Dj. Sharp et al., EXPRESSION OF A MINUS-END-DIRECTED MOTOR PROTEIN INDUCES SF9 CELLS TOFORM AXON-LIKE PROCESSES WITH UNIFORM MICROTUBULE POLARITY ORIENTATION, Journal of Cell Science, 110, 1997, pp. 2373-2380
Neurons extend two types of processes with distinct morphologies and p
atterns of microtubule polarity orientation, Axons are thin cylindrica
l processes containing microtubules that are uniformly oriented with t
heir plus-endsdistal to the cell body while dendrites are stout taperi
ng processes that contain nonuniformly oriented microtubules, We have
proposed that these distinct microtubule patterns are established by m
olecular motors that transport microtubules into each type of process
with the appropriate orientation, To test the feasibility of this prop
osal, we have embarked on a series of studies involving the expression
of vertebrate motors in insect Sf9 cells, We previously focused on a
kinesin-related protein termed CHO1/MKLP1, which localizes to the midz
one of the mitotic spindle, and which has been shown to have the appro
priate properties to transport microtubules of opposite orientation re
lative to one another, Expression of a fragment of CHO1/MKLP1 containi
ng its motor domain induces Sf9 cells to extend processes with a stout
tapering morphology and a nonuniform microtubule polarity pattern sim
ilar to dendrites, Here we focus on a minus-end-directed kinesin-relat
ed motor protein termed CHO2, which localizes to the nonoverlapping re
gions of the mitotic spindle, and which has been shown to have the app
ropriate properties to transport microtubules with plus-ends-leading.
Sf9 cells induced to express a fragment of CHO2 containing its motor d
omain extend processes with a long cylindrical morphology and a unifor
mly plus-end-distal microtubule polarity pattern similar to axons, The
se results show that motor proteins have the capacity to organize dist
inct patterns of microtubule polarity orientation during process outgr
owth, and that these patterns are intimately related to the unique mor
phological characteristics of the processes, Moreover, mutation of thr
ee amino acids corresponding to the ATP binding site necessary for mot
or function suppresses the capacity of the CHO2 fragment to induce pro
cess formation and microtubule reorganization, indicating that at leas
t in the case of CHO2, the transport properties of the motor are essen
tial for it to elicit these effects.