Biology subjects

Meraldi, P.

Publications and source records attributed to Meraldi, P..

9 recordsLinked to original sources

bioRxiv2026

Coordinated control of both microtubule ends regulates mitotic spindle length

The mitotic spindle is a biomechanical structure whose length must be precisely controlled to ensure faithful chromosome segregation. The treadmilling of microtubules towards centrosomes, termed poleward flux, is involved in spindle length control. However, poleward flux has been shown to be both inversely and directly proportional to spindle length, a contradiction that remains unexplained by current mechanisms. Here we introduce a model which demonstrates that length-dependent regulation at both microtubule ends allows plus- and minus-end dynamics to synchronize with one another, enabling pathways of poleward flux-based spindle length control which can rectify previous results. Moreover, our model predicts that spindle length and poleward flux can vary independently via simultaneous perturbations at both microtubule ends, which we experimentally validate with combinations of KIF18A, KIF2A, and KATNB1 depletions in human cells. Our results thus resolve a longstanding paradox and provide mechanistic insight into the reciprocal control of spindle length and poleward flux.

biophysics↗

bioRxiv2026

Tipping the balance: Synthesis and evaluation of centrinone-based degraders of polo-like kinase 4

Polo-like kinase 4 (PLK4) is a serine/threonine-protein kinase that plays a pivotal role in centriole biogenesis and, as such, represents a master regulator of centriole duplication. Due to its importance in cancer development and progression, PLK4 represents an attractive target for the development of novel therapeutics. Herein, we present a series of molecular degraders of PLK4, based on the highly selective PLK4 inhibitor centrinone, with the aim of targeting PLK4 for degradation via the ubiquitin-proteasome system. While all synthesized degraders retained low nanomolar binding affinities to the kinase domain of PLK4, large differences were found with respect to their ability to change cellular PLK4 levels. We uncover a complex pharmacological profile of the most potent degraders, D6 and D10, consisting of concomitant lowering of PLK4 levels through degradation, and enhancing PLK4 levels through inhibition of its autoregulation - dependent on its localization at the centrioles.

cell biology↗

bioRxiv2025

Bora, CEP192 and Cenexin activate different Plk1 pools and regulate distinct cell and centrosome cycle transitions

Polo-like kinase 1 (Plk1) regulates multiple steps of the cell and centrosome cycle, including mitotic entry, DNA-damage recovery, centrosome maturation and centriole disengagement. Plk1 activity depends on several independent cofactors, such as the cytoplasmic Bora, and the centrosomal proteins Cep192 and Cenexin. However, whether these Plk1 coactivators differentially regulate the Plk1-dependent processes is unknown. Here, we show that each Plk1 coactivator controls different cell cycle steps via distinct Plk1 pools in human cells. While Bora is the main driver for mitotic entry, DNA-damage recovery and centrosome maturation, centriole disengagement is mainly regulated by Cep192 and Cenexin. Moreover, we find that Plk1 and Cep192 drive S-phase progression by promoting replication origin firing. Our results thus uncover the complexity of the Plk1 activation regulatory network, in which distinct upstream activators dictate its activity in a context-dependent manner.

cell biology↗

bioRxiv2024

Transient lagging chromosomes cause primary microcephaly

Primary microcephaly results from the impaired neuronal progenitor proliferation, causing reduced brain size and impaired cognitive abilities. Loss of the most frequently microcephaly genes, WDR62 and ASPM, slows down poleward microtubule flux and results in transient lagging chromosomes in anaphase. Whether these defects cause primary microcephaly is unknown. Here we show that transient lagging chromosomes elicit an Aurora-B-dependent activation of 53BP1 and p21, impairing cell proliferation. Co-depletion of the microtubule depolymerase inhibitor CAMSAP1/Patronin in a WDR62 depletion background, restores normal flux rates, suppresses lagging chromosomes, and allows normal cell proliferation in human cells, while rescuing the small brain and the cognitive defects in fly larvae. We postulate that transient lagging chromosomes in anaphase and 53BP1/p21-dependent response they elicit, are a major driver of primary microcephaly.

cell biology↗

bioRxiv2023

Centrosome age breaks spindle size symmetry even in symmetrically dividing cells

Centrosomes are the main microtubule organizing center in animal cells. Due to the semi-conservative nature of centrosome duplication, the two centrosomes differ in age. In asymmetric stem cell divisions, centrosome age can induce an asymmetry in half-spindle lengths. However, whether centrosome age affects the symmetry of the two half-spindles in tissue culture cells thought to divide symmetrically, is unknown. Here, we show that in human epithelial and fibroblastic cell lines centrosome age imposes a subtle spindle asymmetry that leads to asymmetric cell daughter sizes. At the mechanistic level, we show that this asymmetry depends on the preferential accumulation on old centrosomes of the microtubule nucleation-organizing proteins pericentrin, {gamma}-tubulin, Cdk5Rap2, and TPX2, under the control of a cenexin-bound pool of the mitotic kinase Plk1. Moreover, we find that old centrosomes have a higher microtubule nucleation capacity. We therefore postulate that centrosome age breaks spindle size symmetry via microtubule nucleation even in cells thought to divide symmetrically.

