EXPRESSION OF A KINESIN-RELATED MOTOR PROTEIN INDUCES SF9 CELLS TO FORM DENDRITE-LIKE PROCESSES WITH NONUNIFORM MICROTUBULE POLARITY ORIENTATION

The microtubules (MTs) within neuronal processes are highly organized with regard to their polarity and yet are not attached to any detectab le nucleating structure. Axonal MTs are uniformly oriented with their plus ends distal to the cell body, whereas dendritic MTs are of both o rientations. Here, we sought to test the capacity of motor-driven MT t ransport to organize distinct MT patterns during process outgrowth. We focused on CHO1/MKLP1, a kinesin-related protein present in the midzo nal region of the mitotic spindle where MTs of opposite orientation ov erlap. Insect ovarian Sf9 cells induced to express the N-terminal port ion of the molecule form MT-rich processes with a morphology similar t o that of neuronal dendrites (Kuriyama et al., 1994). Nascent processe s contain uniformly plus-end-distal MTs, but these are joined by minus -end distal MTs as the processes continue to develop. Thus, this CHO1/ MKLP1 fragment establishes a nonuniform MT polarity pattern and does s o by a similar sequence of events as occurs with the dendrite, the ant ecedent of which is a short process with a uniform MT polarity orienta tion, Two lines of evidence suggest that these results are elicited by motor-driven MT transport. First, there is a depletion of MTs from th e cell body during process outgrowth. Second, the same polarity patter n is obtained when net MT assembly is suppressed pharmacologically dur ing process formation. Collectively, these findings provide precedent for the idea that motor-driven transport can organize MTs into distinc t patterns of polarity orientation during process outgrowth.