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Team Publications
Biomimetism of Cellular Movement
Year of publication 2015
A Chaigne, C Campillo, N S Gov, R Voituriez, C Sykes, M H Verlhac, M E Terret (2015 Jan 20)
A narrow window of cortical tension guides asymmetric spindle positioning in
the mouse oocyte.
Nature communications : 6027 : DOI : 10.1038/ncomms7027
Summary
Cell mechanics control the outcome of cell division. In mitosis, external forces applied on a
stiff cortex direct spindle orientation and morphogenesis. During oocyte meiosis on the
contrary, spindle positioning depends on cortex softening. How changes in cortical
organization induce cortex softening has not yet been addressed. Furthermore, the range of
tension that allows spindle migration remains unknown. Here, using artificial manipulation of
mouse oocyte cortex as well as theoretical modelling, we show that cortical tension has to be
tightly regulated to allow off-center spindle positioning: a too low or too high cortical tension
both lead to unsuccessful spindle migration. We demonstrate that the decrease in cortical
tension required for spindle positioning is fine-tuned by a branched F-actin network that
triggers the delocalization of myosin-II from the cortex, which sheds new light on the
interplay between actin network architecture and cortex tension.
Year of publication 2014
Svitlana Havrylenko, Xavier Mezanges, Ellen Batchelder, Julie Plastino (2014 Nov 11)
Extending the molecular clutch beyond actin-based cell motility.
New journal of physics : DOI : 105012
Summary
Many cell movements occur via polymerization of the actin cytoskeleton beneath the plasma
membrane at the front of the cell, forming a protrusion called a lamellipodium, while myosin
contraction squeezes forward the back of the cell. In what is known as the “molecular clutch”
description of cell motility, forward movement results from the engagement of the actomyosin motor with cell-matrix adhesions, thus transmitting force to the substrate and
producing movement. However during cell translocation, clutch engagement is not perfect,
and as a result, the cytoskeleton slips with respect to the substrate, undergoing backward
(retrograde) flow in the direction of the cell body. Retrograde flow is therefore inversely
proportional to cell speed and depends on adhesion and acto-myosin dynamics. Here we
asked whether the molecular clutch was a general mechanism by measuring motility and
retrograde flow for the Caenorhabditis elegans sperm cell in different adhesive conditions.
These cells move by adhering to the substrate and emitting a dynamic lamellipodium, but
the sperm cell does not contain an acto-myosin cytoskeleton. Instead the lamellipodium is
formed by the assembly of Major Sperm Protein (MSP), which has no biochemical or
structural similarity to actin. We find that these cells display the same molecular clutch
characteristics as acto-myosin containing cells. We further show that retrograde flow is
produced both by cytoskeletal assembly and contractility in these cells. Overall this study
INSTITUT CURIE, 20 rue d’Ulm, 75248 Paris Cedex 05, France | 1
Team Publications
Biomimetism of Cellular Movement
shows that the molecular clutch hypothesis of how polymerization is transduced into motility
via adhesions is a general description of cell movement regardless of the composition of the
cytoskeleton.
Svitlana Havrylenko, Philippe Noguera, Majdouline Abou-Ghali, John Manzi, Fahima Faqir, Audrey
Lamora, Christophe Guérin, Laurent Blanchoin, Julie Plastino (2014 Oct 29)
WAVE binds Ena/VASP for enhanced Arp2/3 complex-based actin assembly.
Molecular biology of the cell : 55-65 : DOI : 10.1091/mbc.E14-07-1200
Summary
The WAVE complex is the main activator of the Arp2/3 complex for actin filament nucleation
and assembly in the lamellipodia of moving cells. Other important players in lamellipodial
protrusion are Ena/VASP proteins, which enhance actin filament elongation. Here we
examine the molecular coordination between the nucleating activity of the Arp2/3 complex
and the elongating activity of Ena/VASP proteins for the formation of actin networks. Using
an in vitro bead motility assay, we show that WAVE directly binds VASP, resulting in an
increase in Arp2/3 complex-based actin assembly. We show that this interaction is important
in vivo as well, for the formation of lamellipodia during the ventral enclosure event of
Caenorhabditis elegans embryogenesis. Ena/VASP’s ability to bind F-actin and profilincomplexed G-actin are important for its effect, whereas Ena/VASP tetramerization is not
necessary. Our data are consistent with the idea that binding of Ena/VASP to WAVE
potentiates Arp2/3 complex activity and lamellipodial actin assembly.
Matthias Bussonnier, Kevin Carvalho, Joël Lemière, Jean-François Joanny, Cécile Sykes, Timo Betz
(2014 Mar 28)
Mechanical detection of a long-range actin network emanating from a
biomimetic cortex.
Biophysical journal : 854-62 : DOI : 10.1016/j.bpj.2014.07.008
Summary
Actin is ubiquitous globular protein that polymerizes into filaments and forms networks that
participate in the force generation of eukaryotic cells. Such forces are used for cell motility,
cytokinesis, and tissue remodeling. Among those actin networks, we focus on the actin
cortex, a dense branched network beneath the plasma membrane that is of particular
importance for the mechanical properties of the cell. Here we reproduce the cellular cortex
by activating actin filament growth on a solid surface. We unveil the existence of a sparse
actin network that emanates from the surface and extends over a distance that is at least 10
times larger than the cortex itself. We call this sparse actin network the “actin cloud” and
characterize its mechanical properties with optical tweezers. We show, both experimentally
and theoretically, that the actin cloud is mechanically relevant and that it should be taken
into account because it can sustain forces as high as several picoNewtons (pN). In particular,
it is known that in plant cells, actin networks similar to the actin cloud have a role in
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Team Publications
Biomimetism of Cellular Movement
positioning the nucleus; in large oocytes, they play a role in driving chromosome movement.
Recent evidence shows that such networks even prevent granule condensation in large cells.
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