January 5, 2012

Despite my two-year old daughter’s observation that gummy fruit snacks are great adhesive tools, the tissues in our body require something a bit more sophisticated to stick together. Different types of tissue need different specialized adhesion structures. For example, desmosomes function in heart and skin tissue, which are under a lot of mechanical stress. Today’s image is from a paper describing how some desmosome proteins get to the adhesion site.

Desmosomes are highly-ordered structures at the plasma membrane that adhere cells to one another, and play a crucial role in maintaining tissue integrity both during and after development. The adhesion properties of desmosomes are due to the presence of two different cadherin proteins, called Dsg and Dsc. A recent paper describes how these two cadherins are trafficked to desmosome adhesion sites. According to Nekrasova and colleagues, Dsg and Dsc are transported to desmosomes by two different kinesins, which are motors that walk along microtubules. Dsg is transported by kinesin-1, while Dsc is transported by kinesin-2. That each desmosome cadherin has its own transport pathway suggests that the assembly and function of desmosomes, and in turn adhesion, can be tailored throughout development and tissue remodeling. In the sequence of images above, Dsg (red, arrow) is migrating along microtubules (blue) towards the cell periphery.

Nekrasova, O., Amargo, E., Smith, W., Chen, J., Kreitzer, G., & Green, K. (2011). Desmosomal cadherins utilize distinct kinesins for assembly into desmosomes originally published in The Journal of Cell Biology, 195 (7), 1185-1203 DOI: 10.1083/jcb.201106057

October 3, 2011

Behind every great mobile organelle is an equally awesome motor protein. The motor proteins dynein and kinesin move cargo along microtubules, and play crucial roles in countless cellular processes. A recent paper shows how these two motors cooperate.

The fungus Ustilago maydis grows into long hyphal cells in laboratory culture. Their use in cell biology is powerful, as their length and motor transport is reminiscent of human neurons. These long cells grow from the cell tip and have similarly oriented microtubules at either end of the cell. In the middle of the cell, microtubules overlap with opposite polarity. The polarity of these microtubules is important – dynein motors walk to one end of microtubules (the “minus” end), while most kinesin motors walk to the other (the “plus” end). A recent paper looked at how these two motors cooperate with each other in the motility of early endosomes in U. maydis cells. Schuster and colleagues found that while dynein is important for short-range motility, kinesin is important for long-range transport through the antipolar microtubule array in the center of the cell. Top image above shows the elongated hyphal cell with the nucleus in red. Bottom image shows the growth of microtubules by showing two consecutive time-points of EB1 (red then green), which is a protein found on the tips of growing microtubules. The two different insets show the antipolar growth of microtubules at the center (left inset), compared with the growth of similarly-oriented microtubules near the cell tip (right inset).

Schuster, M., Kilaru, S., Fink, G., Collemare, J., Roger, Y., & Steinberg, G. (2011). Kinesin-3 and dynein cooperate in long-range retrograde endosome motility along a nonuniform microtubule array Molecular Biology of the Cell, 22 (19), 3645-3657 DOI: 10.1091/mbc.E11-03-0217

March 4, 2010

Microtubules are important cytoskeletal structures that can be modified in ways that allow for specific cellular functions. Kinesins are microtubule motors, and a recent study has tested how different kinesins move along microtubules modified in different ways. For example, one kinesin will only walk along stable microtubules, while two other kinesin motors are not so selective. The image above shows a Kinesin-2 family member (left) moving along all microtubule tracks (middle) in a cell.

Reference: Dawen Cai, Dyke P. McEwen, Jeffery R. Martens, Edgar Meyhofer, Kristen J. Verhey. Their PLoS Biology paper can be found here.