Abstract #84C

Incomplete cytokinesis in the filamentous yeast Ashbya gossypii. Andreas Kaufmann, Juliet Odathekal, Hans-Peter Schmitz, Peter Philippsen. Biozentrum, University of Basel, Switzerland.
   Cytokinesis in Saccharomyces cerevisiae occurs by the action of over twenty components including those of the actomyosin system. Although homologs of all these genes are present in the genome of the filamentous ascomycete A. gossypii, cytokinesis does not occur in its multinucleated hyphae. Here we analyze the order of events that take place during septation in A. gossypii. Based on data from S. cerevisiae and A. gossypii we chose some cytokinetic key players to be investigated, i.e. actin, AgHof1, type II myosin, verprolin, AgCyk3, tropomyosin, formins, septins, AgBud3, and IQGAP. We determined their role in cytokinesis, their interdependencies, as well as their dynamic localization patterns. Intriguingly, Aghof1D mutants are viable but lack septa. However, septins still localize to presumptive sites of septation but actin ring formation is abolished. The absence of actin rings stands in clear contrast to results from budding yeast where actin rings are formed in mutants lacking ScHof1. 4D analyses of AgHof1-GFP dynamics reveal its localization as a collar of cortical bars at presumptive sites of septation. These bars condense to a single ring that colocalizes with the actin ring. The AgHof1 ring contracts as the septum is formed. Ring persistence is extended and contraction slower compared to S. cerevisiae. After ring contraction AgHof1 localizes to both sides of the chitin-rich septa. These studies allow us to divide the process of septation in A. gossypii into five different stages: Site selection, septins and landmark proteins localize as cortical bars and serve as guides for adaptor proteins (like AgHof1). Bar-to-ring transition, septin bars condense to double rings that delimit the adaptor proteins, which form single rings. Contractile ring assembly, actin and type II myosin localize to the single ring. Ring contraction, the actomyosin ring contracts and the septum is deposited. Septum maturation, the proteins involved in septation delocalize from the septum while the septum is strengthened. Finally, we have begun screening for proteins that prevent cell separation.

Return to YGM 2006 Home at SGD