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SUMMARY:Cytoskeleton club Maya Guerri (eq. Le Clainche\, BioCell dpt) and 
 Thennavan Ulaganathan (eq. Charbonnier/Zinn-Justin\, B3S dpt)
DTSTART:20261113T100000Z
DTEND:20261113T120000Z
DTSTAMP:20261112T000800Z
UID:indico-event-483@indico.i2bc.paris-saclay.fr
DESCRIPTION:Maya Guerri (eq. Le Clainche\, BioCell dpt) and Thennavan Ula
 ganathan (eq. Charbonnier/Zinn-Justin\, B3S dpt)\n__________\nSpeaker1: Ma
 ya Guerri \nTitle1: Role of myosin II and α-actinin-1 in the generation 
 of actin contractile bundles\nAbstract1:Many cellular processes rely on th
 e forces produced by the actin protrusive and contractile structures. In n
 on-muscle migrating cells\, contractile stress fibers (SF) responsible for
  pulling the cell body\, are made of anti-parallel actin bundles cross-lin
 ked by α-actinin-1 and are contracted by myosin II motor activity. Recent
  works have highlighted that myosin II is not just a contractile agent but
  it also plays a role in the regulation of actin turnover\, presumably by 
 contributing to the disassembly of the branched actin network forming the 
 lamellipodium at the cell leading edge. However\, it is unclear if myosin 
 II can reorganize those disassembled actin structures into contractile SFs
  or if it even plays a role in the assembly of SFs. Moreover\, if SFs are 
 thought to result either from mDia1-nucleated actin filaments or from the 
 coalescence of pre-existing SFs\, it has been shown that myosin II is invo
 lved in the formation of specific SFs through the reorganization of the ac
 tin cortex. To this aim\, we are using kinetics assays and single-filament
 s observations to study myosin II role in the generation and organization 
 of actin contractile bundles\, as well as the synergy between its motor ac
 tivity and α-actinin-1 cross-linking activity in the reorganization of li
 near and branched actin networks into SFs. We also address this question i
 n structures more similar to lamellipodia through in vitro reconstitution 
 observed in confocal microscopy.\n__________\nSpeaker2: Thennavan Ulagana
 than \nTitle2: Multivalency of KIF2C interactions leads to formation of 
 biomolecular condensates during mitosis\nAbstract2: Mitosis is where a cel
 l undergoes equal division of duplicated chromosomes and ensures transmiss
 ion of the genetic information to the daughter cells. The spindle microtub
 ule attaches to the kinetochore at the centromere of the chromosomes. Succ
 essful bipolar attachment leads to proper chromosomal segregation\; howeve
 r\, errors often happen. These errors are rectified by the KIF2C\, kinesin
 -13 superfamily\, which binds at the plus ends of the microtubule and depo
 lymerise them by inducing the curvature of the protofilaments. Various can
 cer cell lines overexpress KIF2C\, and a recent report from Pao et al. (20
 25) highlights that KIF2C overexpression causes chemoresistance to paclita
 xel. We recently reported the formation of condensates by KIF2C depending 
 on phosphorylation by PLK1. The interactions contributing to condensation 
 are mediated by the folded domain at the N-terminus of KIF2C\, which we te
 rmed as the phospho-barrel (PB) domain. Deletion of PB completely disrupts
  condensation in cells. We identified the potential cellular partners of K
 IF2C by Biotin proximity labelling approach (TurboID) in cells arrested in
  mitosis. Using 1H-15N SOFAST-HSQC NMR and ITC experiments\, we confirmed 
 the direct phospho-dependent binding of the PB domain to several of these 
 partners and determined the binding motif of the PB domain: pT-{P}-X-[IVL]
 . We noticed that KIF2C PB domain binds to several of these motifs in its 
 mitotic partners Sgo2\, CEP170 and CEP170b. We propose that this contribut
 es to the multivalency of the phospho-dependent KIF2C interaction network.
  Moreover\, KIF2C is a dimer. We demonstrated that a construct named NMC c
 ontaining the neck\, motor\, and C-terminal coiled coil domain forms a sta
 ble dimer despite its NTP state: Apo\, AMPPNP\, ATP\, and/or salt conditio
 ns: 150 mM and 300 mM concentrations of NaCl. Next\, we will focus on solv
 ing the structure of this dimer by cryo-electron microscopy to determine t
 he essential amino acids involved in the dimerization. My results suggest 
 that both PB interactions and NMC dimerization contribute to KIF2C condens
 ation in mitosis. The structural insights of the KIF2C will be utilised to
  design specific compounds disrupting condensates and thus counter the che
 moresistance in cancer cells.\n\nhttps://indico.i2bc.paris-saclay.fr/event
 /483/
LOCATION:B26-N2-000 (I2BC CNRS Gif)
URL:https://indico.i2bc.paris-saclay.fr/event/483/
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