We have followed the migration of GFP-labelled nuclei in multinucleate hyphae of 
Ashbya gossypii. For the first time we could demonstrate that the mode of long 
range nuclear migration consists of oscillatory movements of nuclei with, on 
average, higher amplitudes in the direction of the growing tip. We could also 
show that mitotic division proceeds at a constant rate of 0. 64 microm/minute 
which differs from the biphasic kinetics described for the yeast Saccharomyces 
cerevisiae. Furthermore we were able to identify the microtubule-based motor 
dynein as a key element in the control of long range nuclear migration. For 
other filamentous fungi it had already been demonstrated that inactivating 
mutations in dynein led to severe problems in nuclear migration, i.e. generation 
of long nuclei-free hyphal tips and clusters of nuclei throughout the hyphae. 
This phenotype supported the view that dynein is important for the movement of 
nuclei towards the tip. In A. gossypii the opposite seems to be the case. A 
complete deletion of the dynein heavy chain gene leads to nuclear clusters 
exclusively at the hyphal tips and to an essentially nucleus-free network of 
hyphal tubes and branches. Anucleate hyphae and branches in the vicinity of 
nuclear clusters show actin cables and polarized actin patches, as well as 
microtubules. The slow growth of this dynein null mutant could be completely 
reverted to wild-type-like growth in the presence of benomyl, which can be 
explained by the observed redistribution of nuclei in the hyphal network.