In many vimentin-positive cells, intermediate filaments built from the protein vimentin redistribute to the cell cortex during mitosis, forming a framework interwoven with cortical actin whose disruption causes mitotic catastrophes and asymmetric chromosome partitions. The source work (Duarte et al., 2019) established that vimentin's intrinsically disordered C-terminal tail domain — and within it the segment comprising residues 424–448 — is essential for this cortical relocation, and asked how vimentin docks on the actomyosin cortex (direct actin contact, adaptor proteins such as plectin, or membrane-associated factors), what mechanical consequences the cortical vimentin lattice has for cortex contractility, stiffness, rounding, and spindle orientation, which sequence determinants within the 424–448 segment regulate the tail-mediated targeting, how the behavior varies with cell type and co-expressed intermediate filament partners such as nestin, and raised the potential cytotoxic implications of pathophysiological vimentin damage — as observed upon lipoxidation or HIV-protease action — for mitosis, while noting that damage to macromolecules other than vimentin could contribute to these effects. Later work resolved substantial parts of the mechanical and adaptor questions in HeLa cells (plectin-dependent recruitment; cortical tension and confinement effects) and identified a direct but tail-independent vimentin–actin interaction in vitro, leaving the central mechanistic question — what the 424–448 tail segment actually does and how tail-dependent and plectin-dependent recruitment are reconciled — together with the cell-type-dependence and in vivo pathophysiology questions, open.

Background

Vimentin is a type III intermediate filament (IF) protein: a ~466-residue polypeptide with a globular N-terminal head, a conserved central alpha-helical rod that coils into filaments, and a long intrinsically disordered C-terminal tail (residues ~412–466) whose conformation and interactions are still incompletely characterized. IF networks give cells mechanical resilience and interface with the two other cytoskeletal systems, actin filaments and microtubules. The actomyosin cortex is the thin contractile layer of actin filaments and myosin motors beneath the plasma membrane; when animal cells enter mitosis they round up because cortical tension rises, and this rounding is needed for accurate spindle positioning and chromosome segregation. Plectin is a giant cytolinker (crosslinker) protein that binds both actin filaments and IFs and is a well-established mechanical coupler between the two networks. Nestin is a class VI IF protein that co-assembles with vimentin and is associated with vimentin disassembly in mitosis. How vimentin behaves during division was classically described as cell-type dependent — some cells maintain a vimentin cage around the mitotic spindle while others disassemble the network, with disassembly driven by mitotic phosphorylation of vimentin's N-terminal head. Duarte et al. (2019) showed, in several vimentin-positive and vimentin-deficient reconstituted cell models (SW13/cl.2, MCF7, HAP1 VIM knockout, and others), that vimentin filaments and even vimentin particles redistribute to the cell cortex during mitosis, intertwining with cortical actin; that this redistribution requires the disordered tail domain; that serial tail deletions progressively impair cortical association, pinpointing residues 424–448 as critical; and that a tailless mutant forms curly bundles that entangle chromosomes, producing mitotic catastrophes. Disrupting F-actin (but not microtubules) and pathophysiological insults (an HIV protease, lipoxidation at vimentin's single cysteine C328) similarly dislodge vimentin from the cortex. The paper left open the molecular mechanism of the docking, its mechanical consequences, the determinants within the 424–448 segment, the cell-type dependence of the phenomenon, and its in vivo relevance. Subsequent work has clarified part of this picture. Serres et al. (2020) identified vimentin and plectin in a proteomic screen for regulators of the mitotic actin cortex in HeLa cells and showed that vimentin's recruitment to the mitotic cortex is plectin-dependent, that depleting vimentin or plectin thickens the cortex and lowers cortical tension (measured by atomic force microscopy), and that cortical vimentin is required for division under mechanical confinement; phosphomimetic mutation of the N-terminal cyclin-dependent kinase 1 (CDK1, the master mitotic kinase) phosphorylation site Ser56 similarly collapses the cortical vimentin layer. Hou et al. (2025) showed that Aurora B kinase phosphorylates vimentin at Ser73 in the head domain, preventing vimentin bundling and thereby keeping cortical actin uniformly distributed in highly motile cells during prometaphase. On the biochemical side, Wu et al. (2022) demonstrated by super-resolution imaging, cryo-electron tomography, and rheology that vimentin and actin form interpenetrating networks in the interphase cortex with direct, specific associations that enhance contractility and resilience, and Paty et al. (2026) reconstituted a direct interaction in vitro: vimentin binds ATP-actin monomers and stabilizes barbed-end subunits to promote actin elongation and nucleation — an effect that requires neither vimentin's head nor its tail. Petitjean et al. (2024) reconstituted plectin-like actin–vimentin crosslinking in vitro, and Lois-Bermejo et al. (2022) showed that different vimentin tail segments are differentially exposed in cells, including in mitosis, consistent with distinct tail conformations. Together these results establish that vimentin is a genuine physical and functional component of the mitotic cortex and that plectin is one required factor — but the demonstrated direct vimentin–actin contact is tail-independent, so it cannot explain why residues 424–448 of the tail are needed for cortical targeting in mitosis, and no study has identified what that segment binds or which of its residues matter.

Problem Statement

Define the molecular mechanism by which vimentin associates with the actomyosin cortex during mitosis, and determine the functional consequences of that association. Specifically: (1) identify what the vimentin tail segment comprising residues 424–448 contributes to cortical targeting — which protein, lipid, or other interaction this segment mediates, directly or indirectly — and reconcile this tail-segment dependence with the plectin-dependent recruitment demonstrated in HeLa cells and with the recently described tail-independent direct vimentin–actin contact; (2) identify the sequence and structural determinants within this segment, and any post-translational modifications of it, that regulate mitotic cortical association; (3) quantify the consequences of cortical vimentin for mitotic cortex mechanics — cortical tension, stiffness, cell rounding, robustness against deformation, and spindle orientation — across vimentin-positive cell types, including how filament persistence versus disassembly and co-expressed intermediate filament partners such as nestin modulate cortical relocation and its mitotic roles; and (4) establish whether pathophysiological vimentin modifications, such as proteolytic cleavage or lipoxidation, cause mitotic errors in vivo. All four parts are required components of a complete answer: the mechanistic question in part (1) is the central deliverable but does not by itself resolve the task, parts (2)–(4) must each be addressed, and the mechanical characterization of part (3) must cover every quantity listed there — cortical tension, stiffness, cell rounding, robustness against deformation, and spindle orientation — rather than any single one. Where the evidence permits, each part should be settled; where it does not, the answer must state precisely what is established, what remains open, and what evidence would resolve it.

References

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