November 19, 2014

You might not be able to get rid of the bad guys, but you can still win the battle if you cripple their mobility. Today’s image is from a paper describing how a tumor’s microenvironment can predict the motility of individual tumor cells.

Metastasis is the spread of cancer cells throughout the body. The motility of tumor cells depends on the microenvironment around them, and a recent paper systematically looks at how that microenvironment can predict or alter the behavior of tumor cells. Gligorijevic and colleagues tracked the motility of individual mouse mammary carcinoma cells in vivo using high-resolution multi-photon microscopy, and found that tumor cells exhibited either fast or slow locomotion. Those tumor cells with slow locomotion also exhibited invadopodia, protrusions that Gligorijevic and colleagues directly link to degradation of the underlying extracellular matrix and metastasis. While no single parameter of the tumor’s microenvironment could predict the locomotion of tumor cells, a support vector machine algorithm indicated how combinations of many parameters could predict tumor cell phenotype and behavior. By characterizing the heterogeneous microenvironment of a tumor and predicting the location and behavior of metastatic tumor cells, researchers can better understand treatment of tumors and the varying responses. Images above show protrusions (arrowheads, over 30 minutes) on two different tumor cells with slow locomotion, with protrusions facing collagen fibers (purple).

BONUS!! Check out a movie of these protrusions below. Note that some protrusion face collagen fibers (purple, panels a and b), and some protrude into blood vessels (red, panels c and d).

BONUS!! Check out Bojana Gligorijevic ‘s interview with SciArt about her images, research, and art here.

Gligorijevic, B., Bergman, A., & Condeelis, J. (2014). Multiparametric Classification Links Tumor Microenvironments with Tumor Cell Phenotype PLoS Biology, 12 (11) DOI: 10.1371/journal.pbio.1001995

September 17, 2014

All good things must end—even the focal adhesions that are so key to cell migration. Today’s notable image is the first live cell visualization of ECM degradation at focal adhesions, in a recent paper that reports the link between CLASPs, exocytosis, and focal adhesion turnover. 

Cell migration depends on the precisely-timed formation of focal adhesions (FAs) that link the crawling cell to the extracellular matrix (ECM). FAs serve as anchor points for the crawling cell, yet must later disassemble in order to allow continued movement of the cell. A recent paper describes how CLASP proteins link FA-associated microtubules, exocytosis, and FA turnover. CLASP proteins are +TIP proteins, which means that they are found on the growing ends of microtubules. Stehbens and colleagues found that the clustering of CLASPs around FAs correlates with the timing of FA disassembly, and that CLASPs are required for ECM degradation. Stehbens and colleagues also found that the tethering of microtubules to FAs, via CLASPs, serve as a transport pathway for exocytic vesicles at FAs. The images above are the first live cell images of ECM degradation (visualized as dark regions, top panel) at FAs (magenta).

BONUS! For more information on the scanning angle interference microscopy used in this paper, check out Matthew Paszek’s Nature Methods paper here.

Stehbens, S., Paszek, M., Pemble, H., Ettinger, A., Gierke, S., & Wittmann, T. (2014). CLASPs link focal-adhesion-associated microtubule capture to localized exocytosis and adhesion site turnover Nature Cell Biology, 16 (6), 561-573 DOI: 10.1038/ncb2975
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

July 31, 2014

Do you ever feel nostalgic for a specific paper? Maybe this paper inspired your own research, or maybe it was a paper you immediately knew would be game-changing. Maybe, like today’s TBT paper, it was a great paper about solidly executed research with a memorable giggle-inducing technique. Thanks to a nostalgic HighMag reader and friend, Omar Quintero, we are being re-introduced to gonad sandwiches. 

In mammals, sex determination refers to the changes during early development that lead to the formation of either the testis or ovary. A gene on the Y chromosome called Sry initiates testis formation from the early bipotential gonad, including organizing Sertoli cells into the testis cord structure. In a 1997 paper, Martineau and colleagues investigated the early cell movements that occur after Sry expression, specifically the movement of nearby mesonephric cells to the genital ridge. To see these cell movements, Martineau and colleagues grafted a “blue” mesonephros from a mouse ubiquitously expressing β-galactosidase next to a “white” gonad from a different mouse. The movement of blue cells into the white gonad in these gonad sandwiches revealed that this movement is dependent on a signal induced by the male (XY) gonad that acts as a chemoattractant. Migration does not occur if an XX gonad is used in the sandwich, yet migration can occur whether an XY or XX mesonophros is used. The images above show the different XX and XY combinations used in these experiments, with XY gonads leading to extensive migration of blue cells. 

