August 30, 2010

Septins make up a large family of proteins that have diverse roles, most notably in cell division. Some septins are found in neuronal tissue, and a recent paper demonstrates a role for one of the septins in neuronal migration. Images show neurons (white) in the developing mouse brain with or without normal levels of Septin 14. Without normal levels of Septin 14 (right), many neurons are not able to migrate to the correct layer of the tissue, compared to control neurons (left).

Reference: Tomoyasu Shinoda, Hidenori Ito, Kaori Sudo, Ikuko Iwamoto, Rika Morishita, and Koh-ichi Nagata. Authors’ Molecular Biology of the Cell paper can be found here.

August 26, 2010

Pathogens such as viruses and bacteria must move within infected cells in order to replicate and spread to other cells. Viruses typically hijack the cell’s microtubule cytoskeleton for motility within the cell, while bacteria typically use actin-based mechanisms. Authors of a recent paper have demonstrated how a baculovirus type species uses actin polymerization to first move to the cell’s nucleus, then later move to the cell surface in order to quickly spread to nearby cells. Image above shows an infected cell with the virus (red) translocated to spikes at the cell’s surface. Actin is in green.

Reference: Taro Ohkawa, Loy E. Volkman, and Matthew D. Welch, 2010. Originally published in Journal of Cell Bioloy. doi: 10.1083/jcb.201001162. Paper can be found here.

August 23, 2010

APC is a tumor suppressor commonly mutated in cancer, and normally functions in several different processes including signaling, cell migration, and cell-cell adhesion. A recent paper shows how different sub-cellular localizations of APC have different functions, and are independently regulated. APC can be found in punctuate clusters, associated with microtubules at membrane extensions, or on the lateral membranes, associated with actin and cell-cell contacts. Images show the association of many actin filaments (green) with the lateral localization of APC (red, “L” is top inset), compared to a smaller number of actin filaments found at APC clusters in membrane extensions (“C” inset is bottom).

Reference: Elizabeth S. Harris, and W. James Nelson. Authors’ Molecular Biology of the Cell paper can be found here.

August 19, 2010

Early steps in the development of the mouse embryo lead to establishment of the anterior-posterior axis (future head to tail axis). This process depends on a group of cells called the anterior visceral endoderm (AVE), which migrates from the bottom of the embryo to a position that overlies the eventual head. The AVE migrates as a collective group of cells, and a recent paper has found that the GTPase Rac1 is required for this migration event. Above is a set of time-lapse images of an AVE cell from a wild-type (top) or Rac1 mutant (bottom) embryo. The cells are painted in the bottom row of each set of images, highlighting the lack of long protrusions in the Rac1 mutant compared to the wild-type cell.

Reference: Isabelle Migeotte, Tatiana Omelchenko, Alan Hall, Kathryn V. Anderson. Authors’ PLoS Biology paper can be found here.

August 16, 2010

Neurons must be kept healthy in order to function properly, and when this maintenance is disrupted due to injury or disease, the neuron undergoes degeneration. A recent paper has identified a protein called Nmnat2 as a survival factor for neurons—without it, neurons begin to undergo degeneration. Nmnat2 proteins turn over rapidly within the axon of the neuron, and its levels decrease rapidly after injury to the neuron. Images above show projections from neurons with normal (left) or reduced (right) levels of Nmnat2; reduced levels of Nmnat2 result in multiple swellings, which precede degeneration of the neuron.

Reference: Jonathan Gilley and Michael P. Coleman. Authors’ PLoS Biology paper can be found here.

August 12, 2010

The centromere is a region on a chromosome where sister chromatids are joined together, and where the kinetochore is assembled in order to attach to the mitotic spindle. Centromeres do not have a specific DNA sequence, but do have several unique features including highly repetitive DNA sequences. A recent paper has found that these repetitive sequences are important to generate a fully functional centromere. The authors used a cell line where one chromosome has relocated its centromere, but left the repetitive sequence at the old centromere’s site. Image above shows the chromosomes from this cell line, with zoomed images of the chromosome with the new centromere. A protein called CENP-A (top) labels the new centromere (arrowhead), while a more general centromere label (bottom) is found on both the new and old (asterisk) centromere sites.

Reference: Emily A. Bassett, Stacey Wood, Kevan J. Salimian, Sandya Ajith, Daniel R. Foltz and Ben E. Black, 2010. Originally published in Journal of Cell Bioloy. doi: 10.1083/jcb.201001035. Paper can be found here.

Great blurb about this paper can be found here.

August 9, 2010

Microtubules are an important component of the cell’s cytoskeleton, and function in many roles including mitosis, cytokinesis, migration, and membrane trafficking. They are very dynamic structures, and the list of proteins that are associated with them is long. One such protein is called CLIP-170, which is found on the tips of microtubules as they grow and serves to regulate each microtubule’s dynamics and interaction with other structures in the cell. A recent paper has shown that the association of CLIP-170 to microtubule tips is altered after mutating certain regions of CLIP-170, which in turn alters the protein’s conformation, or three-dimensional shape. Image above shows mammalian cells with normal and mutated CLIP-170 on growing microtubules (whole cells are top, magnified views of single microtubule tips are bottom). The two mutated proteins have greater (middle) or decreased (right) association with microtubules compared to normal CLIP-170 (left).

Reference: Ho-Sup Lee, Yulia A. Komarova, Elena S. Nadezhdina, Rana Anjum, John G. Peloquin, Joseph M. Schober, Oana Danciu, Jeffrey van Haren, Niels Galjart, Steven P. Gygi, Anna Akhmanova, and Gary G. Borisy. Authors’ Molecular Biology of the Cell paper can be found here.

August 5, 2010

Motile cells move in response to environmental cues, and have complex networks that allow them to change their direction accordingly. The rod-shaped bacterium Myxococcus xanthus controls its motility by switching its own polarity from the front (leading) to the back (lagging) end depending on which direction it is headed, meaning that the mechanisms controlling movement are able to switch rapidly. A recent paper finds that the leading side of the cell accumulates a protein called MglA, while MglB is found at the lagging end of the cell where it inactivates MglA. Image above shows MglB (green) on the lagging end of a bacterium, even after it changes direction (middle of image).

Reference: Yong Zhang, Michel Franco, Adrien Ducret, Tâm Mignot. Authors’ PLoS Biology paper can be found here.

August 2, 2010

After material is taken into a cell, it is transported in vesicles to different destinations. These vesicles are very dynamic—they frequently fuse together to form larger vesicles, or undergo fission to form smaller vesicles. A recent paper shows that the fusion of late endosomes and lysosomes is regulated by ARL-8 GTPase. Image above shows labeled ARL-8 (red) and RME-8 (green) in a scavenger cell in the worm C. elegans. In the merged image (left), ARL-8 is not found on vesicles with RME-8, which labels early and late endosomes.

Reference: Isei Nakae, Tomoko Fujino, Tetsuo Kobayashi, Ayaka Sasaki, Yorifumi Kikko, Masamitsu Fukuyama, Keiko Gengyo-Ando, Shohei Mitani, Kenji Kontani, and Toshiaki Katada. Authors’ Molecular Biology of the Cell paper can be found here.