The test began with researchers putting fluorescent actin in fruit fly muscle cells that incorporated themselves into the growing actin branches in the finger-like protrusions. Then, the researchers used a laser beam to bleach the fluorescent actin in the region of the finger-like protrusions and waited to see whether and how long it would take for new, unbleached actin to spread from other parts of the cell and be taken up by the growing branches in the "fingers." In normal muscle cells, it took about two minutes for the fluorescence to return. In muscle cells that lacked Blown Fuse, the fluorescence never fully recovered and the cytoskeleton failed to project finger-like protrusions, probably because the WASP-WIP complex does not come off the ends of the actin filaments to start new actin branches.
"These results suggest that the growing ends of the actin cytoskeleton are occupied by the WASP-WIP protein duo and that without Blown Fuse to dissociate with the WASP-WIP complex and push WASP off the ends, new actin branches cannot be started," says Chen. "And these shorter and stiffer new branches are critical for generating the finger-like membrane protrusions."
Through a microscope, the Hopkins team compared the finger-like projections from normal cells with cells lacking Blown Fuse. Normal muscle cells form pointy finger-like protrusions that push into the other muscle cell, but cells without Blown Fuse have fewer and floppier protrusions that don't push t
|Contact: Vanessa McMains|
Johns Hopkins Medical Institutions