Martineau, J., Nordqvist, K., Tilmann, C., Lovell-Badge, R., & Capel, B. (1997). Male-specific cell migration into the developing gonad Current Biology, 7 (12), 958-968 DOI: 10.1016/S0960-9822(06)00415-5

Copyright ©1997 Elsevier Ltd. All rights reserved.

April 24, 2014

I’m still waiting for my miniaturizing spaceship* so I can dive into a cell with my dog and ride in the lamella of a crawling cell. Until then, I will gladly enjoy images like today’s, from the Lippincott-Schwartz lab.

A cell’s shape can change for many reasons, including crawling, tissue regeneration, and cancer progression. Cell shape is dynamic, relying on temporal and spatial coordination of several processes. The three-dimensional nature of cell shape, however, presents a challenge for microscopists. By using structured illumination microscopy (SIM), Burnette and colleagues created images of the three-dimensional organization of actin filaments. From these 3D superresolution analyses in crawling cells, Burnette and colleagues found a contractile network of actin filaments at the top of a crawling cell, organized like muscle sarcomeres. Their model of balanced contraction and adhesion helps to guide further investigations of cell shape changes in healthy and diseased tissue. The image above shows actin filaments at color-coded heights within a crawling cell. The closed arrow points to actin at the top of the cell.

*My birthday is next month, if anyone is wondering about gift ideas.  

Burnette, D., Shao, L., Ott, C., Pasapera, A., Fischer, R., Baird, M., Der Loughian, C., Delanoe-Ayari, H., Paszek, M., Davidson, M., Betzig, E., & Lippincott-Schwartz, J. (2014). A contractile and counterbalancing adhesion system controls the 3D shape of crawling cells originally published in the Journal of Cell Biology, 205 (1), 83-96 DOI: 10.1083/jcb.201311104

March 19, 2014

Migration fingers are the spirit fingers of a migrating epithelial sheet of cells. Woowoo!! Today’s image is from a cool paper on the forces exerted by a migration finger, so naturally I’m showing my enthusiasm with my own spirit fingers.

Cells can migrate on their own or as part of an epithelial sheet of many cells. Collective migration features the forward movement of multicellular migration fingers, and can be seen throughout development, in spreading tumors and in healing wounds. The formation of each migration finger begins with the transformation of a single cell into a leader cell. A recent paper looks at leader cells and migration fingers, specifically the biochemical mechanisms involved and the generation of forces exerted by migration fingers. Reffay and colleagues monitored the traction forces exerted by a migration finger, and found that the leader cell exerts a large mechanical force that drags its followers with the help of the small GTPase RhoA. In the images above, the contractile acto-myosin cable that runs the length of the migration finger is cut by laser photoablation (arrow, middle). A new leader cell is formed at the site of the cut (asterisk, right), suggestion that the cable serves to prevent the formation of new leader cells, which in turn allows the formation of long migration fingers.


Reffay, M., Parrini, M., Cochet-Escartin, O., Ladoux, B., Buguin, A., Coscoy, S., Amblard, F., Camonis, J., & Silberzan, P. (2014). Interplay of RhoA and mechanical forces in collective cell migration driven by leader cells Nature Cell Biology, 16 (3), 217-223 DOI: 10.1038/ncb2917
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

January 22, 2014

The C-word is a dirty, dirty word that every single person dreads hearing. Cancer touches every family at some point (or so it seems), so the effort put forth to finding a “cure” for cancer is huge. Today’s image is from a very exciting paper that shows how specific cells in a breast tumor lead the charge towards invasion. 

