Tau is required for neurite outgrowth and growth cone motility of chick sensory neurons

The role of the microtubule-associated protein (MAP) tau in axon growth rem ains controversial. Antisense experiments have suggested that tau is requir ed for axon outgrowth, whereas genetic knockout and immunodepletion studies have suggested that tau plays no role in this process. To investigate the role of tau in both neurite outgrowth and growth cone motility, we have use d a different approach, the chromophore-assisted laser inactivation (CALI) of tau in chick dorsal root ganglion (DRG) neurons in culture. This approac h generates an acute loss of tau function that is not subject to compensati on by other MAPs. Inactivation of tau in whole DRG neurons (including cell body and neurites) reduced neurite number and length. Inactivation of tau w ithin regions of growth cones using micro-scale CALI caused a decrease in n eurite extension rate by approximately 2-fold. Surprisingly, it also caused a similar to 20% decrease in the lamellipodial size within the inactivatio n region, whereas the filopodial motility was not affected. These results s uggest that tau is required in neurite outgrowth and that tau also function s in lamellipodial motility at the growth cone leading edge. Cell Moth. Cyt oskeleton 43:232-242, 1999. (C) 1999 Wiley-liss, Inc.