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