North Potomac, MD, United States
North Potomac, MD, United States

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Kim J.H.,Center for Cell Dynamics | Cho A.,Center for Cell Dynamics | Yin H.,Center for Cell Dynamics | Schafer D.A.,University of Virginia | And 5 more authors.
Genes and Development | Year: 2011

Dynamic assembly and disassembly of actin filaments is a major driving force for cell movements. Border cells in the Drosophila ovary provide a simple and genetically tractable model to study the mechanisms regulating cell migration. To identify new genes that regulate cell movement in vivo, we screened lethal mutations on chromosome 3R for defects in border cell migration and identified two alleles of the gene psidin (psid). In vitro, purified Psid protein bound F-actin and inhibited the interaction of tropomyosin with F-actin. In vivo, psid mutations exhibited genetic interactions with the genes encoding tropomyosin and cofilin. Border cells overexpressing Psid together with GFP-actin exhibited altered protrusion/retraction dynamics. Psid knockdown in cultured S2 cells reduced, and Psid overexpression enhanced, lamellipodial dynamics. Knockdown of the human homolog of Psid reduced the speed and directionality of migration in wounded MCF10A breast epithelial monolayers, whereas overexpression of the protein increased migration speed and altered protrusion dynamics in EGF-stimulated cells. These results indicate that Psid is an actin regulatory protein that plays a conserved role in protrusion dynamics and cell migration. © 2011 by Cold Spring Harbor Laboratory Press.


Ramel D.,University of Montréal | Wang X.,Center for Cell Dynamics | Wang X.,Toulouse 1 University Capitole | Wang X.,French National Center for Scientific Research | And 3 more authors.
Nature Cell Biology | Year: 2013

Collective cell movements contribute to development and metastasis. The small GTPase Rac is a key regulator of actin dynamics and cell migration but the mechanisms that restrict Rac activation and localization in a group of collectively migrating cells are unknown. Here, we demonstrate that the small GTPases Rab5 and Rab11 regulate Rac activity and polarization during collective cell migration. We use photoactivatable forms of Rac to demonstrate that Rab11 acts on the entire group to ensure that Rac activity is properly restricted to the leading cell through regulation of cell-cell communication. In addition, we show that Rab11 binds to the actin cytoskeleton regulator Moesin and regulates its activation in vivo during migration. Accordingly, reducing the level of Moesin activity also affects cell-cell communication, whereas expressing active Moesin rescues loss of Rab11 function. Our model suggests that Rab11 controls the sensing of the relative levels of Rac activity in a group of cells, leading to the organization of individual cells in a coherent multicellular motile structure. © 2013 Macmillan Publishers Limited. All rights reserved.


Rankin K.E.,University of Washington | Rankin K.E.,Bernhard Nocht Institute for Tropical Medicine | Wordeman L.,University of Washington | Wordeman L.,Center for Cell Dynamics
Journal of Cell Biology | Year: 2010

Astral microtubules (MTs) are known to be important for cleavage furrow induction and spindle positioning, and loss of astral MTs has been reported to increase cortical contractility. To investigate the effect of excess astral MT activity, we depleted the MT depolymerizer mitotic centromere-associated kinesin (MCAK) from HeLa cells to produce ultra-long, astral MTs during mitosis. MCAK depletion promoted dramatic spindle rocking in early anaphase, wherein the entire mitotic spindle oscillated along the spindle axis from one proto-daughter cell to the other, driven by oscillations of cortical nonmuscle myosin II. The effect was phenocopied by taxol treatment. Live imaging revealed that cortical actin partially vacates the polar cortex in favor of the equatorial cortex during anaphase. We propose that this renders the polar actin cortex vulnerable to rupture during normal contractile activity and that long astral MTs enlarge the blebs. Excessively large blebs displace mitotic spindle position by cytoplasmic flow, triggering the oscillations as the blebs resolve. © 2010 Rankin and Wordeman.


Komatsu T.,Center for Cell Dynamics | Kukelyansky I.,Center for Cell Dynamics | McCaffery J.M.,Johns Hopkins University | Ueno T.,Center for Cell Dynamics | And 2 more authors.
Nature Methods | Year: 2010

Using new chemically inducible dimerization probes, we generated a system to rapidly target proteins to individual intracellular organelles. Using this system, we activated Ras GTPase at distinct intracellular locations and induced tethering of membranes from two organelles, endoplasmic reticulum and mitochondria. Innovative techniques to rapidly perturb molecular activities and organelle-organelle communications at precise locations and timing will provide powerful strategies to dissect spatiotemporally complex biological processes. © 2010 Nature America, Inc. All rights reserved.


Guo Q.,Wilmer Eye Institute | Wang X.,Center for Cell Dynamics | Tibbitt M.W.,Howard Hughes Medical Institute | Anseth K.S.,Howard Hughes Medical Institute | And 2 more authors.
Biomaterials | Year: 2012

Synthetic extracellular matrices provide a framework in which cells can be exposed to defined physical and biological cues. However no method exists to manipulate single cells within these matrices. It is desirable to develop such methods in order to understand fundamental principles of cell migration and define conditions that support or inhibit cell movement within these matrices. Here, we present a strategy for manipulating individual mammalian stem cells in defined synthetic hydrogels through selective optical activation of Rac, which is an intracellular signaling protein that plays a key role in cell migration. Photoactivated cell migration in synthetic hydrogels depended on mechanical and biological cues in the biomaterial. Real-time hydrogel photodegradation was employed to create geometrically defined channels and spaces in which cells could be photoactivated to migrate. Cell migration speed was significantly higher in the photo-etched channels and cells could easily change direction of movement compared to the bulk hydrogels. © 2012 Elsevier Ltd.


