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Introduction
My lab focuses on uncovering mechanisms of cell division through a multidisciplinary approach that combines cell biology, biophysics (modelling and in silico approaches), systems biology and image processing. See http:://pecreaux.openwetware.org for further info including job offers.
Skills and Expertise
Current institution
Additional affiliations
April 2004 - December 2010
Publications
Publications (69)
Microtubules are key players in cell division. Beyond their dynamic instability, we addressed the role(s) of microtubule flexural rigidity in spindle positioning. We used the nematode Caenorhabditis elegans zygote, which features a unique Doublecortin-family member ZYG-8 DCLK1 , known to regulate microtubule rigidity in neurons. We showed that ZYG-...
Automation of fluorescence microscopy is a challenge for capturing rare or transient events in biology and medicine. It relies on smart devices that integrate and interpret the observed data, and react to the targeted biological event. We report on the Roboscope, a novel autonomous microscope combining sequence interruption and deep learning integr...
How can inter-individual variability be quantified? Measuring many features per experiment raises the question of choosing them to recapitulate high-dimensional data. Tackling this challenge on spindle elongation phenotypes, we showed that only three typical elongation patterns describe spindle elongation in C. elegans one-cell embryo. These archet...
Recent studies have highlighted the significance of the spindle midzone, the region between the segregating chromosomes, in ensuring proper chromosome segregation. By combining 3D electron tomography, cutting-edge light microscopy and a novel single cell in vitro essay allowing single molecule tracking, we have discovered a previously unknown role...
How does inter-individual variability emerge? When measuring a large number of features per experiment/individual, this question becomes non-trivial. One challenge lies in choosing features to recapitulate high-dimension data. In this paper, we focus on spindle elongation phenotype to highlight how a data-driven approach can help. We showed that on...
The microtubule array, assembled into the mitotic spindle, polymerises from the centrosomes and the chromosomes in many organisms. Their plus ends alternate between growing and shrinking. This dynamic instability plays a key role in pulling on the kinetochores to check the spindle assembly and correct the errors in chromosome attachments. In additi...
Artificial intelligence is nowadays used for cell detection and classification in optical microscopy during post-acquisition analysis. The microscopes are now fully automated and next expected to be smart by making acquisition decisions based on the images. It calls for analysing them on the fly. Biology further imposes training on a reduced datase...
In Caenorhabditis elegans zygote, astral microtubules generate forces essential to position the mitotic spindle, by pushing against and pulling from the cortex. Measuring microtubule dynamics there, we revealed the presence of two populations, corresponding to pulling and pushing events. It offers a unique opportunity to study, under physiological...
Artificial intelligence is nowadays used for cell detection and classification in optical microscopy, during post-acquisition analysis. The microscopes are now fully automated and next expected to be smart, to make acquisition decisions based on the images. It calls for analysing them on the fly. Biology further imposes training on a reduced datase...
Fluorescence Lifetime Imaging Microscopy (FLIM) is a robust tool to measure Förster Resonance Energy Transfer (FRET) between two fluorescent proteins, mainly when using genetically-encoded FRET biosensors. It is then possible to monitor biological processes such as kinase activity with a good spatiotemporal resolution and accuracy. Therefore, it is...
In the Caenorhabditis elegans zygote, astral microtubules generate forces, pushing against and pulling from the cell periphery. They are essential to position the mitotic spindle and in turn the cytokinesis furrow, ensuring the proper distribution of fate determinants to the daughter cells. By measuring the dynamics of astral microtubules, we revea...
During asymmetric cell division, the molecular motor dynein generates cortical pulling forces which position the spindle to reflect polarity and adequately distribute cell fate determinants. In Caenorhabditis elegans embryos, despite a measured anteroposterior force imbalance, antibody staining failed to reveal dynein enrichment at the posterior co...
During asymmetric division of the Caenorhabditis elegans zygote, to properly distribute cell fate determinants, the mitotic spindle is asymmetrically localized by a combination of centering and cortical-pulling microtubule-mediated forces, the dynamics of the latter being regulated by mitotic progression. Here, we show a, to our knowledge, novel an...
