August 26, 2014

If you have little ones in your house, you might assume that the phrase “randomly fluctuating forces” is referring to your home. This phrase actually refers to the background force in a cell coming from active and motor-driven cell processes. Today’s image is from a study that developed a way to measure these forces. 

Actin- and microtubule-based motors move many types of material around a cell to drive critical cellular events. These motor-driven movements and other active processes in the cell contribute to a background of fluctuating forces in a cell. These stochastic forces collectively drive random motion of organelles and proteins within a cell, in turn affecting the dynamics and metabolic state of a cell. To measure these forces, Guo and colleagues developed force spectrum microscopy (FSM) to directly quantify the fluctuating forces in a cell’s cytoplasm, specifically by measuring the movements of individual injected particles. Guo and colleagues found that these forces are strong enough to move both large and small components, and that malignant cells have a higher level of fluctuating forces compared to benign cells. Image above shows a cell with injected particles (green), with the 2-minute trajectories (black) superimposed.

Guo, M., Ehrlicher, A., Jensen, M., Renz, M., Moore, J., Goldman, R., Lippincott-Schwartz, J., Mackintosh, F., & Weitz, D. (2014). Probing the Stochastic, Motor-Driven Properties of the Cytoplasm Using Force Spectrum Microscopy Cell, 158 (4), 822-832 DOI: 10.1016/j.cell.2014.06.051
Copyright ©2014 Elsevier Ltd. All rights reserved.

August 21, 2014

Microtubules are known for their fascinating dynamics, but some cellular processes require a more stable microtubule cytoskeleton. Thankfully, these stable, acetylated microtubules are just as photogenic as their non-modified microtubule pals. Today’s image is from a paper describing the role of the protein paxillin in microtubule acetylation. 

Crawling cells require coordination of adhesive forces, cytoskeletal rearrangements, and cell polarization. Cell polarization helps to direct newly synthesized proteins to the leading edge of the crawling cell, relying on both a stable microtubule cytoskeleton and positioning of the Golgi apparatus in front of the nucleus. The stability of these long-lived microtubules is due to acetylation—a post-translational modification of α-tubulin. A recent study by Deakin and Turner uncovered a role for the focal adhesion scaffolding protein paxillin in regulating microtubule acetylation, which in turn regulates Golgi integrity and cell polarization. Paxillin modulates microtubule stability through its inhibition of HDAC6, an α-tubulin deacetylase, and does so in both normal and transformed cells. In the images above, depletion of paxillin (bottom) in malignant (left column) and normal (right column) cell types resulted in a drop of microtubule acetylation (yellow), compared to control cells (top).

Deakin, N., & Turner, C. (2014). Paxillin inhibits HDAC6 to regulate microtubule acetylation, Golgi structure, and polarized migration originally published in the Journal of Cell Biology, 206 (3), 395-413 DOI: 10.1083/jcb.201403039

August 19, 2014

Think of life without tubes for a moment. Not only would our huge bodies cease to exist, but our homes’ plumbing would be a mess and my 5-year old’s marble run would be pretty boring. The formation of tubes during development is a fascinating topic. Today’s image is from a paper describing the role of endocytosis in seamless tube formation.

The trachea of the fruit fly is a simple tubular system that functions as the respiratory system of the fly. The star-shaped tracheal terminal cells form seamless tubes that extend the length of long cellular extensions. Schottenfeld-Roames and colleagues recently published a study investigating the mutations in the braided gene. Tracheal terminal cells in braided mutants have tubular cysts and fewer branches, as seen in the images above (top is wild-type; bottom is mutant). braided encodes Syntaxin7, a endocytosis protein that promotes fusion of vesicles to early endosomes. Schottenfeld-Roames and colleagues found that mutations in other early endosome proteins cause similar terminal cell tube defects. Additional data showing increased levels of the apical protein Crumbs in braided terminal cells suggests that early endocytosis regulates levels of Crumbs, which in turn affects tube formation through actin cytoskeleton modulation. The images above show the luminal membrane (green) and an apical protein (magenta) in tracheal tubes. The tubes in braided mutants are cystic and abnormal, and the tube tips are disorganized (higher magnified views of the boxed regions are on the left).

Schottenfeld-Roames, J., Rosa, J., & Ghabrial, A. (2014). Seamless Tube Shape Is Constrained by Endocytosis-Dependent Regulation of Active Moesin Current Biology, 24 (15), 1756-1764 DOI: 10.1016/j.cub.2014.06.029
Copyright ©2014 Elsevier Ltd. All rights reserved.

All the images were acquired by Dr. Jodi Schottenfeld-Roames.

August 14, 2014

Astrocytes used to be the red-headed stepchild of the neurobiology world, but no more! Once considered to be just filler material, astrocytes are now known to function in the development and function of synapses, though the mechanisms are unclear. Today’s stunning image is from a paper showing how astrocytes can stabilize synapses, possibly serving as an important component of learning and memory. 

The synapses of neurons in the central nervous system are dynamic in response to learning and memory. The synapses are enveloped by perisynaptic astrocytic processes (PAPs), which are intricate processes of astrocytes. This close association of PAPs with synapses suggests an important role for astrocytes in synaptic development, transmission, and plasticity—the focus of a recent paper by Bernardinelli and colleagues. In this study, time-lapse imaging of brain slices revealed that long-term potentiation increased PAP motility and astrocyte coverage of the synapse. In vivo imaging of the somatosensory cortex of adult mice after whisker stimulation showed an increase in PAP motility, and later dendritic spine stability. From these results, Bernardinelli and colleagues identify a novel bidirectional interaction between PAPs and synapses, in which synaptic activity regulates PAP plasticity, which in turn regulates PAP coverage of synapses and long-term spine survival. The image above shows CA1 neurons (green) and stratum radiatum astroctyes (red) in mouse hippocampal tissue.

