ORGANIZATION OF ACTIN AND MICROTUBULES DURING PROCESS FORMATION IN TAU-EXPRESSING SF9 CELLS

Insect Sf9 cells usually elaborate a highly characteristic single proc ess when infected with a baculovirus encoding recombinant human tau. T he processes are unbranched, of uniform caliber, and contain bundles o f microtubules. Because taxol treatment alone does not induce process outgrowth in these cells, it is believed that tau confers properties o n microtubules that permits the conversion of microtubule assembly int o the formation of processes. Here we have analyzed the reorganization of both actin filaments and microtubules during process initiation. A zone of organelle exclusion representing the focal reorganization of actin at one pole of the Cell anticipated process emergence. A relatio nship between actin organization and process emergence was also sugges ted by a shift from single to multiple process formation after treatme nt with cytochalasin D. The rate of process elongation doubled after c ytochalasin treatment of tau-expressing cells. The increase in rate wa s due to the inhibition of the growth arrest phases which occur in the absence of cytochalasin. In contrast, Sf9 cells treated with cytochal asin after more than 20 h of tau expression were relatively resistant to the drug's effects. We conclude that actin and microtubules are spe cifically reorganized during tau-induced process outgrowth and that a dynamic relationship between actin filaments and microtubules effects process formation. (C) 1994 Wiley-Liss, Inc.