Pecreaux

Team: "Reverse Engineering Cell Division" (CeDRE) Home Contact [| Members ] Publications [| Official Web ]

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Research Interests

Interactions of molecular motors, cytoskeletal filaments and their regulators drive cell division’s complex choreography. We assert that physics and mechanics play not only an essential role in explaining players’ molecular action, but also in signaling and regulation. In the long term, we aim to contribute by providing a novel paradigm of cell division physics and mechanics linking molecular details to cell-level events.

Introduction

In nematode ‘’Caenorhabditis elegans’’ one-cell embryo, prior to asymmetric division, the mitotic spindle is centered. It is maintained in cell center during early mitosis, until anaphase onset, when it is posteriorly displaced by cortical force generators pulling on astral microtubules and concurrently undergoes transverse oscillations.

We have hypothesized that cell division’s diversity of events and stereotypic choreography can be modeled including only internal-spindle, centering, and cortical forces on the macroscopic level and that this model can be based on experimental molecular characteristics and interactions of players/proteins, on the microscopic level.

Some recent research

Previous modeling of anaphase spindle rocking and posterior displacement suggests a mechanism relying on dynamics of cortical force generators, likely cytoplasmic dyneins [Pecreaux et al. 2006]. M. Delattre and her lab (LBMC, ENS Lyon, France) observed sticking similarities of spindle motion between various species of the ‘’Caenorhabditis’’ genus and subtle but intriguing differences. We collaborated with her lab to account for differences between C. ‘’elegans’’ and C. ‘’briggsae’’ and we demonstrated the existence of a ‘’’positional switch’’’ controlling cortical pulling forces exerted on the posterior centrosome [Riche et al. 2013].

We proposed that the dynamics of astral microtubule is the mechanism causing such a switch and successfully modeled it in 3D. Through optimized fluorescence microscopy of labelled microtubules and advanced image processing, we have created a spatial map of microtubule cortical contact and validated the model. This mechanism creates robustness to evolution of essential proteins as G-protein regulator, to ensure a robust final position of the spindle through a mechanical network, in the sense of systems biology.

We were also interested in the mechanism that maintain the spindle in cell center during metaphase. Previously, was developed a fine tracking of spindle motion and micro-movements analysis to characterize centering [Pecreaux et al. 2006]. Our results suggest that cortical force generators play no role in spindle maintaining at cell center during metaphase despite the large size of C. elegans embryo (length of AP axis of about 55 µm and transverse axes of 30 µm).

In the lab, we hypothesized that such a centering could be achieved through astral microtubules pushing against the cortex and we investigated the molecular mechanism though a mini-screen of putatively involved proteins. Analysis of microtubule dynamics supplement this approach to build a consistent model of centering.

A pool of dynein, found in the cell cortex, is thought to pull on the astral microtubules to generate forces causing spindle posterior displacement and rocking. We imaged live fluorescently labeled dynein intermediated light chain DYCI-1 and tracked it by advance image processing to uncover the motion of dynein spots. We found that the dynein is accumulated at the growing end of the astral microtubules and transported to the cortex, in an EBP-2 (C. ‘’elegans’’ EB-1 homolog) dependent manner, suggesting a Hitchhiking mechanism.

Approach

To achieve such research, our team is multidisciplinary including:

Biophysical modeling

featuring a systems approach to understand collective behaviors of the players and robustness to noise; this will enable me to distinguish the dominant mechanisms.

Validation by in vivo quantitative experiments

using mainly partial RNA interference, in which the continuous depletion of a protein corresponds to parameter variation in the biophysical model;

Advanced image processing and experimental physics quantification

to ensure a detailed comparison to the model’s predictions.

Such an “experimental systems biophysics” approach, by reconciling micro- and macro-scopic scales, can provide novel perspectives in understanding biological phenomena, complementing molecular cell biology approaches, and in vitro or theoretical studies. It is particularly suitable at highlighting collective behaviors involving multiple players (proteins) to create robust cell division, able to compensate for changes in genes or environment for example.