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