Happy Holidays!

HighMag will be taking a short break to celebrate the holidays! See you next year!

December 19, 2011

Just when you think the mitotic spindle can’t get any more magical, the Ran pathway comes out and says, “I’m here, beyotch!” Today’s image is from a paper showing how kinetochore fibers are stabilized using a Ran-dependent mechanism.

The mitotic spindle is a complicated apparatus that functions to separate chromosomes during mitosis through the attachment of microtubules to kinetochores on chromosomes. Many of these microtubules are sourced from a pair of centrosomes on either side of the spindle, but there is a population of important microtubules that are not generated at centrosomes. These “acentrosomal” microtubules are instead generated by the presence of RanGTP around the chromosomes. The idea is that these microtubules are able to capture kinetochores easily by being nucleated so close to them. The other ends (minus ends) of these acentrosomal microtubules are focused near the centrosomes, and a recent paper describes how these microtubules are stabilized. A protein called MCRS1 is a RanGTP-regulated protein and is found at the minus ends of chromosomal and kinetochore microtubules, according to Meunier and Vernos. MCRS1 stabilizes kinetochore fiber microtubules, and without it, spindles are unstable. As seen in the images above, MCRS1 (middle row, green in merged) is localized to the minus ends of microtubules (top row, red in merged). MCRS1 localization is more obvious (arrow in higher mag image) when only kinetochore fiber microtubules are present (middle column) when compared with control (left column). When kinetochore fibers are absent (right column), so is MCRS1.

ResearchBlogging.orgMeunier, S., & Vernos, I. (2011). K-fibre minus ends are stabilized by a RanGTP-dependent mechanism essential for functional spindle assembly Nature Cell Biology, 13 (12), 1406-1414 DOI: 10.1038/ncb2372
Adapted by permission from Macmillan Publishers Ltd, copyright ©2011

December 15, 2011

Instead of fat-shaming our fat cells, we need to thank them for providing our bodies with essential energy. Lipid droplets play an important role in storing this fat and are quite dynamic. Today’s image is from a paper describing the dynamics that allow lipid droplets to grow.

Lipid droplets (LDs) are dynamic lipid storage organelles that participate in a variety of cellular processes. Lipid droplet misregulation has been linked to diseases such as diabetes and obesity. A recent paper sheds light on how LDs grow, and describes how an LD-associated protein called Fsp27 contributes to LD growth. Gong and colleagues found that Fsp27 is enriched at the points where two lipid droplets contact each other. Lipids are exchanged between the two LDs at these contact points, with a net lipid transfer from smaller to larger LDs that eventually results in the merging of the LDs. Images above are of adipocytes, which are specialized cells that store fat for energy, showing Fsp27 (red in all images) localization on lipid droplets (green in top row). The points where two LDs contact each other has an enrichment of Fsp27 (arrowheads). Other LD-associated proteins (green in middle, bottom rows), however, are not enriched at LD contact sites.

ResearchBlogging.orgGong, J., Sun, Z., Wu, L., Xu, W., Schieber, N., Xu, D., Shui, G., Yang, H., Parton, R., & Li, P. (2011). Fsp27 promotes lipid droplet growth by lipid exchange and transfer at lipid droplet contact sites originally published in The Journal of Cell Biology, 195 (6), 953-963 DOI: 10.1083/jcb.201104142

December 12, 2011

If you have ever lived or worked with me (or are that poor guy who is married to me), then you know that I like things neat and organized. Anything less will send me into a sad tailspin that involves boxed wine and Cheetos. Thankfully, there are enough stunningly beautiful examples of precision, order, and patterning throughout biology to make me happy….like, really happy. Today’s image is from a paper that describes how the different cells in a fruit fly’s eye arrange into the honeycomb pattern seen above.

One of the big questions in developmental biology is how groups of different cell types arrange themselves to form a functional organ. A fantastic model to study this question is the compound fruit fly eye, made of hundreds of ommatidia. A group recently looked at how the several cell types in the developing fly eye are able to reorganize themselves into their honeycomb lattice. The very precise local movements of these cells, according to Johnson and colleagues, require regulation by a protein called Arf6 GTPase in order to connect cell surface signaling with the cytoskeletal rearrangements required for cell motility. The adaptor protein, Cindr, is able to bind to and sequester Arf6 activators called ArfGAPs, which in turn prevents local Arf6 activity. Images above show the precise honeycomb organization in a normal fruit fly pupal eye. In the developing eye (shown chronologically from left to right), the cone cells (orange in cartoon) of each ommatidia are surrounded by a hexagon lattice of cells.

ResearchBlogging.orgJohnson, R., Sedgwick, A., D'Souza-Schorey, C., & Cagan, R. (2011). Role for a Cindr-Arf6 axis in patterning emerging epithelia Molecular Biology of the Cell, 22 (23), 4513-4526 DOI: 10.1091/mbc.E11-04-0305

ASCB treat

The American Society of Cell Biology (ASCB) is a huge organization of about 10,000 cell biologists. This organization is fantastic for not only the support of biology research, but also for its help in career development, discussions of women in the sciences, support of biology education at every level, and influence on public policy.