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...
During asymmetric cell divisions, cortical dyneins generate forces essential to position the spindle after polarity cues, prescribing daughter cells fate. In nematode zygote, cortical dynein pulls on microtubules transiently, raising the question of its targeting and dynamics. Tracking and fluorescence correlation spectroscopy revealed that in the...
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}...
Background: The correct positioning of the mitotic spindle during the asymmetric division of the nematode C. elegans zygote relies on the combination of centering and corticalpulling forces. These forces, revealed by centrosome anaphase oscillations, are regulated through the dynamics of force generators, related to mitosis progression. Recently, w...
Precise positioning of the mitotic spindle is important for specifying the plane of cell division, which in turn determines how the cytoplasmic contents of the mother cell are partitioned into the daughter cells, and how the daughters are positioned within the tissue. During metaphase in the early C. elegans embryo, the spindle is aligned and cente...
Precise positioning of the mitotic spindle is important for specifying the plane of cell division, which in turn determines how the cytoplasmic contents of the mother cell are partitioned into the daughter cells, and how the daughters are positioned within the tissue. During metaphase in the early C. elegans embryo, the spindle is aligned and cente...
3074-Pos. The mitotic spindle ensures correct segregation of sister chromatids and correct partitioning in daughter cells. It comprises dynamical microtubules (alternating polymerizing and depolymerizing), a variety of molecular motors and their regulators. Although spindle structure is well known, the link to its functions remains elusive, calling...
In higher eukaryotes, efficient chromosome congression relies, among other players, on the activity of chromokinesins. Here, we provide a quantitative analysis of kinetochore oscillations and positioning in S. Pombe, a model organism lacking chromokinesins. In wild type cells, chromosomes align during prophase and while oscillating, maintain this a...
E-cadherin (E-cad) is the main component of epithelial junctions in multicellular organisms, where it is essential for cell-cell adhesion. The localisation of E-cad is often strongly polarised in the apico-basal axis. However, the mechanisms required for its polarised distribution are still largely unknown. We performed a systematic RNAi screen in...
How signaling gradients supply positional information in a field of moving cells is an unsolved question in patterning and morphogenesis. Here, we ask how a Wnt signaling gradient regulates the dynamics of a wavefront of cellular change in a flow of cells during somitogenesis. Using time-controlled perturbations of Wnt signaling in the zebrafish em...
During the first embryonic division in Caenorhabditis elegans, the mitotic spindle is pulled toward the posterior pole of the cell and undergoes vigorous transverse oscillations. We identified variations in spindle trajectories by analyzing the outwardly similar one-cell stage embryo of its close relative Caenorhabditis briggsae. Compared with C. e...
Precise positioning of the mitotic spindle is important for specifying the plane of cell division and the subsequent partitioning of the cell's contents to the daughter cells. Studies on different organisms and cell types have suggested diverse centering mechanisms: astral microtubules grow out from the spindle and push against the cortex, cortical...
nmy-2 (RNAi) does not affect spindle positioning and pulling forces. A, Plot of the position of the posterior centrosome along the anterior posterior axis in γ-tub::GFP embryos (left panel), and nmy-2 (RNAi) embryos (right panel). B, Schematic of a laser-cutting experiment. The spindle is cut at anaphase onset with an UV-laser-beam. Velocity of the...
csnk-1 (RNAi) increases the number of invaginations. A, Embryo treated with csnk-1 (RNAi) during centration and rotation of the nuclear centrosome complex. Embryos depleted of CSNK-1 show a stronger formation of invaginations in comparison to embryos treated with nmy-2 (RNAi) (see B), indicating higher forces in csnk-1 (RNAi) during centering and r...
Properties of invaginations in nmy-2 (RNAi). A, Distribution of the maximum length of invaginations. The median length 1.73 µm is indicated by an arrow. Also shown is the distribution of the lifetime of invaginations, the median lifetime 1.77 s is indicated by an arrow. B, Distribution of the average growing and shrinking speed of invaginations. Me...
