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