In vivo analysis of septin heteropolymer rods and higher-order structures in filamentous fungi

Individual septins from separate phylogenetic groups assemble into heteropolymer rods with defined compositions. Heteropolymer rods can in turn assemble into larger higher-order structures (HOS). Using a combination of immunoprecipitation and fluorescence microscopy in Aspergillus nidulans wild-type and septin-mutant strains, we have shown that even when septin HOS are not visible by fluorescence microscopy, heteropolymer rods can still be present and that a septin found largely in filamentous fungi is required for a subset of HOS. We raise several factors that are important for analysis of heteropolymer rods and HOS.