Wang X.,Center for Cell Dynamics | He L.,Center for Cell Dynamics | Wu Y.I.,University of North Carolina at Chapel Hill | Hahn K.M.,University of North Carolina at Chapel Hill | Montell D.J.,Center for Cell Dynamics
Nature Cell Biology | Year: 2010

The small GTPase Rac induces actin polymerization, membrane ruffling and focal contact formation in cultured single cells1 but can either repress or stimulate motility in epithelial cells depending on the conditions2, 3. The role of Rac in collective epithelial cell movements in vivo, which are important for both morphogenesis and metastasis4-7, is therefore difficult to predict. Recently, photoactivatable analogues of Rac (PARac) have been developed, allowing rapid and reversible activation or inactivation of Rac using light8. In cultured single cells, light-activated Rac leads to focal membrane ruffling, protrusion and migration. Here we show that focal activation of Rac is also sufficient to polarize an entire group of cells in vivo, specifically the border cells of the Drosophila ovary. Moreover, activation or inactivation of Rac in one cell of the cluster caused a dramatic response in the other cells, suggesting that the cells sense direction as a group according to relative levels of Rac activity. Communication between cells of the cluster required Jun amino-terminal kinase (JNK) but not guidance receptor signalling. These studies further show that photoactivatable proteins are effective tools in vivo. © 2010 Macmillan Publishers Limited. All rights reserved.


He L.,Center for Cell Dynamics | Wang X.,Center for Cell Dynamics | Tang H.L.,Center for Cell Dynamics | Montell D.J.,Center for Cell Dynamics
Nature Cell Biology | Year: 2010

Understanding how molecular dynamics leads to cellular behaviours that ultimately sculpt organs and tissues is a major challenge not only in basic developmental biology but also in tissue engineering and regenerative medicine. Here we use live imaging to show that the basal surfaces of Drosophila follicle cells undergo a series of directional, oscillating contractions driven by periodic myosin accumulation on a polarized actin network. Inhibition of the actomyosin contractions or their coupling to extracellular matrix (ECM) blocked elongation of the whole tissue, whereas enhancement of the contractions exaggerated it. Myosin accumulated in a periodic manner before each contraction and was regulated by the small GTPase Rho, its downstream kinase, ROCK, and cytosolic calcium. Disrupting the link between the actin cytoskeleton and the ECM decreased the amplitude and period of the contractions, whereas enhancing cell-ECM adhesion increased them. In contrast, disrupting cell-cell adhesions resulted in loss of the actin network. Our findings reveal a mechanism controlling organ shape and an experimental model for the study of the effects of oscillatory actomyosin activity within a coherent cell sheet. © 2010 Macmillan Publishers Limited. All rights reserved.


He L.,Harvard University | Montell D.,Center for Cell Dynamics
Nature Cell Biology | Year: 2012

How cells sense and respond to physical forces is an area of intense investigation, which poses significant challenges for in vitro experiments and even greater obstacles for in vivo studies. Analyses of integrin complex dynamics in Drosophila melanogaster now provide evidence that altering mechanical force modulates the stability of integrin adhesion in vivo. © 2012 Macmillan Publishers Limited. All rights reserved.


Montell D.J.,Center for Cell Dynamics | Yoon W.H.,Center for Cell Dynamics | Yoon W.H.,Howard Hughes Medical Institute | Starz-Gaiano M.,University of Maryland Baltimore County
Nature Reviews Molecular Cell Biology | Year: 2012

Cell movements are essential for animal development and homeostasis but also contribute to disease. Moving cells typically extend protrusions towards a chemoattractant, adhere to the substrate, contract and detach at the rear. It is less clear how cells that migrate in interconnected groups in vivo coordinate their behaviour and navigate through natural environments. The border cells of the Drosophila melanogaster ovary have emerged as an excellent model for the study of collective cell movement, aided by innovative genetic, live imaging, and photomanipulation techniques. Here we provide an overview of the molecular choreography of border cells and its more general implications. © 2012 Macmillan Publishers Limited. All rights reserved.


He L.,Center for Cell Dynamics | Wang X.,Center for Cell Dynamics | Montell D.J.,Center for Cell Dynamics
Current Opinion in Genetics and Development | Year: 2011

Drosophila oogenesis is a powerful model for the study of numerous questions in cell and developmental biology. In addition to its longstanding value as a genetically tractable model of organogenesis, recently it has emerged as an excellent system in which to combine genetics and live imaging. Rapidly improving ex vivo culture conditions, new fluorescent biosensors and photo-manipulation tools, and advances in microscopy have allowed direct observation in real time of processes such as stem cell self-renewal, collective cell migration, and polarized mRNA and protein transport. In addition, entirely new phenomena have been discovered, including revolution of the follicle within the basement membrane and oscillating assembly and disassembly of myosin on a polarized actin network, both of which contribute to elongating this tissue. This review focuses on recent advances in live-cell imaging techniques and the biological insights gleaned from live imaging of egg chamber development. © 2011 Elsevier Ltd.

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