cell biology↗

bioRxiv2022

Mild replication stress causes premature centriole disengagement via a sub-critical Plk1 activity under the control of ATR-Chk1

A tight synchrony between the DNA and centrosome cycle is essential for genomic integrity. Centriole disengagement, which licenses centrosomes for duplication, occurs normally during mitotic exit. We recently demonstrated that mild DNA replication stress in untransformed human cells causes premature centriole disengagement at mitotic entry, leading to transient multipolar spindles that favour chromosome mis-segregation. How mild replication stress accelerate the centrosome cycle at the molecular level remained, however, unclear. Using expansion microscopy, we show that mild replication stress already induces premature centriole disengagement in G2 via the ATR-Chk1 axis of the DNA damage repair pathway. We demonstrate that this results in a subcritical Plk1 kinase activity that is insufficient for rapid mitotic entry. Nevertheless, it primes the pericentriolar matrix for Separase-dependent disassembly causing premature centriole disengagement in G2. We postulate that the differential requirement of Plk1 activity in the DNA and centrosome cycles explains how mild replication stress disrupts the synchrony between both processes and contributes to genomic instability.

cell biology↗

bioRxiv2021

Microtubule-based mitotic spindles contain a micron-sized mixed-nucleotide zone

Current models infer that the microtubule-based mitotic spindle is built from GDP-tubulin with small GTP caps at microtubule plus-ends, including those that attach to kinetochores (K-fibres). Here we reveal that K-fibres additionally contain a dynamic mixed-nucleotide zone that reaches several microns in length. This zone becomes visible in cells expressing fluorescently labelled EBs, a known marker for GTP-tubulin, and endogenously-labelled HURP - a protein which we show to preferentially bind the GDP microtubule lattice in vitro. In living cells HURP accumulates on the ends of depolymerising K-fibres, whilst avoiding recruitment to nascent polymerising K-fibres. This gives rise to a growing "HURP-gap" which we can recapitulate in a minimal computational simulation. We therefore postulate that the K-fibre lattice contains a dynamic, micron-sized mixed-nucleotide zone. One Sentence SummaryWe reveal that the microtubules of the mitotic spindle contain a third, uncharacterized domain, a mixed nucleotide zone that resides between the GTP-cap and the GDP-tubulin lattice.

cell biology↗

bioRxiv2021

PLK1 controls centriole distal appendage formation and centrobin removal via independent pathways

Centrioles are central structural elements of centrosomes and cilia. They originate as daughter centrioles from existing centrioles in S-phase and reach their full functionality with the formation of distal and subdistal appendages two mitoses later. Current models postulate that the centriolar protein centrobin acts as placeholder for distal appendage proteins that must be removed to complete distal appendage formation. Here, we investigated in non-transformed human epithelial cells the mechanisms controlling centrobin removal and its effect on distal appendage formation. We demonstrate that centrobin is removed from older centrioles due to a higher affinity for the newly born daughter centrioles, under the control of the centrosomal kinase Plk1. Centrobin removal also depends on the presence of subdistal appendage proteins on the oldest centriole. It is, however, not required for distal appendage formation even though this process is equally dependent on Plk1. We conclude that during centriole maturation, Plk1 kinase regulates centrobin removal and distal appendage formation via separate pathways.

cell biology↗

bioRxiv2019

Centrosomes control kinetochore-fiber plus-end dynamics via HURP to ensure symmetric divisions

During mitosis centrosomes can affect the length of kinetochore-fibers (k-fibers) and the stability of kinetochore-microtubule attachments, implying that they regulate k-fiber dynamics. The exact cellular and molecular mechanisms by which centrosomes regulate k-fibers remain, however, unknown. Here, we created human non-cancerous cells with only one centrosome to investigate these mechanisms. Such cells formed highly asymmetric bipolar spindles that resulted in asymmetric cell divisions. K-fibers in acentrosomal spindles were shorter, more stable, had a reduced poleward microtubule flux at minus-ends, and more frequent pausing events at their plus-ends. This indicates that centrosomes regulate k-fiber dynamics both locally at minus-ends and far away at plus-ends. At the molecular level we find that the microtubule-stabilizing protein HURP is enriched on the k-fiber plus-ends in the acentrosomal spindles of cells with only one centrosome. HURP depletion rebalance k-fiber stability and dynamics in such cells, and improved spindle and cell division symmetry. Our data further indicate that HURP accumulates on k-fibers inversely proportionally to half-spindle length. We propose that centrosomes regulate k-fiber plus-ends indirectly via length-dependent accumulation of HURP. Thus by ensuring equal k-fiber length, centrosomes promote HURP symmetry, reinforcing the symmetry of the mitotic spindle and of cell division.

cell biology↗