March 26, 2015

The actin cytoskeleton at the leading edge of a crawling cell has been a source of both scientific fascination and stunning images for biologists. Today’s image is from a paper that sheds light on how that complex structure is generated. 

The outermost region of a crawling cell’s cortex is called the lamellipodium, and it depends on a complex actin cytoskeleton for its structure and rapid dynamics. The generation of branched actin filaments at lamellipodia requires the activity of the actin-nucleating Arp2/3 protein complex. In a recent study, Henson and colleagues use the very flat and Arp2/3-rich lamellipodia of sea urchin coelomocytes to visualize the actin cytoskeleton. As seen in the images above, treatment of coelomocytes with a drug that inhibits the Arp2/3 complex resulted in drastic changes to the actin cytoskeleton. Specifically, the densely-packed branched filaments of lamellipodia (left, control) were replaced with actin filament arcs that ran diagonal or parallel to the cell’s edge (30 and 60 seconds after drug treatment, middle and right images). These transverse actin arcs may act as mother/scaffold filaments from which more actin filaments are nucleated during organization of the cytoskeleton in lamellipodia.

Henson, J., Yeterian, M., Weeks, R., Medrano, A., Brown, B., Geist, H., Pais, M., Oldenbourg, R., & Shuster, C. (2015). Arp2/3 complex inhibition radically alters lamellipodial actin architecture, suspended cell shape, and the cell spreading process Molecular Biology of the Cell, 26 (5), 887-900 DOI: 10.1091/mbc.E14-07-1244

February 20, 2015

Even the simplest and most elegant song or painting still has a complicated story behind it. That’s what I’m thinking about as I read about cilia today. Cilia are simple and beautiful, but the axonemal structure of cilia is far more complex than one might first appreciate. Today’s image is from a paper describing a protein required for one of the ciliary radial spokes. 

Motile cilia are structures on the surface of some microscopic organisms and certain types of cells, and function in locomotion or the movement of fluid over the cell. Inside each of these cilia is a microtubule-based axoneme structure—9 outer doublets of microtubules form a circle around a central microtubule pair, with radial spokes connecting the center pair with the outer microtubules. These radial spokes are important for regulating ciliary motility. The cilia of most species have three radial spokes, but these spokes are not identical to one another, suggesting that each spoke has a unique functional role. In a recent collaboration between the Nicastro and Gaertig labs, Vasudevan and colleagues found that the ciliary protein FAP206 likely serves as a microtubule docking protein for one of the radial spoke proteins (RS2) and dynein c. In the top images above, FAP206-GFP can be seen exclusively in the cilia of interphase (left) and dividing (right) Tetrahymena cells. In the absence of FAP26, the axoneme lacked proper assembly of the radial spoke RS2. Cryo-electron tomography images (bottom) show a wild-type axoneme (left), with RS2 connecting to the A-tubule of an outer microtubule doublet, compared to an axoneme lacking FAP206, which lacks RS2 (right, arrowhead).

Vasudevan, K., Song, K., Alford, L., Sale, W., Dymek, E., Smith, E., Hennessey, T., Joachimiak, E., Urbanska, P., Wloga, D., Dentler, W., Nicastro, D., & Gaertig, J. (2014). FAP206 is a microtubule-docking adapter for ciliary radial spoke 2 and dynein c Molecular Biology of the Cell, 26 (4), 696-710 DOI: 10.1091/mbc.E14-11-1506

February 12, 2015

Biologists have to wear many hats, and one under-appreciated hat is that of marketing executive. You have to properly name whatever process/protein/structure you just identified so it will be easily remembered. Whoever coined the term “invadopodia” was spot-on….the term is informative, catchy, and ignites my imagination of what it’s like inside a cell. Today’s image is from a fascinating paper on invadopodia formation.

Invadopodia are dynamic protrusions of plasma membrane that locally degrade a cell’s underlying extracellular matrix (ECM). A tumor cell’s invadopodia mediate the invasion of tissue and metastasis. A recent paper describes a study of invadopodia formation within the context of a highly-concentrated collagen matrix, to better mimic the ECM of cancerous tissue. This dense collagen network, Artym and colleagues found, triggers robust invadopodia formation and ECM degradation, in both cancerous and non-cancerous cell lines. This invadopodia formation did not require altered gene or protein expression, but did require phosphorylation of kindlin2, part of a complex integrin regulatory network. As seen in the images, the high-density fibrillary collagen (HDFC, top) network triggered the induction of many more invadopodia (yellow dots) than a gelatin-based matrix (bottom).  