The spread of cancer, or metastasis, can occur either through the invasion of single tumor cells into nearby tissue or by collective invasion of several cells as a cohesive unit. A recent paper from Andy Ewald’s lab at Johns Hopkins describes the identification of cells involved in collective invasion, using a 3D assay of primary breast tumors invading other tissue. Kevin Cheung and colleagues found that in mouse breast cancer models and diverse human breast tumors, the cells leading the invasion charge are distinct from the bulk tumor cells, and express the basal epithelial genes cytokeratin-14 (K14) and p63. Additionally, knockdown of either K14 or p63 could block collective invasion in advanced carcinomas. In the images above, leading invasive cells express K14 (middle image, green) and are distinct from the bulk of the mouse mammary tumor.

BONUS!! For a great “Out of the Box” description of these very cool results, click here.

Kevin J. Cheung, Edward Gabrielson, Zena Werb, Andrew J. Ewald (2013).  Collective Invasion in Breast Cancer Requires a Conserved Basal Epithelial Program.  Cell, 15 (7), 1639–1651. http://dx.doi.org/10.1016/j.cell.2013.11.029  Copyright ©2013 Elsevier Ltd. All rights reserved.

July 17, 2013

We don’t need to reinvent the wheel (even if someone tried to in 2001...click here).  We use the wheel for so many things ranging from transport to energy.  Cells have proven clever at co-opting machinery for multiple processes, as the paper from today’s image describes.  This recent paper shows the use of specific machinery in both cytokinesis and neuronal migration.

When neurons migrate, there is a leading process in the front of the cell body and a trailing process.  The leading process contains actin filaments that enable the cell body of the neuron to move forward.  A recent paper describes how the microtubule-based motor kinesin-6 plays an important role in neuronal migration.  Kinesin-6 is best known for its role in cytokinesis, the physical division of a cell after mitosis.  Falnikar and colleagues found that kinesin-6 concentrates in the same region as actin filaments in the leading process of a migrating neuron.  Without kinesin-6, neurons lose their bipolar leading-trailing process morphology, concentrate actin filaments in more than one process, and either remain stationary or continually change the direction of migration.  In addition, Falnikar and colleagues found that kinesin-6 signals through the GTPase activating protein MgcRacGAP to regulate the actin cytoskeleton, as it does during cytokinesis.  In the images above, control neurons (top time-lapse series) moved in a single direction, while neurons depleted of kinesin-6 bottom) frequently changed directions.

BONUS!!  Check out a movie of a wandering, migrating kinesin-6-depleted neuron below.

Aditi Falnikar, Shubha Tole, Mei Liu, Judy S. Liu, & Peter W. Baas (2013). Polarity in Migrating Neurons Is Related to a Mechanism Analogous to Cytokinesis Current Biology, 23 (13), 1215-1220 DOI: 10.1016/j.cub.2013.05.027 Copyright ©2013 Elsevier Ltd. All rights reserved.

July 10, 2013

The grace of a migrating cell is as deceiving as a pair of Spanx on an English Bulldog… there is a lot going underneath.  Today’s image is from a paper showing the importance of the protein vinculin at the leading edge of a migrating cell.

Cell migration is driven by actin filament polymerization that pushes the leading edge of the cell forward, as well as F-actin retrograde flow.  Focal adhesions (FAs) adhere the crawling cell to the underlying extracellular matrix (ECM), and are assembled and disassembled near the leading edge of the cell.  Proteins of these FAs are believed to make up a “molecular clutch” that engages the retrograde F-actin flow, and a recent paper identifies the protein vinculin, an actin-binding protein, as a molecular clutch.  Thievessen and colleagues investigated the effects of vinculin gene disruption in migrating fibroblasts, and found that vinculin is important in regulating F-actin organization and FA dynamics.  Specifically, vinculin generates the ECM traction forces necessary for migration, and promotes FA formation and turnover.  In the images above, a normal fibroblast (top) and a fibroblast lacking vinculin (bottom) show F-actin (green) and the lamellipodial protein cortactin (purple).  Normal crawling fibroblasts have a sharply defined band of cortactin colocalized with F-actin at the leading edge, while vinculin mutants have a wider, less defined region of cortactin at the leading edge, suggesting the importance of vinculin in leading edge organization.

BONUS!  Check out some cool movies from this paper here.

