Full disclosure: today’s image is near and dear to me. Today’s image is from a paper written by members of my former graduate lab, with some very close friends as the co-first authors. This is not to say that this paper isn’t utterly fascinating with sparkling images and fantastic experiments designed by some of the brightest scientists around (enough superlatives for you?), because it is all of the above and more. I’m just disclosing my bias so if today’s post sounds like a love letter, you’ll let it slide.
During development, it is necessary for cells to change their shape—it allows cells and sheets of cells to form into specific structures and tissues. Apical constriction drives cell shape changes in many cell types by contracting the actin-myosin network on the apical side of the cell, causing that side of the cell to shrink. After apical constriction, cells are shaped more like wedges, and a whole sheet of apically constricting cells can result in dramatic changes. For example, apical constriction drives the folding and closing of neural plate cells to form the neural tube, which later becomes our brain and spinal cord. A recent paper looks at apical constriction during gastrulation in the worm embryo, at the start of which two cells on the outside of the embryo apical constrict and are internalized into the middle of the embryo. Roh-Johnson and colleagues found that the actin-myosin networks were dynamic and contracting long before the cells showed any type of shape change, functioning as a molecular “clutch.” The cells were internalized only after the actin-myosin contractions appeared to have been mechanically linked to the cell-cell contact zone. Roh-Johnson and colleagues found this same molecular clutch in apically constricting cells in the developing fruit fly, suggesting that this mechanism might be a key component of apical constriction across the board. The images above show two timepoints of a worm embryo in the process of internalizing the two cells at the start of gastrulation (bottom image is about 6 minutes after the top image). Green is myosin, red is membranes, and blue marks the surfaces of the internalizing cells. Image credit: Chris Higgins and Liang Gao.
BONUS!! Check out a fancy little blurb about this paper in The Scientist here (complete with movie!).
BONUS!! Do you like worms? Of course you do! Mosey over to the Goldstein Lab’s site for more movies here.
Roh-Johnson, M., Shemer, G., Higgins, C., McClellan, J., Werts, A., Tulu, U., Gao, L., Betzig, E., Kiehart, D., & Goldstein, B. (2012). Triggering a Cell Shape Change by Exploiting Preexisting Actomyosin Contractions Science DOI: 10.1126/science.1217869