Artym, V., Swatkoski, S., Matsumoto, K., Campbell, C., Petrie, R., Dimitriadis, E., Li, X., Mueller, S., Bugge, T., Gucek, M., & Yamada, K. (2015). Dense fibrillar collagen is a potent inducer of invadopodia via a specific signaling network originally published in the Journal of Cell Biology, 208 (3), 331-350 DOI: 10.1083/jcb.201405099

January 8, 2015

If you are lucky in life, there is at least one person who will always be there for you—a parent, your spouse, maybe even your pooch. As we understand more and more of what goes on inside a cell, it has become clear that actin is always there for the cell’s many organelles. Actin is so supportive and encouraging, and without it our cells would just be puddles of fats and proteins. Today’s images are from a paper describing the role of actin in mitochondrial fission. 

Mitochondria are dynamic organelles that divide by fission. Although a role for the actin cytoskeleton in mitochondrial fission has been suggested, the exact mechanism is unclear. Recent work by Li and colleagues shows a transient association of F-actin (filamentous actin) to mitochondria at the start of fission. Downregulation of the actin regulators cortactin, cofilin, and Arp2/3 caused elongation of mitochondria. Li and colleagues tested the role of Drp1, which is a key player in mitochondrial division, on F-actin assembly during fission. Drp1 inhibition prolonged the localization of F-actin and several actin regulators at mitochondria during fission. In the left group of images above, F-actin (green) and mitochondria (red) are visible in a control mammalian cell (bottom row is at higher magnification). The group of images on the right shows mammalian cells after chemical induction of mitochondrial fission: 2 minutes after drug treatment, many F-actin-rich mitochondria are visible.

Li, S., Xu, S., Roelofs, B., Boyman, L., Lederer, W., Sesaki, H., & Karbowski, M. (2014). Transient assembly of F-actin on the outer mitochondrial membrane contributes to mitochondrial fission The Journal of Cell Biology, 208 (1), 109-123 DOI: 10.1083/jcb.201404050

December 18, 2014

You might not want the dreaded tube socks in your Christmas stocking this year, but you do appreciate the actual tubes that your body depends on in just about every organ system. A recent paper in PLOS Biology describes tube formation in the fly renal system and the signals that regulate it.

Tubes generally start as buds that dramatically elongate during development, but the cell rearrangements that occur during tubulogenesis are not completely understood. Saxena and colleagues recently used the developing fly renal system to track cell movements during tube formation. Tubule elongation primarily occurs through convergent extension, during which cells intercalate along the length of the tube. During these rearrangements, the number of cells around the circumference of the tube drops as the number of cells along the tube increases. Saxena and colleagues show that epidermal growth factor localized at the tip cells of the distal end of the tube guides the polarity of cell rearrangements, via polarization of Myosin II within individual cells. Finally, without proper tube elongation, animals have abnormal excretory function and osmoregulation, leading to lethality. In the images above, the top row shows failure of tube elongation after laser ablation of the distal tip cells (arrowheads). Bottom row shows normal tube elongation without laser ablation of tip cells (arrowheads).

Saxena, A., Denholm, B., Bunt, S., Bischoff, M., VijayRaghavan, K., & Skaer, H. (2014). Epidermal Growth Factor Signalling Controls Myosin II Planar Polarity to Orchestrate Convergent Extension Movements during Drosophila Tubulogenesis PLoS Biology, 12 (12) DOI: 10.1371/journal.pbio.1002013

November 26, 2014

 

Patterns are soothing for left-brained folks like me, with the exception being those terrible patterned holiday sweaters that will come out of mothball-ridden closets soon (unsettling for everyone, really). Today’s images are from a paper describing a new micropatterning technique to look at plasma membrane proteins. 

The plasma membrane of a cell is riddled with many multi-protein complexes that facilitate communication and transport. These complexes provide a challenge to biologists due to their ubiquitous localization around the cell, their large, complex size, and their transient interactions with proteins. A recent paper describes a technique to study signaling complexes at the plasma membrane, using micropatterns within the plasma membrane. Löchte and colleagues expressed a protein bait in a micropattern in a living cell’s plasma membrane. Dynamics of the interactions between the protein bait and ligand target can then be quantified using live microscopy and on a single-molecule level. Löchte and colleagues used the IFN interferon signaling complex, using one of the receptor units (IFNAR2) as bait. In the top images above, the micropatterned receptor bait (IFNAR2) was able to recruit the other IFN receptor subunit (IFNAR1, green) after the addition of the ligand (red; time represents the addition of the ligand). Bottom image shows a closer view of the high-affinity, micropatterned binding that requires simultaneous interaction of the ligand (red) with both receptor subunits.


