centrosome is not systematically at the cell geometrical center and can be close to cell edge. Centrosome positioning appears to respond accurately to the architecture and anisotropy of the actin network, which constitutes, rather than cell shape, the actual spatial boundary conditions the microtubule network is sensitive to. We found that the contraction of the actin network defines a peripheral margin, in which microtubules appear bent by compressive forces. The progressive disassembly of the actin network at distance from the cell edges defines an inner zone where actin bundles were absent, where microtubules were more radially organized and where dynein concentration was higher. We further showed that the production of dynein-based forces on microtubules places the centrosome at the center of this zone. In conclusion, the spatial distribution of cell adhesion and the production of contractile forces define the architecture of the actin network with respect to which the centrosome-microtubule network is centered.

Septins Provide Microenvironment Sensing and Cortical Actomyosin Partitioning in Motile Amoeboid T Lymphocytes

“…We suggest that dynein-driven forces within the enhanced MT network produce a substantial compensatory tension for activation of LFA1 during the lack of sufficient actomyosin tension in UR214-9-treated T cells. Indeed, microtubular network is mechanically integrated into the F-actin cytoskeleton via force-generating dyneins (Fokin et al, 2021; Jimenez et al, 2021), forming a singular MT/actomyosin forces transmission system, sharing the same adhesion receptors to govern T cell adhesion and spreading along extracellular cues. In our previous report, we show that dyneins (‘minus’ end-directed microtubule motors) drive the spreading of dendritic protrusions, mediate cell contractility, microtubule bundling and topography-mediated contact guidance in mesenchymal cells (Zhovmer et al, 2021).…”

“…Thus, while UR214-9-treatment may enhance microtubules-dynein contractility-driven T cell transmigration through a single pore, the same stabilized and elongated microtubules may also lead to T cell entanglement and trapping between several adjacent pores ( Figure 6a,e ). Moreover, since force transmission includes mechanical coupling of dyneins and F-actin (Fokin et al, 2021; Jimenez et al, 2021), the loss of cortical actomyosin contractility, caused by either UR214-9 or Blebbistatin treatments may compromise the transmission of dynein-generated forces to the T cell surrounding environment, causing a loss of T cell transmigratory efficiency.…”

The architecture of the actin network can balance the pushing forces produced by growing microtubules

“…Centrosome position is mainly controlled by combinations of pushing and pulling forces produced in the MT network [13][14][15][16][17][18] . Homogeneous distribution of minus-end directed molecular motors, pulling on MTs in the cytoplasm or at the cell cortex, can enforce centrosome centering [19][20][21][22] .…”

“…Actin networks are involved in centrosome positioning and have been proposed to modulate the pushing forces produced by MTs but the underlying mechanisms are obscure 14,18,[28][29][30][31] . There are numerous examples of physical interactions between MTs and actin filaments [32][33][34][35][36][37] .…”

Rapid Prototyping of Organ-on-a-Chip Devices Using Maskless Photolithography

“…For this, we used a commercially available DMD-based system (PRIMO, Alvéole Lab, Paris, France) [38,43,44]. The PRIMO system was used previously for various applications, such as photopatterning of proteins and cells, hydrogel structuration, and fabrication of electron microscopy grids [43][44][45][46][47]. We optimized existing protocols to make it compatible with glass as a substrate for a negative photoresist (SU-8) instead of using silicon wafers, as has been described recently [38].…”