Septins in Aspergillus nidulans: Organization of the Division Site and the Cell Surface

University Of Georgia Research Foundation Inc, Athens GA

Investigators

Abstract

All cells arise from existing cells. The doubling of contents and partitioning of those contents to daughter cells must be carefully controlled in all organisms. The septin family of proteins plays a central role in organizing proper growth and division of the budding yeast Saccharomyces cerevisiae and likely plays a similar role in many other eukaryotes. Septin complexes appear to function as scaffolds, recruiting and tethering other proteins to appropriate sites. Among the proteins that localize to the yeast division plane in a septin-dependent manner are enzymes responsible for cross-wall synthesis and cell cycle regulators that appear to coordinate growth with nuclear division. While most knowledge of septin function comes from elegant work in the unicellular fungus S. cerevisiae, septins have also been found in multicellular fungi and in animals. Five septin genes, aspA-aspE, have been identified in the filamentous fungus Aspergillus nidulans. In this multicellular fungus a single septin, AspBp, localizes to several different structures (septa, branches, and conidiophores). AspBp localization is post-mitotic at septa where the localization pattern changes from a single ring to a double ring back to a single ring during septal development. AspBp localization is pre-mitotic at branches where the localization pattern changes from a compact patch to a diffuse collar as branches emerge. The central hypothesis for this research is that complexes at septa, nascent branches, and conidiophores in A. nidulans contain different combinations of both septin and non-septin proteins and that membership within the same complex will vary over time as development proceeds. This hypothesis will be tested using a variety of approaches. Mutant phenotypes and localization will be examined for all five septins. Interactions among septins and between septins and other proteins will be identified using genetic and biochemical methods. Selected non-septin proteins that interact with septin complexes at septa will be localized. These studies will exploit the ability to predict and manipulate the development of septa, and to a lesser extent other structures, in A. nidulans. The proposed studies will likely lead to a better understanding of septin function in multicellular organisms and of basic processes in the development of filamentous fungi.