July 29, 2010

The cytoskeleton of epithelial cells plays an important role in organization of the entire tissue. There are zonula adherens junctions that connect belts of actin within adjoining cells, and are important for epithelial sheet morphology and formation. This adhesion requires complex coordination of the actin cytoskeleton and its associated proteins. A recent paper has found that two isoforms of the same protein, myosin II, serve very different, but important, functions at these junctions. Image above shows epithelial cells with myosin IIA (green) and myosin IIB (magenta), and the merged image showing colocalization. The computer model image shows a 3D reconstruction of localization and intensity data, with color maps representing the intensity ranges of myosin IIA (min=blue, max=green) and myosin IIB (min=red, max=yellow).

Michael Smutny, Hayley L. Cox, Joanne M. Leerberg, Eva M. Kovacs, Mary Anne Conti, Charles Ferguson, Nicholas A. Hamilton, Robert G. Parton, Robert S. Adelstein and Alpha S. Yap. Reprinted by permission from Macmillan Publishers Ltd: Nature Cell Biology 12, 696 – 702, copyright 2010. Paper can be found here.

July 26, 2010

Meiosis is a special type of cell division that results in the formation of gametes (sperm and eggs). Meiosis is made of two rounds of division that ultimately results in half the chromosomes, so that there is an accurate number of chromosomes after fertilization of the gametes. A recent paper describes an important role for a kinase called Aurora-C in ensuring accurate chromosome segregation in meiosis. Image above shows metaphase of the first meiotic division in control (left) and Aurora-C-deficient (right) mouse oocytes. Microtubules are in green, DNA is in blue, and kinetochores are in red in both whole oocyte (top) and zoomed in images of the spindles (bottom). In the Aurora-C-deficient oocyte, there is aberrant chromosome alignment and attachment to the spindle.

Reference: Kuo-Tai Yang, Shu-Kuei Li, Chih-Chieh Chang, Chieh-Ju C. Tang, Yi-Nan Lin, Sheng-Chung Lee, and Tang K. Tang. Authors’ Molecular Biology of the Cell paper can be found here.

July 22, 2010

Cell migration is a complex process that requires major remodeling of the cytoskeleton. A recent paper has demonstrated an important role for an isoform of calponin, an actin-binding protein, in cell motility. This calponin isoform controls cell migration via its association with and regulation of a major signaling cascade. Image above shows the calponin isoform(red) colocalizing with actin(green) in fibroblast cells (DNA is in blue, merged image is on right).

Reference: Sarah Appel, Philip G. Allen, Susanne Vetterkind, Jian-Ping Jin, and Kathleen G. Morgan. Authors’ Molecular Biology of the Cell paper can be found here.

July 19, 2010

The development of individual organs involves precise patterning of cells. The regulation of cell growth and division plays a large role in generating this patterning, and a recent paper used the sepal of the plant Arabidopsis thaliana as a model to investigate this. The sepal is the outer green, leaf-like floral organ on the plant, and is made of a distinct pattern of cells with a wide range of sizes. Image above is a scanning electron micrograph of an Arabidopsis sepal with giant cells colored red.

Reference: Adrienne H. K. Roeder, Vijay Chickarmane, Alexandre Cunha, Boguslaw Obara, B. S. Manjunath, Elliot M. Meyerowitz. Authors’ PLoS Biology paper can be found here.

July 15, 2010

The different sub-populations of microtubules of the mitotic spindle play different roles. Astral microtubules interact with the cell cortex, and this contact is important for regulating the position of the cleavage furrow that begins cytokinesis, the splitting of the cell into two daughter cells. A recent paper shows that after treatment to elongate astral microtubules, the mitotic spindle rocked severely. This rocking is due to a change in the location of the actin cytoskeleton at the cortex prior to cytokinesis. Image above shows mitotic cells with (right) or without (left) the treatment to elongate astral microtubules, and higher magnified regions underneath.

Reference: Kathleen E. Rankin and Linda Wordeman, 2010. Originally published in Journal of Cell Bioloy. doi: 10.1083/jcb.201004017. Paper can be found here. Check out the authors’ cover image for the same issue of JCB here.

July 12, 2010

Cilia are microtubule-based cellular protrusions, and there are two types – motile and non-motile. Non-motile, or “primary,” cilia function in sensory reception and signaling. This signaling role of primary cilia means that signaling receptors must be sorted to their elongated plasma membrane. A recent paper shows the ability of a complex of proteins called the BBSome to assemble a coat complex that can transport and sort membrane proteins to cilia. Image above is of artificial vesicles called liposomes mixed with members of the BBSome, and the arrowheads are pointing to surfaces coated with the BBSome complex.

Reference: Hua Jin, Susan Roehl White, Toshinobu Shida, Stefan Schulz, Mike Aguiar, Steven P. Gygi, J. Fernando Bazan and Maxence V. Nachury. Cell 141, 1208-1219. ©2010 Elsevier Ltd. All rights reserved. Paper can be found here.

July 8, 2010

A neuron’s dendrites are responsible for relaying signals from a stimulus or other neuron, and their branched patterns are important for the specific function of each type of neuron. In the worm C. elegans, the PVD neurons are mechanoreceptors that trigger an avoidance response after a touch stimulus. The dendrites of PVDs are repetitive structures that look like candelabras or menorahs. Image above shows a worm with a fluorescent signal in PVD neurons. A recent paper describes the role of a cell fusion protein called EFF-1 in regulating the formation of these menorahs, showing that EFF-1 sculpts the branching of the menorahs.

Reference: Meital Oren-Suissa, David H. Hall, Millet Treinin, Gidi Shemer, and Benjamin Podbilewicz. Similar images can be found in their Science paper, which can be found here.

July 5, 2010

During development of different tissues, there are pools of progenitor cells from which different cell types are formed. The mechanisms regulating how cell fate is determined are not completely understood, but a paper earlier this year helps to clarify this process in the developing retina. The authors identify a role for Blimp1, a transcription factor, in regulating the cell fate decision of the progenitor cells. Image shows retinal tissue from mice with (left) and without (right) Blimp1, after the cells have undergone differentiation into the different cell types. Without Blimp1, retinas had a thinner outer layer (bracket) and a thicker inner layer, as well as incorrect numbers of certain cells (red cells).

Reference: Joseph A. Brzezinski IV, Deepak A. Lamba and Thomas A. Reh, 2010. Development: 137, 619-629. doi: 10.1242/dev.043968. Adapted with permission by Development. Paper can be found here.

July 1, 2010

Some of the material that is internalized into the cell through endocytosis is destined for degradation in lysosomes. During transport to lysosomes, material is organized in multivesicular bodies, which are endosomal vesicles that have budded inward to acquire cargo-containing vesicles of their own. Proteins called ESCRTs are important for the formation of these multivesicular bodies, and a paper earlier this year shows how the ESCRT complexes contribute to multivesicular body biogenesis. Image above shows giant unilamellar vesicles created in the lab (entire vesicle is top, zoomed image of a different vesicle is bottom). Membrane (red), ESCRT-I protein (green), and cargo (blue) are all labeled (images on right are merged images). The membrane is budding into the vesicle, and the ESCRT can be seen at the neck of the bud.

Reference: Thomas Wollert and James H. Hurley. Adapted by permission from Macmillan Publishers Ltd: Nature 464, 864-869, copyright 2010. Paper can be found here.