Lochte, S., Waichman, S., Beutel, O., You, C., & Piehler, J. (2014). Live cell micropatterning reveals the dynamics of signaling complexes at the plasma membrane originally published in the Journal of Cell Biology, 207 (3), 407-418 DOI: 10.1083/jcb.201406032

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

November 12, 2014

You might think that the “kiss-and-hop” is a dance move strictly forbidden at a Duggar homeschool prom, but it refers to the quick dynamics of the microtubule-associated protein tau. Today’s image is from a paper describing unexpected results about how tau resides on and regulate microtubules without physically impeding microtubule motors. 

The microtubule-associate protein tau binds to and stabilizes the microtubules within an axon. As most tau is believed to decorate axonal microtubules, it was previously unclear how tau can function in its non-microtubule-dependent roles, or how the presence of tau does not interfere with microtubule motors and axonal transport. A recent paper by Janning and colleagues describes the use of single-molecule tracking of tau in living cells. Janning and colleagues found that tau resides on a single microtubule for 40ms before hopping to the next microtubule, and that this unexpectedly short residence time is sufficient to affect microtubule stability. This “kiss-and-hop” mechanism allows for normal axonal transport, and suggests how some tau functions away from microtubules. In the images above, tau (red) is labeled in mouse cortical neurons, as are microtubules (green) and the nucleus (blue).  

Janning, D., Igaev, M., Sundermann, F., Bruhmann, J., Beutel, O., Heinisch, J., Bakota, L., Piehler, J., Junge, W., & Brandt, R. (2014). Single-molecule tracking of tau reveals fast kiss-and-hop interaction with microtubules in living neurons Molecular Biology of the Cell, 25 (22), 3541-3551 DOI: 10.1091/mbc.E14-06-1099

October 28, 2014

If you’ve ever tried to get your kids to share a donut, you understand the importance to dividing things equally (and learning crucial lessons…just buy more donuts next time...I mean, seriously!). Cell division is no different—chromosomes and organelles must all get divided equally. Today’s images are from a paper showing how mitochondria are positioned during cell division in order to allow equal segregation.

Many years of research have focused on the equal segregation of chromosomes during cell division. Organelles such as mitochondria must also be segregated equally in a dividing cell, and errors in this process can lead to disease. A recent paper identifies the actin motor Myosin-XIX (Myo19) as a key player in mitochondrial partitioning during cell division. Myo19 is localized to mitochondria, and cells depleted of Myo19 have an abnormal distribution of mitochondria. Rohn and colleagues found that cells lacking Myo19 experience stochastic division failure, suggesting that mitochondria are physically preventing successful cell division. The images above show dividing cells labeled to visualize mitochondria (green) and the mitotic spindle (red) in control cells (top two rows) and cells depleted of Myo19 (bottom two rows). Without Myo19, mitochondria moved towards spindle poles at the onset of anaphase, causing an asymmetric distribution at division when compared with control cells.

BONUS!! Here is a rotating 3D reconstruction of an A549 stained to visualize microtubules (green), mitochondria (red), and DNA (blue). Omar Quintero, HighMag friend and a co-author from today’s paper, loves this image: “I like it because it reminds me of the scenes in StarWars where the Rebels are planning their attack on the Death Star.”

Rohn, J., Patel, J., Neumann, B., Bulkescher, J., Mchedlishvili, N., McMullan, R., Quintero, O., Ellenberg, J., & Baum, B. (2014). Myo19 Ensures Symmetric Partitioning of Mitochondria and Coupling of Mitochondrial Segregation to Cell Division Current Biology DOI: 10.1016/j.cub.2014.09.045

Copyright ©2014 Elsevier Ltd. All rights reserved.

October 24, 2014

There is a party going on at the ends of microtubules, but I wasn’t invited. That won’t stop me, or countless cell biologists out there, from peeping in the window to check out all of the microtubule shenanigans. Today’s image is from a paper describing how Doublecortin binds to microtubule ends.

