Abstract
Septins are highly conserved in animals and fungi and are increasingly recognized to play roles as important and diverse as those of actin and microtubules. Septin roles include acting as diffusion barriers and coordinating cytokinesis and nuclear division. Defects in septins have been associated with human diseases including several cancers and Alzheimer’s.
Like other cytoskeletal elements, septins associate into filaments and higher-order structures. Unlike other cytoskeletal elements, septin filaments are nonpolar, assembling from both ends with no clear growing or shrinking pole. Septins are classified into five orthologous groups. Monomers from different groups associate to form nonpolar heteropolymeric rods that in turn assemble into higher-order structures including rings and filaments that can be visualized by fluorescent microscopy of GFP-tagged septins. The mechanisms driving septin heteropolymer and higher-order structure assembly are only beginning to be understood.
The filamentous fungus Aspergillus nidulans is an excellent model for understanding septins in multicellular organisms. It has one septin from each phylogenetic group. Four of the A. nidulans septins are orthologs of the core septins found in budding yeast and animals. The fifth septin, AspE, is lacking in unicellular yeasts and animals, but is found in some ciliates and algae and so appears to be ancestral. We have examined septins from defined developmental stages of A. nidulans using gene deletion, GFP-tagging with live cell imaging and immunoprecipitation. Our results show that at least two distinct septin heteropolymer populations co-exist in A. nidulans, and that while AspE is not a subunit of either heteropolymer, it is required for assembly of septin higher-order structures found in multicellular development.
Bio
Michelle Momany’s research focuses on polarity, secretion and the cytoskeleton, especially the septin cytoskeleton. She cloned the first septin from a filamentous fungus and her lab was among the first to show commonalities in septins from animals and fungi. She discovered the first noncore septin, the prototype for many septins not found in budding yeast or animals. Recently her lab has focused on interactions among septins and how these lead to higher-order structures.
Dr. Momany earned her B.A. in Microbiology from the University of Texas at Austin, USA. Her Ph.D. was in medical mycology with Paul Szaniszlo at UT, Austin and her postdoc was with John Hamer in fungal genetics at Purdue University, USA. She is Chair of the Aspergillus Genomics Research Policy Committee and past Chair of the Gordon Research Conference on Cellular and Molecular Fungal Biology and of the 28th Fungal Genetics Conference. She is an American Association for the Advancement of Science Fellow, a National Academies Education Fellow in the Life Sciences, and professor at the University of Georgia, USA.