Bernardinelli, Y., Randall, J., Janett, E., Nikonenko, I., König, S., Jones, E., Flores, C., Murai, K., Bochet, C., Holtmaat, A., & Muller, D. (2014). Activity-Dependent Structural Plasticity of Perisynaptic Astrocytic Domains Promotes Excitatory Synapse Stability Current Biology, 24 (15), 1679-1688 DOI: 10.1016/j.cub.2014.06.025
Copyright ©2014 Elsevier Ltd. All rights reserved.

August 7, 2014

No matter how many brilliant discoveries are made by countless brilliant scientists, there will always be a lot of unknowns out there. These unknowns are what keep our mental wheels turning, our imaginations running, and our labs busy. Today’s image is from a paper that describes a newly-discovered process of vascular development called “canalogenesis.”

Schlemm’s canal (SC) is a flattened tube that encircles the anterior portion of the eye and drains fluid from the area. Abnormal drainage contributes to glaucoma, a disease that causes vision loss, yet a description of SC development and SC endothelial cells (SECs) is incomplete. In a recent study, Kizhatil and colleagues developed a new whole-mount procedure and used high-resolution confocal microscopy to study large regions of the SC during development. Kizhatil and colleagues found that the phenotype of SECs is a blend of blood and lymphatic endothelial cells, and that the SC develops through by a newly-discovered process called “canalogenesis.” Canalogenesis has features that are similar to, yet different from, the three well-studied vascular development programs—vasculogenesis, angiogenesis, and lymphangiogenesis. The image above was acquired using the new whole-mount procedure that protects the delicate ocular drainage structures. The SC (blue) is visualized in 3D relative to nearby blood vessels (magenta).

Kizhatil, K., Ryan, M., Marchant, J., Henrich, S., & John, S. (2014). Schlemm's Canal Is a Unique Vessel with a Combination of Blood Vascular and Lymphatic Phenotypes that Forms by a Novel Developmental Process PLoS Biology, 12 (7) DOI: 10.1371/journal.pbio.1001912

July 31, 2014

Do you ever feel nostalgic for a specific paper? Maybe this paper inspired your own research, or maybe it was a paper you immediately knew would be game-changing. Maybe, like today’s TBT paper, it was a great paper about solidly executed research with a memorable giggle-inducing technique. Thanks to a nostalgic HighMag reader and friend, Omar Quintero, we are being re-introduced to gonad sandwiches. 

In mammals, sex determination refers to the changes during early development that lead to the formation of either the testis or ovary. A gene on the Y chromosome called Sry initiates testis formation from the early bipotential gonad, including organizing Sertoli cells into the testis cord structure. In a 1997 paper, Martineau and colleagues investigated the early cell movements that occur after Sry expression, specifically the movement of nearby mesonephric cells to the genital ridge. To see these cell movements, Martineau and colleagues grafted a “blue” mesonephros from a mouse ubiquitously expressing β-galactosidase next to a “white” gonad from a different mouse. The movement of blue cells into the white gonad in these gonad sandwiches revealed that this movement is dependent on a signal induced by the male (XY) gonad that acts as a chemoattractant. Migration does not occur if an XX gonad is used in the sandwich, yet migration can occur whether an XY or XX mesonophros is used. The images above show the different XX and XY combinations used in these experiments, with XY gonads leading to extensive migration of blue cells. 

Martineau, J., Nordqvist, K., Tilmann, C., Lovell-Badge, R., & Capel, B. (1997). Male-specific cell migration into the developing gonad Current Biology, 7 (12), 958-968 DOI: 10.1016/S0960-9822(06)00415-5

Copyright ©1997 Elsevier Ltd. All rights reserved.

July 24, 2014

How many times can you say the word “gonad” in a sentence without giggling? If the answer is none, then I congratulate you on turning thirteen. If the answer is many, then you must be a biologist. Biologists appreciate the value of a good gonad, and so should you. The gonad of the worm C. elegans serves as an important model in which to study tissue organization and development, as you’ll see in the paper that accompanies today’s image.

At the end of cell division, cytokinesis typically results in two separate daughter cells. Some cytokinesis, though, is incomplete and leads to two daughter cells sharing cytoplasm. This shared cytoplasm, or syncytium, can be found in the germ cells of many species from worms to humans. The germline of the worm C. elegans is a polarized tube in which germ cells are arranged around the shared cytoplasmic core and move along a conveyer belt of oocyte production. Amini and colleagues recently reported on the formation of the syncytial C. elegans germline throughout development, and the role of the short Anillin family scaffold protein ANI-2. ANI-2 is localized to the intercellular bridges that connect the germ cells to the shared cytoplasm, and loss of ANI-2 results in destabilization of intercellular bridges and sterility. The defects seen in worms lacking ANI-2 are likely due to a loss of the stability and elasticity of the intercellular bridges that is required to compensate for the stress of cytoplasmic streaming during oogenesis. Images above show the germlines of wild-type and ani-2(-) worms at different larval stages (membranes in green; nuclei in red). Worms lacking ANI-2 have abnormal multinucleated germ cells (arrowheads).

Amini, R., Goupil, E., Labella, S., Zetka, M., Maddox, A., Labbe, J., & Chartier, N. (2014). C. elegans Anillin proteins regulate intercellular bridge stability and germline syncytial organization originally published in the Journal of Cell Biology, 206 (1), 129-143 DOI: 10.1083/jcb.201310117