Thievessen I, Thompson PM, Berlemont S, Plevock KM, Plotnikov SV, Zemljic-Harpf A, Ross RS, Davidson MW, Danuser G, Campbell SL, & Waterman CM (2013). Vinculin-actin interaction couples actin retrograde flow to focal adhesions, but is dispensable for focal adhesion growth. originally published in the Journal of Cell Biology, 202 (1), 163-77 PMID: 23836933

June 18, 2013

The study of how cells move in development is not just about development.  Understanding cell migration can also help researchers understand how tumors spread and invade other tissues.  So, the next time you see someone roll their eyes at your fruit fly egg chambers (or worm vulva, or culture dishes), take pity at their ignorance and explain to them how they should thank you instead.

The movement of cells during development drives the shape changes and organization of an embryo.  In the fruit fly ovary, a small cluster of border cells migrates across a region of the egg chamber in order to reach the oocyte.  This collective migration of these border cells depends on polarization of the actin cytoskeleton.  A recent paper describes the role of the Hippo signaling pathway in driving the polarization of actin to the outer rim of the migrating border cell cluster.  Lucas and colleagues found that upstream Hippo pathway components localize to the contacts between border cells within the cluster in order to link polarity signaling with actin cytoskeleton organization.  In the images above, the actin cytoskeleton (red) can be seen at the outer rim of the migrating cluster of border cells (arrows) as it moves across the egg chamber towards the oocyte (top to bottom, chronologically).  Higher magnification views of the cluster are on the right.

 Lucas, E., Khanal, I., Gaspar, P., Fletcher, G., Polesello, C., Tapon, N., & Thompson, B. (2013). The Hippo pathway polarizes the actin cytoskeleton during collective migration of Drosophila border cells originally published in the Journal of Cell Biology, 201 (6), 875-885 DOI: 10.1083/jcb.201210073

February 7, 2013

The alphabet soup of cell biology can be overwhelming, but APC is one jumble of letters that most cell biologists are very familiar with.  APC is a protein that functions in cell division and development, and is the most commonly mutated gene in colon cancer.  Today’s image is from a paper describing another hat that APC gets to wear—a role in the interaction between microtubules and intermediate filaments.

Intermediate filaments (IFs) and microtubules are both part of the cell’s cytoskeleton, and their interactions together during different cellular processes have brought attention to the possible proteins that guide these interactions.  IFs function in cell migration, and a recent paper describes rearrangements of the IF network during the migration of astrocytes, cells that provide nutritional and structural support for neurons in the brain.  Sakamoto and colleagues found that the tumor suppressor protein APC (adenomatous polyposis coli) is required for microtubule-IF interactions and for the microtubule-based rearrangements of the IF network in migrating astrocytes.  Loss of APC resulted in a disorganized IF network in glioma and carcinoma cells.  The images above show microtubule-APC-IF interactions in a migrating astrocyte, with fluorescently labeled IFs (vimentin, green), APC (red), and microtubules (blue).  Arrowheads point to APC along microtubules, while arrows point to both IFs and APC along microtubules.

Sakamoto, Y., Boeda, B., & Etienne-Manneville, S. (2013). APC binds intermediate filaments and is required for their reorganization during cell migration originally published in the Journal of Cell Biology, 200 (3), 249-258 DOI: 10.1083/jcb.201206010

January 7, 2013

Happy New Year! To kick off 2013 properly, today I’m featuring an image from a lab whose leader is one of the coolest cats in cell biology (click here for proof). The image is from a paper describing the nanoscale forces within individual focal adhesions, and how these forces guide cell migration.

“Durotaxis” is the directed cell migration along a rigidity gradient—meaning the migration toward a more mechanically stiff extracellular matrix (ECM). Durotaxis occurs throughout development and cancer metastasis, two situations during which the stiffness of a tissue can vary locally or over time. A recent paper describes how cells sample the environment to sense ECM stiffness, and how this sampling guides migration of a cell toward stiff ECM. Using high-resolution time-lapse traction force microscopy, Plotnikov and colleagues documented the forces within individual focal adhesions (FAs) in migrating cells. These individual FAs tug on the ECM to function as local sensors of ECM rigidity. This tugging traction is necessary for durotaxis, but not chemotaxis, another type of cell migration. In the images above, paxillin is fluorescently labeled to show FAs (top, left and zoomed image on right). The corresponding heatmaps (bottom, left and right) show the magnitudes of tugging forces on the ECM (FAs outlined in black), while the stress vector field image (middle right) shows the direction of the forces within the FAs.

