April 10, 2014

When you host a party at your home, do you hire a caterer to bring in food or do you cook the food right there in your kitchen? One of these options leaves a lot more wiggle room for last-minute changes—a few extra guests, a gluten allergy, a pregnant lady with a disgust for wobbly desserts. A cell recognizes this distinction too. When making certain proteins, a cell will synthesize proteins where and when they’re needed. Today’s image is from Natasha Gutierrez, who recently published a study describing the role of β-actin mRNA and monomer synthesis in adherens junction assembly.

The actin cytoskeleton is made of actin filaments and countless actin-regulating proteins that guide the ever-changing dynamics of the cytoskeleton. Actin filament polymerization is regulated by localized synthesis of β-actin monomers from β-actin mRNA. A recent paper by Gutierrez and colleagues shows that the assembly of adherens junctions (AJs), epithelial cell-cell adhesion structures, requires localized β-actin monomer synthesis, the β-actin 3’ UTR and β-actin mRNA zipcode sequence at cell-cell contact sites. Additionally, active RhoA, which targets zipcode-mediated β-actin mRNA localization, is localized to cell-cell contact sites. In the unpublished images above, mammalian cells were treated with increasing levels (top to bottom) of a Rho inhibitor. The ability to form AJs, seen as the colocalization of actin filaments (left, green in merged) and E-cadherin (middle, red in merged) at cell-cell contact sites, decreased with increasing levels of the Rho inhibitor.

Gutierrez, N., Eromobor, I., Petrie, R., Vedula, P., Cruz, L., & Rodriguez, A. (2014). The B-actin mRNA zipcode regulates epithelial adherens junction assembly but not maintenance RNA DOI: 10.1261/rna.043208.113

December 10, 2012

A cell is nothing if not thorough. A cell can regulate a function with one method, but usually employs several methods of regulation to get a job done, ensure that it gets done correctly, and has a backup plan if it goes awry. Today’s image is from a paper describing regulation of a protein by localized levels of mRNA.

For some types of cells, notably polarized cells, the localization of a protein can be regulated through mRNAs. mRNAs are transcribed from DNA, and then later translated into the proteins that function throughout the cell. By transporting mRNAs to specific regions, the cell in turn can have localized levels of proteins. A recent paper shows the specific localization of an mRNA encoding the signaling molecule MKK7 to neuronal growth cones, which are dynamic extension of a developing axon searching for its final target. According to Feltrin and colleagues, this localization of MKK7 mRNA may result in localized levels of MKK7 protein. MKK7 mRNA localization modulates JNK signaling, which in turn regulates microtubule bundling during neuronal outgrowth. In the images above, cells with reduced levels of MKK7 mRNA (bottom) have curled and bent microtubules (red in merged, black in right panels), compared to control cells (top).

Daniel Feltrin, Ludovico Fusco, Harald Witte, Francesca Moretti, Katrin Martin, Michel Letzelter, Erika Fluri, Peter Scheiffele, & Olivier Pertz (2012). Growth Cone MKK7 mRNA Targeting Regulates MAP1b-Dependent Microtubule Bundling to Control Neurite Elongation PLOS Bio, 10 (12) : 10.1371/journal.pbio.1001439