Stories of Cells

Microtubules nose around adhesions deliver proteins that could influence adhesion turnover. The tips of multiple microtubules polymerized toward adhesions along what appeared to be tracks on the membrane. Kaverina has previously shown that tension promotes microtubule polymerization. Kaverina and Small currently hypothesize that the tracks represent tension-sensitive actin filaments that stimulate microtubule growth. They are currently looking for adaptor proteins, possibly a noncon-ventional myosin, that link microtubule tips and actin. NL rina Kaverina and Victor Small (Austrian Academy of Sciences, Austria) reveal that microtubules get up-close and personal with surface adhesions in migrating cells. The importance of microtubules for cell polarity and migration has been previously demonstrated by Small's group. Using conventional fluorescence techniques, Kaverina and Small have shown that microtubules are targeted to actin-based substrate adhesion sites. This targeting is essential during cell migration because it somehow relaxes adhesions, in particular at the rear to promote tail retraction. In the absence of microtubules, strong cell contact sites form evenly around the cell edge, inhibiting directional migration. Migration can be restored by relaxing adhesions on one side of a cell using a myosin inhibitor. The group has now taken a closer look at microtubule– adhesion interactions. Total internal reflection fluorescence microscopy shows that microtubules make frequent, repetitive trips to within nanometers of an adhesion, close enough to I Kinesins for moving chromosomes fter all the years of searching, could the hunt for an anaphase motor be over? Greg Rogers did not make such a direct claim, but the possibility was the unspoken subtext of his talk about Kin I kinesins in flies. These unusual kinesins can barely lay claim to being motors—their primary activity is to degrade microtubule ends rather than to walk over intact micro-tubules. But the mitotic spindle has been increasingly portrayed as a restless structure where tubulin subunits are constantly coming and going from microtubule ends. Now, Rogers and David Sharp (Albert Einstein College of Medicine, Bronx, NY) are proposing that the turnover of microtubules by Kin I kinesins is responsible for the majority of chromosome movement in anaphase. The destruction in question occurs at both kinetochores and spindle poles. Chewing of microtubules at spindle poles pulls microtubules toward the pole in a movement termed flux. And chewing at the kinetochore results in a Pac-Man movement of chromosomes along microtubules. Rogers used antibody injection to knock A out the function of two Kin I kinesins in fly …