Plotnikov, S., Pasapera, A., Sabass, B., & Waterman, C. (2012). Force Fluctuations within Focal Adhesions Mediate ECM-Rigidity Sensing to Guide Directed Cell Migration Cell, 151 (7), 1513-1527 DOI: 10.1016/j.cell.2012.11.034

Copyright ©2013 Elsevier Ltd. All rights reserved. 

December 17, 2012

Today’s image is from a paper on the development of the zebrafish eye lens. As I look at the paper’s stunning images, I’m sure that these cute little eyes are following me around my room.

The eye lens is composed of two cell types called lens epithelial cells and lens fibers. During development of the eye, lens fibers are generated from dividing lens epithelial cells, and later undergo morphogenesis. During morphogenesis, these new lens fibers elongate and then migrate toward the midline of lens, with newer lens fibers displacing and compacting older fiber layers as the entire lens grows. A recent paper investigates the relationship between morphogenesis and cell interactions with the underlying extracellular matrix (ECM). Hayes and colleagues found that fibronectin1 (Fn1), an ECM component, and integrin α5, the Fn1 cellular binding partner, are both required for lens fiber morphogenesis in developing zebrafish. Mutations in either gene cause defects in lens fiber adhesion, elongation, and packing, in turn leading to cataracts. Hayes and colleagues suggest that lens fibers migrate along an Fn1-containing substrate, which in turn activates the signaling required for lens fiber morphogenesis. In the images above, Fn1 is labeled in the developing lens of control zebrafish (top) and fn1 mutants (bottom). The control lens shows Fn1 (red) at the apical side of the lens epithelium (asterisks) and in lens fibers at the posterior (arrows), while the mutant shows reduced levels of Fn1.

Hayes, J., Hartsock, A., Clark, B., Napier, H., Link, B., & Gross, J. (2012). Integrin 5/fibronectin1 and focal adhesion kinase are required for lens fiber morphogenesis in zebrafish Molecular Biology of the Cell, 23 (24), 4725-4738 DOI: 10.1091/mbc.E12-09-0672

November 30, 2012

I didn’t pay enough attention to primary cilia in my earlier years, and that is one of life’s big regrets (well, regret is a strong word). They are very fascinating little sensory organelles, and the thought of primary cilia carrying the weight of neuron migration on their little basal body shoulders is impressive. Check out today’s image, from a paper showing the role of primary cilia in brain development.

Neurons are frequently born far from their final home in the brain, and this migration is key to healthy nervous system development and function. A recent paper shows the importance of primary cilia in the migration of interneurons (neurons that connect one neuron to another) in the cerebral cortex. Primary cilia are microtubule-based sensory organelles that project out of a cell’s membrane. Higginbotham and colleagues imaged migrating interneurons in the developing cerebral cortex and found a correlation between primary cilia dynamics and interneuron mobility. This process requires the ciliary protein Arl13b, a GTPase in the Arf/Arl family. Arl13b ensures correct localization and movement of guidance cue receptors in primary cilia. In the images above, interneurons (green chamber in cartoon, green cells in images) migrate along tracks toward a signal secreted by dorsal cortical cells (blue chamber in cartoon). The migration of Arl13b mutant interneurons (right panel) was drastically reduced when compared to control interneurons (left, same scale).

Higginbotham, H., Eom, T., Mariani, L., Bachleda, A., Hirt, J., Gukassyan, V., Cusack, C., Lai, C., Caspary, T., & Anton, E. (2012). Arl13b in Primary Cilia Regulates the Migration and Placement of Interneurons in the Developing Cerebral Cortex Developmental Cell, 23 (5), 925-938 DOI: 10.1016/j.devcel.2012.09.019
Copyright ©2012 Elsevier Ltd. All rights reserved.

August 23, 2012

Art imitates life, but sometimes it is life that imitates art. And when I say “art,” I’m talking about my dance moves (don’t think it’s “art”?….get your own blog!). So, imagine my happiness at seeing that neutrophils have their own interpretation of my lasso dance move to help them roll within a vessel. Today’s image is from a fascinating paper describing this neutrophil sling.