The plus end of a microtubule is the primary site for growth and shrinkage, and interaction with several microtubule-associate proteins. Different microtubule end-binding proteins may interact with microtubules using different mechanisms: the end-binding protein EB1 relies on the nucleotide state of the tubulin at the microtubule end, while a recent paper shows how another protein, Doublecortin (DCX), relies on the curvature of microtubule ends for binding. DCX is a neuronal microtubule-associate protein that plays an important role throughout development, yet how it interacted with microtubule ends was previously unclear. Bechstedt and colleagues used single-molecule microscopy to show that DCX (images above, green in merged) binds with higher affinity to curved microtubules (magenta) than to straight microtubules. DCX mutations, which are found in patients with double cortex syndrome, prevent the protein from binding to curved regions of microtubules.

Bechstedt, S., Lu, K., & Brouhard, G. (2014). Doublecortin Recognizes the Longitudinal Curvature of the Microtubule End and Lattice Current Biology, 24 (20), 2366-2375 DOI: 10.1016/j.cub.2014.08.039
Copyright ©2014 Elsevier Ltd. All rights reserved.

October 17, 2014

For years, the prettiest cells to image were flat cells in a dish. Thanks to the tireless work of many, beautiful high-resolution images can now come from tissue within a living organism. Today’s image is from a paper showing improved techniques for imaging fine cellular processes within large volumes, from the lab of recent Nobel prize winner, Eric Betzig. 

A material’s refractive index refers to how light travels through it; the simplest example being how light bends when passed through water. The refractive index heterogeneities stemming from the many cell types, morphologies, and subdomains within a living organism are a challenge to microscopists. As described in a paper from earlier this year, Wang and colleagues improved on previous techniques for imaging within large volumes. Wang and colleagues use adaptive optics (AO), which corrects for the microscope’s aberrations that limit image resolution, in a mode fast enough to correct for the various aberrations within a large sample, without inducing photodamage or photobleaching. The image above shows a 3D rendering from deep within a living zebrafish brain, with oligodendrocytes (magenta) and neuronal nuclei (green) visible.

Wang, K., Milkie, D., Saxena, A., Engerer, P., Misgeld, T., Bronner, M., Mumm, J., & Betzig, E. (2014). Rapid adaptive optical recovery of optimal resolution over large volumes Nature Methods, 11 (6), 625-628 DOI: 10.1038/nmeth.2925
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

Nobel, Nobel, Nobel!!!!

Last week the Chemistry Nobel Prize went to three amazing biologists who have been steadily and remarkably improving the world of imaging.  Eric Betzig, Stefan Hell, and W.E. Moerner made Abbe's diffraction limit a mere hurdle to leap over, not a finish line.  We'll feature some work from Eric Betzig's lab later in the week, but until then check out the links below:

Great popular science descriptions of Betzig, Hell, and Moerner's accomplisments:
Beaming with Pride - From Slate, by Boer Deng
How the optical microscope became a nanoscope - Popular Science Background from the Royal Swedish Academy of Sciences

We've featured work from Eric Betzig before:  here and here.
We've also featured stunning images using STORM: here.

October 9, 2014

As Tom and Jerry have proven time and time again, repulsive forces are serious business and highly entertaining. Today’s image is from a paper describing how different cell types repel one another to help create boundaries between tissues. 

The study of how cells adhere to or repel one another is an important field of study in developmental biology. Ephrin ligands and their respective Eph receptors trigger repulsive cues between cells of different types. Many different tissue types express the same ephrins and Eph receptors, yet only those cells at the tissue interface repel one another. A recent study tests how these signals are integrated to provide repulsion at only the tissue interface, and not between cells of the same tissue. Rohani and colleagues used the dorsal ectoderm-mesoderm boundary of early frog embryos to find Eph-ephrin pairs that are expressed in complementary tissues. The cells at the boundary of the tissues have a combined Eph-ephrin repulsive signal that is sufficient for a repulsive force, suggesting a simple model of repulsion based on relative concentrations and binding affinities of Eph receptors and ephrins at tissue boundaries. The image above shows the higher concentration of EphB receptors (green) at the ectoderm-mesoderm boundary.