Properties of invaginations upon a NMY-2 rundown. Box plot of (A) the maximum length, (B) the lifetime, (C) average growing and (D) average shrinking speed of invaginations counted on both anterior and posterior side and obtained upon running down NMY-2. On each box the central mark indicates the median, the edges of the box are the 25th and 75th p...
Localization of PAR-2 and NMY-2 to invaginations. A, First row: micrograph of invaginations obtained after nmy-2 (RNAi) treatment; PAR-2 is labeled with GFP and tubulin with mCherry. Second row: micrograph of invaginations obtained after pfn-1 (RNAi) treatment; PAR-2 is labeled with mCherry and NMY-2 with GFP. Third row: micrograph of invaginations...
Effect of depletion of genes involved in force generation on invaginations. Box plot of the number of invaginations on the anterior (red) and posterior (blue) pole throughout anaphase in all performed double RNAis. For corresponding values, see Table 1. On each box the central mark indicates the median, the edges of the box are the 25th and 75th pe...
Localization of NMY-2 and actin upon cortex weakening. A, Localization of NMY-2::GFP during anaphase and in wild-type embryos (top) and after 24 h of mlc-4 (RNAi) (bottom). Scale bar is 5 µm. B LifeAct::GFP expressing embryo, subjected to f08f8.2 (RNAi) before (top) and after treatment with cytochalasin D (bottom). Scale bar is 5 µm
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Formation of invaginations in an embryo labeled with PAR-2::GFP and PAR-6::cherry after 23 h of nmy-2 (RNAi) treatment. Frames were collected every 20 seconds, the display rate is 10 frames per second (200× real time).
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Formation of invaginations in an embryo labeled with PH::GFP after 23 h of nmy-2 (RNAi) treatment. Frames were collected every 3 seconds, the display rate is 10 frames per second (30× real time).
(0.35 MB MOV)
Formation of invaginations in an embryo labeled with PLCδ-PH::GFP after Cytochalasin D treatment. PH::GFP, f08f8.1(RNAi) embryo was dissected in SGM (Shelton growth medium) and allowed to reach anaphase. The addition of Cytochalasin D during anaphase leads to large numbers if invaginations which can be suppressed by the subsequent addition of Nocod...
Asymmetric positioning of the mitotic spindle in C. elegans embryos is mediated by force-generating complexes that are anchored at the plasma membrane and that pull on microtubules growing out from the spindle poles. Although asymmetric distribution of the force generators is thought to underlie asymmetric positioning of the spindle, the number and...
The first cell division in C. elegans is asymmetric. Asymmetric cell division requires correct positioning of the mitotic spindle. Prior to metaphase, the nuclear-centrosome complex, the precursor of the mitotic spindle, is positioned in the cell center. During anaphase, the spindle is displaced towards the posterior so that bisection of the spindl...
Using videomicroscopy we present measurements of the fluctuation spectrum of giant vesicles containing bacteriorhodopsin pumps. When the pumps are activated, we observe a significant increase of the fluctuations in the low wave vector region, which we interpret as due to a lowering of the effective tension of the membrane.
Active contours is a powerful image segmentation technique based on simultaneously optimizing the overlap of a surface contour with the intensity image (external energy) on the one hand, and a constraining image-independent penalty based on the first and second derivatives of the contour (internal energy) on the other. Although the above form is ap...
oskar mRNA localization to the posterior of the Drosophila oocyte defines where the abdomen and germ cells form in the embryo. Although this localization requires microtubules and the plus end-directed motor, kinesin, its mechanism is controversial and has been proposed to involve active transport to the posterior, diffusion and trapping, or exclus...
The movie shows the movements of GFP-Stau particles and their localization to the posterior pole. The small bright particles are GFP-Stau, whereas the large grey round structures are yolk vesicles that can be also seen by wide-field imaging. In this and all subsequent movies, the posterior pole of the oocyte is to the right. The movie consists of 6...
The movie consists of 120 sequential time points, which are 0.672 s apart played at 20 fps. Magnification: 2000×.
A movie showing GFP-Stau particles in ovaries of females that had been fed with colcemid overnight and 50 min after the inactivation of colcemid with a 10 s UV pulse. GFP-Stau particles undergo fast processive movements after colcemid inactivation and start to accumulate at the posterior pole. Each part of the movie consists of 45 time frames, 0.99...