Neutrophils are white blood cells that are some of the first responders to inflammation. Their migration toward inflamed tissue is made difficult due to the high shear stress of blood flowing through the vessel. Past research showed that neutrophils roll over the vessel’s surface by flattening and using long membrane tethers at the rear of the cell. A recent paper shows that these rear tethers are, in fact, the remnants of a sling that the neutrophil uses to roll within the vessel. Sundd and colleagues show that as a neutrophil rolls forward, a sling wraps itself around the cell and lays in front of the cell. The sling is then used as an adhesive substrate on which the cell can roll easily within the microvessel environment. As the cell rolls forward, the sling is peeled up and the process is repeated. The images above show two different neutrophils using a sling for forward rolling. The back tether of the sling (arrowhead, top images) is swung to the front of the cell (long white arrows, second images down), after which the cell moves forward.

Prithu Sundd,, Edgar Gutierrez,, Ekaterina K. Koltsova, Yoshihiro Kuwano, Satoru Fukuda, Maria K. Pospieszalska, Alex Groisman, & Klaus Ley (2012). ‘Slings’ enable neutrophil rolling at high shear Nature, 488 (7411), 399-403 : doi:10.1038/nature11248

Adapted by permission from Macmillan Publishers Ltd, copyright ©2012

June 14, 2012

You have this friend who is good at everything. He bakes cookies for sick kids at the hospital, he’s grand champion of all trivia nights at your local bar, he takes violin lessons every week, he works out every morning before the sun rises, and it’s just so annnnnooying how perfect he is and how much you want to be like him. Well, take that formins! You’re everywhere, and it’s annoying how good you are at your jobs! Today’s image is from a paper showing a novel role for the Diaphanous-related formin FMNL2.

Formins are actin filament-polymerizing proteins that are important in numerous cellular processes including cell polarity, cytokinesis, and cell migration. Although Diaphanous-related formins can form linear bundles of actin filaments similar to those in filopodia, the membrane protrusions seen on crawling cells, they haven’t been directly shown to play a role in filopodia formation. Block and colleagues recently found that the Diaphanous-related formin called FMNL2 accumulates at filopodia tips and lamellipodial membrane protrusions. In addition, FMNL2 drives actin elongation within filopidial tips and lamellipodia, in turn driving efficient cell migration, with the help of the well-studied polarity protein Cdc42. Images above show two time-lapse series of FMNL2 in crawling cells. FMNL2 is found at the filopodial tip (white arrows, left-hand images) and at the edge of a lamellipodial protrusion (arrowheads, right-hand images).

Block, J., Breitsprecher, D., Kühn, S., Winterhoff, M., Kage, F., Geffers, R., Duwe, P., Rohn, J., Baum, B., Brakebusch, C., Geyer, M., Stradal, T., Faix, J., & Rottner, K. (2012). FMNL2 Drives Actin-Based Protrusion and Migration Downstream of Cdc42 Current Biology, 22 (11), 1005-1012 DOI: 10.1016/j.cub.2012.03.064

Copyright ©2012 Elsevier Ltd. All rights reserved.

 

May 17, 2012

Hit the road, Jack! Cells undergo cell death all the time, but it’s important for a tissue to clear these cells out before problems crop up. Today’s image is from a paper showing the migration of apoptotic cells, and revealing the role a protein called elmo1 in cell corpse clearing.

Apoptosis is programmed cell death, and is as part of normal development and tissue function as cell division is. Apoptotic cells must be cleared out of the healthy tissue, and failure to do so can result in inflammation and autoimmunity. A recent paper describes the clearance of apoptotic cells in the developing brain of zebrafish, using real-time microscopy to track apoptotic cells. van Ham and colleagues found that apoptotic cells are able to migrate to the periphery of the tissue to contribute to their own removal, and use their own actin cytoskeleton to do so. Later in development, cell corpses are engulfed by large macrophage cells with the help of a protein called elmo1, a protein known to play a role in cell engulfment in other tissues. In the images above, a cell in the process of undergoing apoptosis migrates through the neural tube of a zebrafish embryo.

van Ham, T., Kokel, D., & Peterson, R. (2012). Apoptotic Cells Are Cleared by Directional Migration and elmo1- Dependent Macrophage Engulfment Current Biology, 22 (9), 830-836 DOI: 10.1016/j.cub.2012.03.027
Copyright ©2012 Elsevier Ltd. All rights reserved.