May 27, 2010

During mitosis, chromosome segregation depends on proper assembly and function of kinetochores, which are protein complexes necessary for chromosome attachment to the microtubules of the spindle. Kinetochores are made of dozens of proteins, and the accurate assembly, localization, and dynamics of these proteins are important. A recent paper has shown that the chaperone complex Hsp90-Sgt1 interacts with Mis12, a known key player in kinetochore assembly. Image above shows mitotic spindles lacking proper Sgt1 function, with only very stable kinetochore-bound microtubules preserved. Some spindles with this treatment look normal (top), while many others have kinetochores without microtubule attachment (arrowheads). Kinetochores are in red, microtubules in green, and DNA in blue.

Reference: Alexander E. Davies and Kenneth B. Kaplan, 2010. Originally published in Journal of Cell Biology, doi: 10.1083/jcb.200910036. Paper can be found here.

May 24, 2010

Phagocytosis is the process in which solid material is endocytosed in the cell. Investigators recently worked through the details of the involvement of the actin cytoskeleton, myosin, and actin-binding proteins in efficient phagocytosis. Actin-binding proteins are enriched in concentric rings at the furrow site where the phagosome eventually closes off, and image above shows the actin motors MyoK (green) and myosin II (red) at the furrow of the amoeba Dictyostelium engulfing budding yeast cells.

Reference: Régis Dieckmann, Yosuke von Heyden, Claudia Kistler, Navin Gopaldass, Stéphanie Hausherr, Scott William Crawley, Eva C. Schwarz, Ralph P. Diensthuber, Graham P. Côté, Georgios Tsiavaliaris, and Thierry Soldati. Authors’ Molecular Biology of the Cell paper can be found here.

May 20, 2010

Chromosome architecture is tightly regulated during mitosis, from condensation and cohesion of chromosome arms early in mitosis, to chromosome cleavage and separation in anaphase. A recent paper uncovers a pathway that is critical for proper chromosome architecture; an ATPase called PICH works with the kinase Plk-1 to regulate chromosome arm cohesion and organization during mitosis. Image above shows chromosomes during mitosis, stained for Plk-1 (left, red in merged image), PICH (center, green in merge), and DNA (right, blue in merge).

Reference: Yasuhiro Kurasawa and Li-yuan Yu-Lee. Authors’ Molecular Biology of the Cell paper can be found here.

May 17, 2010

In endocytosis, material is taken into the cell and is transported around the cell in vesicles, or endosomes, with different functions and associated proteins. A recent paper has shown the transition of an early endosome into a late endosome, using live imaging of a scavenger cell called a ceolomocyte, in the worm C. elegans. Image above shows this transition, with early endosomes in green and late endosomes in red. The arrow is pointing to one particular endosome as it transitions into a late endosome.

Reference: Dmitry Poteryaev, Sunando Datta, Karin Ackema, Marino Zerial, and Anne Spang. Cell 141, 497-508. ©2010 Elsevier Ltd All rights reserved. Paper can be found here.

May 13, 2010

The tight junctions in between epithelial cells play an important role in preventing material from crossing the epithelial sheet. In some intestinal diseases, a cytokine called TNF (for tumor necrosis factor) contributes to the loss of this barrier by disruption of tight junctions. A recent paper shows that TNF induces endocytosis, or internalization, of certain tight junction proteins, which in turn results in barrier loss. Image shows the tight junction proteins occludin (green) and ZO-1 (red) in epithelial cells.

Reference: Image is from the cover of Journal of Cell Biology, April 5, 2010. Amanda M. Marchiando, Le Shen, W. Vallen Graham, Christopher R. Weber, Brad T. Schwarz, Jotham R. Austin II, David R. Raleigh, Yanfang Guan, Alastair J.M. Watson, Marshall H. Montrose, and Jerrold R. Turner, 2010. Originally published in Journal of Cell Bioloy. doi: 10.1083/jcb.200902153. Paper can be found here.

May 10, 2010

The actin and microtubule cytoskeletal networks frequently interact together during cellular processes. A recent paper has uncovered an important role for a protein called Short stop, a member of the spectraplakin family of proteins, that serves to crosslink actin and microtubules at the cell periphery. Through this interaction with the actin cytoskeleton, Short stop functions to regulate microtubule organization. Image above shows Short stop (red) along the lengths of microtubules (green) at the cell periphery.

Reference: Derek A. Applewhite, Kyle D. Grode, Darby Keller, Alireza Zadeh, Kevin C. Slep, and Stephen L. Rogers. Authors’ Molecular Biology of the Cell paper can be found here.