"The Golgi apparatus is very close to the centrosome," said Kaverina. "So if you're not looking at it precisely, it is hard to distinguish between the centrosome and Golgi."
To get a close look, Kaverina and colleagues tagged the growing ("plus") ends of microtubules in human retinal epithelial cells with a fluorescent molecule, videotaped their growth and carefully followed the tracks back to their origin.
"We show that not only the centrosome, but the Golgi also makes microtubules," Kaverina said. "And unlike centrosomal microtubules, which are radial and symmetric, these microtubules are directional."
They found that microtubules originating at the Golgi are directed toward the cell "front," or the leading edge, of motile cells. Since such an orientation is needed for directional migration, Kaverina hypothesizes that this subset of microtubules may influence cell motility by facilitating the transport of proteins needed for movement to the cell front.
"This new microtubule subset that we discovered directly connects the Golgi to the cell front, so it would be very logical if these microtubules act as â€˜tracks' for this delivery," she said.
In addition to identifying this novel site of microtubule nucleation, Kaverina and colleagues also examined the molecular mechanisms governing the process. They found that proteins normally associated with the plus ends of microtubules, called CLASPs, localize to a specific compartment of the Golgi (the Trans Golgi Network) and stabilize the microtubule "seeds" at the Golgi.
Golgi-originating microtubules could also be an important factor influencing how cancer cells invade distant tissues.
Because microtubules play a central
Source:Vanderbilt University Medical Center