since ancient Egyptian times as a 
treatment for gout, stops spindle 
formation and arrests cell division. In 
1967, Edwin Taylor and his associ- 
ates at the University of Chicago 
discovered that colchicine did its 
work by binding to tubulin. Two 
other chemicals, vinblastine and vin- 
cristine, also disrupt spindles and are 
used as anticancer drugs since they 
preferentially inhibit the spindles of 
rapidly dividing cancer cells. 
Between cell divisions, microtubules 
act as miniature highways along 
which vesicles carrying such materials 
as hormones, neurotransmitters, and 
nutrients move. Using new tech- 
niques, such as video-enhanced light 
microscopy, scientists in several labo- 
ratories have observed microtubules 
interacting with a globular protein 
called kinesin that functions as a 
molecular motor to move vesicles and 
organelles along microtubule tracks 
toward the cell surface. Kinesin also 
moves vesicles filled with neurotrans- 
mitters along the microtubules within 
nerve cell axons. A motor protein 
that moves vesicles in the opposite 
direction, toward the cell's interior, 
was discovered in 1987. 
Microtubules are also involved in 
the movement of cilia and flagella. 
These whiplike filaments project from 
certain cells and perform a variety of 
tasks. Large numbers of cilia are 
found on cells that line the respiratory 
system, for instance, where they help 
to sweep out dust and debris. Both 
cilia and flagella play an important 
role in human reproduction. The 
coordinated beating of cilia in the 
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