The dynamic cytoskeleton of the filamentous fungus Ashbya gossypii.
Philippe Laissue (1), Hans-Peter Schmitz (2), Philipp Knechtle (1), Peter Philippsen (1)
(1) Angewandte Mikrobiologie, Biozentrum, Universitaet Basel, Klingelbergstr.50/70, Basel, CH-4056, Switzerland; (2) Universität Osnabrück , AG Genetik, Barbarastr. 11 , D-49076 Osnabrück, Germany
Ashbya gossypii is a filamentous fungus with homologs of all S. cerevisiae genes responsible for the organisation and function of the actin cytoskeleton. But the requirements for filamentous growth are different compared to the alternating phases of polar and isotropic growth in budding yeast. We analyse the actin cytoskeleton of A. gossypii studying its GFP-tagged components with rapid, multi-dimensional video microscopy, revealing similar dynamic parameters and probable functional differences. GFP-labelled capping protein was used for studying actin patches. Cap1-GFP and Cap2-GFP patches are highly enriched in the first six micrometers from the tip, mostly cortical, and at sites of septation and branch formation. The patches move at 224 (+/-98) nm/s over distances of 0.8um (+/-0.7um) and generally have a lifetime of 14 seconds (+/-6.5). Net movement is away from the tip. A second movement type is that of retrograde patches returning to the tip. Co-stainings with the endocytosis marker FM4-64 show partial colocalization. Application of Latrunculin A results in depolarized, spherical tips. Actin cables and actin rings were visualized with Abp140p-GFP. Abp140p-GFP cables are cortical, often helical, highly motile and up to 40um long. Elongation of the tip of a cable is 184 (+/-62) nm/s. Fine cables in the apical zone show Abp140p-GFP patches moving to the tip, where they disintegrate. We conclude with a model of the hyphal organisation of the actin cytoskeleton in A. gossypii.