Rohani, N., Parmeggiani, A., Winklbauer, R., & Fagotto, F. (2014). Variable Combinations of Specific Ephrin Ligand/Eph Receptor Pairs Control Embryonic Tissue Separation PLoS Biology, 12 (9) DOI: 10.1371/journal.pbio.1001955

September 25, 2014

While taking an awesome cell biology course in college, I was coming to terms with my mother’s recent ovarian cancer diagnosis. The scientist in my head couldn’t shake the curiosity about how my mother’s cells could have betrayed her so royally. This intersection of basic cell biology and cancer kick-started my interest in cell biology research. Today’s image is from a paper showing a role for the ARF tumor suppressor in maintaining chromosomal stability. THIS paper is one of the million billion reasons why basic research is necessary and important. 

The ARF tumor suppressor is mutated or absent in many cancers, and is known to stabilize p53 in response to cellular stress. Other, p53-independent roles for ARF contribute to its role as a tumor suppressor, but are not well understood. A recent paper describes ARF’s function in chromosome segregation during mitosis, via Aurora B regulation. Britigan and colleagues show that loss of ARF results in aneuploidy, or an incorrect number of chromosomes, stemming from chromosome segregation and spindle organization defects. These defects can be rescued through overexpression of the Aurora B kinase, which helps ensure proper kinetochore-spindle interactions and is overexpressed in some cancers. In the images above, ARF-/- cells (right column) show defects throughout mitosis, when compared to normal cells (left). Defects include misaligned chromosomes during metaphase (top, middle rows), and lagging chromosomes during anaphase (bottom).

Britigan, E., Wan, J., Zasadil, L., Ryan, S., & Weaver, B. (2014). The ARF tumor suppressor prevents chromosomal instability and ensures mitotic checkpoint fidelity through regulation of Aurora B Molecular Biology of the Cell, 25 (18), 2761-2773 DOI: 10.1091/mbc.E14-05-0966

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

September 11, 2014

As your therapist likely tells you, understanding where you came from is key to accepting where you are now. Take that therapist’s task and multiply it by several million—you now understand the tough job ahead of developmental biologists trying to track cell lineages in complex organisms. Today’s colorful image is from a paper describing a new computational framework for reconstructing cell lineages. 

The successful tracking of cell position, division, and movement in a developing organism has been a goal for countless developmental biologists. Reconstructing cell lineages in organisms like fruit flies and mice, however, is difficult due to the complexity of cell organization and behavior, poor image quality of thick embryos, the enormous size of the data sets, and an uncompromising need for accuracy. A recent paper by Amat and colleagues describes the development and use of a new open-source framework that reconstructs cell lineages with high accuracy and speed. Their system uses four dimensional and terabyte-sized image data sets of nuclei-tracked embryos, imaged using three different types of fluorescence microscopy. The images above show the first reconstruction of early fruit fly nervous system development (S1 neuroblasts), with precursor cell tracks color-coded for time (purple to yellow).

Amat, F., Lemon, W., Mossing, D., McDole, K., Wan, Y., Branson, K., Myers, E., & Keller, P. (2014). Fast, accurate reconstruction of cell lineages from large-scale fluorescence microscopy data Nature Methods, 11 (9), 951-958 DOI: 10.1038/nmeth.3036
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

September 5, 2014

It is so nice to have a friend who truly complements you…someone similar to you, but different enough to pick up the slack of your own shortcomings. Today’s image is from a paper about the Laverne and Shirley partnership of Ena/VASP and mDia2. 

Crawling cells extend finger-like filopodia to probe the environment for cues and to establish adhesion of the cell to the substrate. Filopodia are composed of parallel bundles of actin that are quickly dynamic. Countless actin regulators affect filopodia formation, some of which have seemingly similar functions. The Enabled (Ena)/VASP and Diaphanous 2 (mDia2) proteins are both actin polymerases, but as a recent paper by Barzik and colleagues describes, they support filopodia formation in distinct, non-redundant ways. By using mouse embryonic fibroblasts lacking both Ena/VASP and mDia2, Barzik and colleagues found that filopodia formed using either Ena/VASP or mDia2 alone differed in number, actin filament organization, lifetime, and other parameters. Filopodia generated using mDia2 alone were not able to initiate integrin-dependent adhesion and lamellipodial protrusions. The image above shows a cell with both mDia2 (red) and Ena/VASP (green), with the two proteins colocalizing on a subset of filopodia (arrows).

