Actin filaments form a size‐dependent diffusion barrier around centrosomes

Abstract

The centrosome, a non-membranous organelle, constrains various soluble molecules locally to execute its functions. As the centrosome is surrounded by various dense components, we hypothesized that it may be bordered by a putative diffusion barrier. After quantitatively measuring the trapping kinetics of soluble proteins of varying size at centrosomes by a chemically inducible diffusion trapping assay, we find that centrosomes are highly accessible to soluble molecules with a Stokes radius of less than 5.8 nm, whereas larger molecules rarely reach centrosomes, indicating the existence of a size-dependent diffusion barrier at centrosomes. The permeability of this barrier is tightly regulated by branched actin filaments outside of centrosomes and it decreases during anaphase when branched actin temporally increases. The actinbased diffusion barrier gates microtubule nucleation by interfering with c-tubulin ring complex recruitment. We propose that actin filaments spatiotemporally constrain protein complexes at centrosomes in a size-dependent manner.

T-cell receptor triggering requires inactivation of Lim kinase-1 by Slingshot-1 phosphatase

“…These data highlight the importance of rapid actin rearrangements not only for proper initial T cell contacts, but also for further reorganisation of the actin and tubulin cytoskeleton in mature immune synapses. For the tubulin cytoskeleton, this may be achieved by requiring actin polymerisation to fix the centrosome at specific locations [52], which could be achieved by the ability of F-actin to organize a diffusion barrier around centrosomes [53], thus favouring the existence of different gradients of regulatory molecules at centrosomal and synaptic sites, as proposed [54]. An interesting model for achieving cell asymmetry at synaptic contacts is based on the ability of T cells to accumulate newly synthesised proteins at specific sites, such as centrosomes, early after TCR activation, without the need for gene expression [54,55].…”

“…For the tubulin cytoskeleton, this may be achieved by requiring actin polymerisation to fix the centrosome at specific locations [52], which could be achieved by the ability of F-actin to organize a diffusion barrier around centrosomes [53], thus favouring the existence of different gradients of regulatory molecules at centrosomal and synaptic sites, as proposed [54]. An interesting model for achieving cell asymmetry at synaptic contacts is based on the ability of T cells to accumulate newly synthesised proteins at specific sites, such as centrosomes, early after TCR activation, without the need for gene expression [54,55]. In this context, the tubulin cytoskeleton is also regulated downstream of Limk1 [56,57], and the precise regulatory pathway for tubulin and actin by SSH1 and its impact on global asymmetric organisation should be investigated.…”

Temporal and anteriorly positioned mitotic zones drive asymmetric microtubule patterns needed for Left-Right Organizer development

“…Centrosome positive and negative microtubule organizing centers (MTOCs) can rely on actin organization for their positioning and function [38][39][40] and in some cases MTOCs have been identified to organize actin 41 . While the centrosome with its associated centrioles traditionally functions as the primary MTOC in most animal cells to organize MTs, our results suggest that KV cells maintain cytokinetic bridge MTs for an alternative structure used during epithelialization.…”

A protein kinase A-regulated centrosomal actin pool sets the threshold for T cell polarization

“…The copyright holder for this preprint this version posted June 3, 2024. ; https://doi.org/10.1101/2024.06.03.597129 doi: bioRxiv preprint suggested. Firstly, it has been shown recently that actin (rather than microtubules) around the centrosome can be a cage that limits the exchange between the cytoplasm and the pericentriolar region (15). A decrease of actin in this area would then weaken this barrier and potentially lead to modification of the centrosomal composition.…”

“…The biological meaning of this threshold is unclear, but it could correspond to the reduction of the size of the actin mesh. Indeed, Cheng et al highlight that centrosomal actin behave as a protein sieve, and that the reduction of its amount allows the centrosome accessibility of proteins with a higher Stockes radius (15). One could then imagine that the 15% reduction is the necessary decrease for recruiting (or loosing) the specific proteins, mentioned above, which are necessary for the T cell morphological change.…”