November 26, 2014

 

Patterns are soothing for left-brained folks like me, with the exception being those terrible patterned holiday sweaters that will come out of mothball-ridden closets soon (unsettling for everyone, really). Today’s images are from a paper describing a new micropatterning technique to look at plasma membrane proteins. 

The plasma membrane of a cell is riddled with many multi-protein complexes that facilitate communication and transport. These complexes provide a challenge to biologists due to their ubiquitous localization around the cell, their large, complex size, and their transient interactions with proteins. A recent paper describes a technique to study signaling complexes at the plasma membrane, using micropatterns within the plasma membrane. Löchte and colleagues expressed a protein bait in a micropattern in a living cell’s plasma membrane. Dynamics of the interactions between the protein bait and ligand target can then be quantified using live microscopy and on a single-molecule level. Löchte and colleagues used the IFN interferon signaling complex, using one of the receptor units (IFNAR2) as bait. In the top images above, the micropatterned receptor bait (IFNAR2) was able to recruit the other IFN receptor subunit (IFNAR1, green) after the addition of the ligand (red; time represents the addition of the ligand). Bottom image shows a closer view of the high-affinity, micropatterned binding that requires simultaneous interaction of the ligand (red) with both receptor subunits.


Lochte, S., Waichman, S., Beutel, O., You, C., & Piehler, J. (2014). Live cell micropatterning reveals the dynamics of signaling complexes at the plasma membrane originally published in the Journal of Cell Biology, 207 (3), 407-418 DOI: 10.1083/jcb.201406032

March 26, 2013

When Outkast sang that “I like the way you mooove,” I immediately figured they were talking my dancing skills.  Turns out, they were really singing about motile cells…true story*.  Today’s image is from a paper showing a link between the chemical signals that tell a cell to move and how the cell actually moves.

As an axon searches for its synaptic target, it sends out a motile extension called a growth cone.  The chemical cues that initiate mobility in the growth cone trigger major cytoskeletal rearrangements at the leading edge, specifically actin filament polymerization and an engagement with the underlying extracellular substrate.  A recent paper describes the signaling that links the chemical cues to the generation of traction forces that move the growth cone forward.  Toriyama and colleagues show that the protein shootin1 is phosphorylated following signaling from the chemoattractant netrin1.  Phosphorylated shootin1, then, triggers actin-extracellular substrate coupling and generates the forces for axonal outgrowth.  In the images above, phosphorylated shootin1 (green) is enriched at filopodial and lamellipodial extensions in growth cones (actin filaments are in red).

*not really

Toriyama, M., Kozawa, S., Sakumura, Y., & Inagaki, N. (2013). Conversion of a Signal into Forces for Axon Outgrowth through Pak1-Mediated Shootin1 Phosphorylation Current Biology, 23 (6), 529-534 DOI: 10.1016/j.cub.2013.02.017 
Copyright ©2013 Elsevier Ltd. All rights reserved. 

March 1, 2013

There are a handful of major signaling modules in development, and I’m fascinated every time a paper comes out showing a new role for one of these pathways, or how multiple pathways interact.  I admire the resourcefulness of cells in using a limited number of proteins to get an unlimited number of things done.  Today’s image is from a paper showing the role of PCP signaling in primary cilia assembly.

The PCP (polar cell polarity) signaling pathway is important in establishing cell polarity throughout development.  PCP signaling has also been linked to the formation and function of cilia, microtubule-based organelles, and a recent study investigates the mechanism between the two.  Primary cilia are solitary cilia that reside on most vertebrate cells and function in signaling, and Zilber and colleagues found that Fuzzy, a PCP signaling effector protein, is involved in primary cilium formation.  Fuzzy localizes to the basal body of cilia, and is necessary to drive Golgi-derived vesicles to the primary cilium.  Fuzzy regulates the localization of Dishevelled, a core PCP protein, to the basal body, and without Fuzzy, PCP signaling is inhibited (while activating the canonical Wnt pathway).  The images above show migrating mammalian cells at the edge of a wound in control (left) and Fuzzy mutant cells (right).  Wound-healing is controlled by PCP signaling in vertebrates, but the role of Fuzzy was unknown.  In control cells, the Golgi network (green) is polarized in front of the nucleus in most migrating cells.  In Fuzzy mutants, the Golgi network is oriented randomly in most cells (asterisks), and cell migration covered less of the initial wound area than in control cells (direction of migration indicated by white arrow).

Zilber, Y., Babayeva, S., Seo, J., Liu, J., Mootin, S., & Torban, E. (2013). The PCP effector Fuzzy controls cilial assembly and signaling by recruiting Rab8 and Dishevelled to the primary cilium Molecular Biology of the Cell, 24 (5), 555-565 DOI: 10.1091/mbc.E12-06-0437

October 8, 2012

If you are a developmental biologist, there is a high probability that you study Wnt. The Wnt signaling pathway is employed throughout cell and developmental biology in processes ranging from spindle positioning to stem cell fate decisions. Today’s image is from a paper showing how Wnt can be secreted from cells.

Wnt signaling functions by relaying a signal from the cell’s surface to the nucleus, where gene expression is regulated. Active Wnt proteins are secreted out of a cell to induce tissue patterning during development (among many other things), and can travel over a distance of several cells. In trying to understand Wnt secretion, a recent paper describes results showing that active Wnt signals can be secreted from exosomes. Exosomes are vesicles that cells use to secrete various materials into the extracellular space. Gross and colleagues found that Wnt signals are secreted on exosomes in both developing fruit flies and human cells. Wnt signals are trafficked through various endosomal compartments and then to exosomes, with the help of the trafficking protein Ykt6 (an R-SNARE). In the top row of images above, Wnt (left column, red in merged) appears colocalized with an exosomal protein (CD63, green in merged) in developing fly wing discs. Wnt is also colocalized with a marker for multivesicular bodies (LAMP-1, green in merged), vesicles from which exosomes originate.  Insets show higher magnification views of the vesicles. 

Gross JC, Chaudhary V, Bartscherer K, & Boutros M (2012). Active Wnt proteins are secreted on exosomes. Nature cell biology, 14 (10), 1036-45 PMID: 22983114

Adapted by permission from Macmillan Publishers Ltd, copyright ©2012