Barzik, M., McClain, L., Gupton, S., & Gertler, F. (2014). Ena/VASP regulates mDia2-initiated filopodial length, dynamics, and function Molecular Biology of the Cell, 25 (17), 2604-2619 DOI: 10.1091/mbc.E14-02-0712

August 29, 2014

Stem cells in adults are responsible for tissue renewal and many cancers. So, the hunt for stem cells is important and has already been successful, with stem cell populations identified in countless types of tissues. Stem cells in the ovary, however, were shy to show themselves until a recent study using a marker for the Wnt protein Lgr5.

In adults, stem cells are responsible for maintaining homeostasis during normal wear and tear of a tissue. The ovary and its ovary surface epithelium (OSE) experience remodeling during adulthood, yet stem cells of the ovary have been hard to find. A recent paper by Ng and colleagues describes the identification of stem cells in the ovary using markers for the Wnt target protein Lgr5. Lgr5 marks stem cells in several epithelial tissues. Ng and colleagues identified Lgr5+ cells in the mouse ovary starting from ovary organogenesis and lasting into adulthood. Using lineage tracing, Ng and colleagues confirmed that Lgr5+ cells are, in fact, stem cells that contribute to development, homeostasis, and repair of the OSE and associated structures. In the images above, Lgr5+ cells (green) are visible in embryonic (left) and postnatal (middle, right) ovarian tissue.

Ng, A., Tan, S., Singh, G., Rizk, P., Swathi, Y., Tan, T., Huang, R., Leushacke, M., & Barker, N. (2014). Lgr5 marks stem/progenitor cells in ovary and tubal epithelia Nature Cell Biology, 16 (8), 745-757 DOI: 10.1038/ncb3000
Adapted by permission from Macmillan Publishers Ltd, copyright ©2014

August 26, 2014

If you have little ones in your house, you might assume that the phrase “randomly fluctuating forces” is referring to your home. This phrase actually refers to the background force in a cell coming from active and motor-driven cell processes. Today’s image is from a study that developed a way to measure these forces. 

Actin- and microtubule-based motors move many types of material around a cell to drive critical cellular events. These motor-driven movements and other active processes in the cell contribute to a background of fluctuating forces in a cell. These stochastic forces collectively drive random motion of organelles and proteins within a cell, in turn affecting the dynamics and metabolic state of a cell. To measure these forces, Guo and colleagues developed force spectrum microscopy (FSM) to directly quantify the fluctuating forces in a cell’s cytoplasm, specifically by measuring the movements of individual injected particles. Guo and colleagues found that these forces are strong enough to move both large and small components, and that malignant cells have a higher level of fluctuating forces compared to benign cells. Image above shows a cell with injected particles (green), with the 2-minute trajectories (black) superimposed.

Guo, M., Ehrlicher, A., Jensen, M., Renz, M., Moore, J., Goldman, R., Lippincott-Schwartz, J., Mackintosh, F., & Weitz, D. (2014). Probing the Stochastic, Motor-Driven Properties of the Cytoplasm Using Force Spectrum Microscopy Cell, 158 (4), 822-832 DOI: 10.1016/j.cell.2014.06.051
Copyright ©2014 Elsevier Ltd. All rights reserved.

August 21, 2014

Microtubules are known for their fascinating dynamics, but some cellular processes require a more stable microtubule cytoskeleton. Thankfully, these stable, acetylated microtubules are just as photogenic as their non-modified microtubule pals. Today’s image is from a paper describing the role of the protein paxillin in microtubule acetylation. 

Crawling cells require coordination of adhesive forces, cytoskeletal rearrangements, and cell polarization. Cell polarization helps to direct newly synthesized proteins to the leading edge of the crawling cell, relying on both a stable microtubule cytoskeleton and positioning of the Golgi apparatus in front of the nucleus. The stability of these long-lived microtubules is due to acetylation—a post-translational modification of α-tubulin. A recent study by Deakin and Turner uncovered a role for the focal adhesion scaffolding protein paxillin in regulating microtubule acetylation, which in turn regulates Golgi integrity and cell polarization. Paxillin modulates microtubule stability through its inhibition of HDAC6, an α-tubulin deacetylase, and does so in both normal and transformed cells. In the images above, depletion of paxillin (bottom) in malignant (left column) and normal (right column) cell types resulted in a drop of microtubule acetylation (yellow), compared to control cells (top).

Deakin, N., & Turner, C. (2014). Paxillin inhibits HDAC6 to regulate microtubule acetylation, Golgi structure, and polarized migration originally published in the Journal of Cell Biology, 206 (3), 395-413 DOI: 10.1083/jcb.201403039