The ASCB holds an annual meeting that is the top meeting choice for many cell biologists. This year's meeting wrapped up earlier this week, so I figured I would devote today's blog post to a favorite meeting event--Celldance! This isn't a dance for cell biologists (go the International C. elegans meeting for that rad event that lets you boogie with Nobel laureates...I'm looking at you, Craig Mello!). Celldance is a competition for stunning images and movies of cells. Movies can be descriptive or experimental, new or old, or they can help describe a cellular event for students and the general public.

So, please enjoy a few of the 2011 Celldance winners (and check out past winners here), courtesy of ASCB:

First place award: Cancer Dance - a stunning look at what may contribute to malignancy in some cells (Submitted by Tsutomu Tomita of Timelapse Vision, Inc.)

Public outreach award: Animation of Chromosome Alignment and the Spindle Assembly Checkpoint - beautiful, with sparkly animation of the amazing kinetochore and spindle checkpoint that makes me think of Katy Perry's "Firework" video (Submitted by Bin He, Virginia Tech)

Check out the rest of the 2011 CellDance winners here.

BONUS!! ASCB also announced winners of the first World Cell Race! This race pitted multiple cell types from labs all over the world against each other on race tracks made of fibronectin. The fastest cells were bone marrow stem cells, which clocked in at 5.2 microns per minute (or 0.000204 inches per minute). Check out the World Cell Race homepage for a movie of cells racing.

December 5, 2011

When I read papers like the one that gave us today’s image, I think that one day my wish of jumping into a cell to float in the cytoplasm wearing goggles and swimmies may actually come true. Physical manipulation of proteins gets me so excited about how far our tools and technology have come. In this paper, biologists physically yanked on actin filaments to show how tension affects the presence and function of an actin-modulating protein.

Actin has many regulatory proteins that do a variety of things, such as promoting filament nucleation, branching, and severing. Cofilin is a ubiquitous protein that functions in actin filament severing and reorganization. Cofilin binds to the actin filament itself and induces a slight twist in the actin, which makes it easily severed. A recent paper describes the use of optical tweezers and manipulations to show that the binding of cofilin to actin, and in turn its severing of actin, is regulated by tension in the filaments. Hayakawa and colleagues bound one end of an actin filament to a glass coverslip and manipulated the other end using optical tweezers. When the filament was put under tension, the actin filament was not severed (or it took longer, in some cases). In another manipulation, a fine glass pipette was used to pull bundles of actin. Tension applied to the actin filaments caused a drop in the binding rate of cofilin to actin filaments, as seen in the images above. Top row shows actin (left) and cofilin (right, fat arrows) in a tension-relieved actin bundle, while bottom row shows actin and reduced cofilin binding in an actin bundle that was stretched by 20%.

ResearchBlogging.orgHayakawa, K., Tatsumi, H., & Sokabe, M. (2011). Actin filaments function as a tension sensor by tension-dependent binding of cofilin to the filament originally published in The Journal of Cell Biology, 195 (5), 721-727 DOI: 10.1083/jcb.201102039

December 1, 2011

There are a lot of times when I wish I was a fly on the wall during a totally awesome experiment I’ve read about. This is not one of them, but purely for my own safety. Today, I share with you a humbling and stunning image of the deadly Marburg virus, a virus so pathogenic it requires intense special handling and facilities.

The filovirus family is made of the Ebola and Marburg viruses, which cause deadly hemorrhagic fevers in humans and non-human primates. All filoviruses are single-stranded RNA viruses, yet their range of morphologies is an obstacle in understanding the structure and assembly of these viruses. In addition, the intense containment conditions (called biosafety level 4) required to work with these viruses make many techniques either difficult or impossible. A group of biologists recently jumped over all of these hurdles to image Marburg virus particles using a variety of electron microscopy techniques. Bharat and colleagues are the first to show a detailed 3-D structure of a biosaftely level 4 pathogen, both after release and during virus assembly within an infected cell. In addition, Bharat and colleagues determined the location of different viral proteins within the virus. Above is a cryo-electron microscopy image of Marburg virus particles. All three different morphologies—filamentous, 6-shaped, and round—have spine-like protrusions coming from the virus particle membrane (arrowheads). Inset image shows striations just under the membrane in a filamentous virus particle.

ResearchBlogging.orgBharat, T., Riches, J., Kolesnikova, L., Welsch, S., Krähling, V., Davey, N., Parsy, M., Becker, S., & Briggs, J. (2011). Cryo-Electron Tomography of Marburg Virus Particles and Their Morphogenesis within Infected Cells PLoS Biology, 9 (11) DOI: 10.1371/journal.pbio.1001196