EXPRESSION OF A MINUS-END-DIRECTED MOTOR PROTEIN INDUCES SF9 CELLS TOFORM AXON-LIKE PROCESSES WITH UNIFORM MICROTUBULE POLARITY ORIENTATION

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.