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

July 21, 2011

When I think of mitochondria, I’m faced with a minor bout of nausea when I remember struggling to memorize all of the steps to oxidative phosphorylation during college. Although my college memories of Napster and the Y2K problem are clearer than those of the citric acid cycle, I know how important mitochondria are. A recent paper describes how mitochondria are anchored throughout the cell.

Mitochondria are organelles that provide metabolic energy to the cell. Depending on the energy needs in different regions of the cell, mitochondria move around using actin- and microtubule-based motors and then anchor themselves in place. A recent paper describes how intermediate filaments bind mitochondria to regulate their distribution and anchor them within the cell. Intermediate filaments provide mechanical strength in many cell types by forming rope-like networks of filaments, and are frequently made of a protein called vimentin. Nekrasova and colleagues found that in cells lacking vimentin, mitochondria were highly mobile within the cell. Images above show the colocalization of mitochondria (purple) and vimentin intermediate filaments (green) in mammalian cells. Middle and right images are higher magnification frames of the boxed regions.

Nekrasova, O., Mendez, M., Chernoivanenko, I., Tyurin-Kuzmin, P., Kuczmarski, E., Gelfand, V., Goldman, R., & Minin, A. (2011). Vimentin intermediate filaments modulate the motility of mitochondria Molecular Biology of the Cell, 22 (13), 2282-2289 DOI: 10.1091/mbc.E10-09-0766

May 2, 2011

The cytoskeleton is made of actin, microtubules, and intermediate filaments. Sometimes, those poor intermediate filaments fall out of the spotlight by the stage hogs, actin and microtubules. This is unfortunate, because intermediate filaments are quite beautiful, as you’ll see in today’s images.

Vimentin is an intermediate filament protein found in migrating cells. Migrating cells have lamellipodia, which are dynamic membrane ruffles found at the front of a migrating cell, and a recent paper looks at the role of vimentin in migration. Helfand and colleagues found that the disassembly of vimentin intermediate filaments at the cell’s periphery is important for the formation of lamellipodia and for motility. As seen in the images above, motile cells (top) do not have vimentin intermediate filaments in lamellipodia, and instead have a decreasing presence of long filaments as they approach the lamellipodia (a,b) and non-filamentous vimentin at the cell’s edge (c). Cells lacking lamellipodia (bottom), however, have vimentin intermediate filaments that extend to the cell’s periphery.

Helfand, B., Mendez, M., Murthy, S., Shumaker, D., Grin, B., Mahammad, S., Aebi, U., Wedig, T., Wu, Y., Hahn, K., Inagaki, M., Herrmann, H., & Goldman, R. (2011). Vimentin Organization Modulates the Formation of Lamellipodia Molecular Biology of the Cell DOI: 10.1091/mbc.E10-08-0699