A magnified area of the oocyte cytoplasm showing two GFP-Stau particles following a similar trajectory. The movie consists of 40 sequential time points, which are 0.477 s apart. Magnification: 4000×.
Two-color timelapse movie to show the colocalization of oskMS2/MS2-GFP and RFP-Stau to the same moving particle. oskMS2/MS2-GFP is in green, RFP-Stau is in red. Due to the sequential imaging of the red and green channels, the two signals do not colocalize completely because of the movement of the particle between images. Twenty-two time frames for...
The right panel shows a temporal merge of successive frames from the movie to reveal oskMS2/MS2-GFP particle tracks. The second half of the movie shows an area of the cytoplasm to show particles that are moving faster than streaming and in the same direction. The movie consists of 120 frames, 0.718 s apart. Magnification 2000×.
A magnified area of the oocyte cytoplasm to show two oskMS2/MS2-GFP particles following a similar trajectory. Some diffusive particles undergoing Brownian movements are also highlighted by colored tracks.
Timelapse movies showing oskMS2/MS2-GFP particle movement in a wild-type oocyte prior to colchicine injection (left) and the same oocyte visualized 15 min after the injection of colchicine (right). Most particles stop moving processively and instead undergo Brownian oscillations. The left movie consists of 93 time frames played at 20 fps. Magnifica...
A movie showing wildtype and Khc27 oocytes side by side played at the same speed (0.6s per frame). oskMS2RNA-MS2GFP does not localise to the posterior in Khc27, and there are few fast particle movements.
Timelapse movie of GFP-Stau particle movements in a wild-type oocyte (left) and a btz2 mutant oocyte (right). Both movies were recorded at 0.478 s per frame.
We present measurements of the fluctuation spectrum of giant vesicles containing bacteriorhodopsin (BR) pumps using video-microscopy. When the pumps are activated, we observe a significant increase of the fluctuations in the low wavevector region, which we interpret as due to a lowering of the effective tension of the membrane.
Asymmetric division of the C. elegans zygote is due to the posterior-directed movement of the mitotic spindle during metaphase and anaphase. During this movement along the anterior-posterior axis, the spindle oscillates transversely. These motions are thought to be driven by a force-generating complex-possibly containing the motor protein cytoplasm...
Automatic segmentation and tracking of biological objects from dynamic microscopy data is of great interest for quantitative biology. A successful framework for this task are active contours, curves that iteratively minimize a cost function, which contains both data-attachment terms and regularization constraints reflecting prior knowledge on the c...
Membrane fusion is an important process in cell biology. While the molecular mechanisms of fusion are actively studied at a very local scale, the consequences of fusion at a larger scale on the shape and stability of the membrane are still not explored. In this Letter, the evolution of the membrane tension during the fusion of positive small unilam...
We have developed a new method of contour analysis using phase contrast microscopy on giant vesicles [1]. Our set-up allows an accurate detection at video rate, and a direct comparison with theory in a planar geometry. We have been able to measure directly fluctuations spectra. For pure lipid vesicles, we measure bending rigidities corresponding to...
In this work, we have investigated a new and general method for the reconstitution of membrane proteins into giant unilamellar vesicles (GUVs). We have analyzed systematically the reconstitution of two radically different membrane proteins, the sarcoplasmic reticulum Ca(2+)-ATPase and the H(+) pump bacteriorhodopsin. In a first step, our method inv...
The fluctuation spectrum of giant unilamellar vesicles is measured using a high-resolution contour detection technique. An analysis at higher q vectors than previously achievable is now possible due to technical improvements of the experimental setup and of the detection algorithm. The global fluctuation spectrum is directly fitted to deduce the me...
A new method of contours analysis has been developed using phase contrast microscopy on giant lipids vesicles. It allows an accurate detection in real time. We obtain fluctuations spectra and we have developed analysis to compare them with theory for planar membranes. Our method was applied to pure lipids vesicles and we obtain good agreement with...
