arXiv subjects

Laurent Chesneau

Publications and source records attributed to Laurent Chesneau.

3 recordsLinked to original sources

arXiv2025

Kinesin-12 KLP-18 contributes to the kinetochore-microtubule poleward flux during the metaphase of C. elegans one-cell embryo

The mitotic spindle partitions chromosomes during cell division by connecting the poles to kinetochores through microtubules (MTs). Their plus-ends, facing the chromosomes, exhibit dynamic instability, which is critical for proper attachment. The poleward flux implicates the displacement of Mts towards the spindle poles, while plus-ends polymerise. It may result from minus-end depolymerisation (treadmilling), sliding by kinesins (e.g., Kinesin-5), or pushing by chromokinesins. Intriguingly, such flux had not been reported in the C. elegans zygote, despite homologs of flux-associated proteins being present. To investigate this, we fluorescently labelled Mts and used photobleaching. We observed no global flux; instead, the bleached zone's edges moved inward. The centrosome-facing front reflected MT dynamic instability, but the chromosome-facing front showed faster recovery, suggesting an additional mechanism. This extra velocity was spatially restricted to the vicinity of chromosomes, suggesting that only the kinetochore Mts may undergo flux. Supporting this, flux required key kinetochore regulators: NDC-80, $\text{CLS-2}^\text{CLASP}$, and $\text{ZYG-9}^\text{XMAP215}$. Flux declined as metaphase progressed, correlating with the attachment maturation from lateral to end-on, and was suppressed by SKA-1 recruitment. Classic treadmilling was unlikely, as most kinetochore MTs in C. $elegans$ do not reach spindle poles. Instead, depleting $\text{KLP-18}^\text{KIF15}$, a kinesin that cross-links and organises Mts during meiosis, reduced front movement. We propose that only kinetochore Mts undergo flux, sliding along the spindle Mts, likely powered by KLP-18. This localised sliding contrasts with global flux seen in other systems, and aligns with observations in human cells showing flux reduction as chromosome-to-pole distance increases.

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arXiv2018

LET-99-dependent spatial restriction of active force generators makes spindle's position robust

During the asymmetric division of the Caenorhabditis elegans nematode zygote, the polarity cues distribution and daughter cell fates depend on the correct positioning of the mitotic spindle, which results from both centering and cortical pulling forces. Revealed by anaphase spindle rocking, these pulling forces are regulated by the force generator dynamics, which are in turn consequent of mitotic progression. We found a novel, additional, regulation of these forces by the spindle position. It controls astral microtubule availability at the cortex, on which the active force generators can pull. Importantly, this positional control relies on the polarity dependent LET-99 cortical band, which restricts or concentrates generators to a posterior crescent. We ascribed this control to the microtubule dynamics at the cortex. Indeed, in mapping the cortical contacts, we found a correlation between the centrosome-cortex distance and the microtubule contact density. In turn, it modulates pulling force generator activity. We modelled this control, predicting and experimentally validating that the posterior crescent extent controlled where the anaphase oscillations started, in addition to mitotic progression. Finally, we propose that spatially restricting force generator to a posterior crescent sets the spindle's final position, reflecting polarity through the LET-99 dependent restriction of force generators to a posterior crescent. This regulation superimposes that of force generator processivity. This novel control confers a low dependence on microtubule and active force generator exact numbers or dynamics, provided that they exceed the threshold needed for posterior displacement. Interestingly, this robustness originates in cell mechanics rather than biochemical networks.

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arXiv2017

Dynein dynamics at the microtubule plus-ends and cortex during division in the C. $\textit{elegans}$ zygote

During asymmetric cell division, dynein generates forces, which position the spindle to reflect polarity and ensure correct daughter cell fates. The transient cortical localization of dynein raises the question of its targeting. We found that it accumulates at the microtubule plus-ends like in budding yeast, indirectly hitch-hiking on $\text{EBP-2}^{\text{EB1}}$ likely via dynactin. Importantly, this mechanism, which modestly accounts for cortical forces, does not transport dynein, which displays the same binding/unbinding dynamics as $\text{EBP-2}^{\text{EB1}}$. At the cortex, dynein tracks can be classified as having either directed or diffusive-like motion. Diffusive-like tracks reveal force-generating dyneins. Their densities are higher on the posterior tip of the embryos, where $\text{GPR-1/2}^{\text{LGN}}$ concentrate, but their durations are symmetric. Since dynein flows to the cortex are non-polarized, we suggest that this posterior enrichment increases dynein binding, thus accounts for the force imbalance reflecting polarity, and supplements the regulation of mitotic progression via the non-polarized detachment rate.

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