Matthew T Swulius has completed his PhD at University of Texas Health Science Center at Houston in 2010, where he studied structural and protein compositional changes in the synapse throughout development. He is currently a senior Post-doc in Grant Jensen’s lab at Caltech, where he has contributed to the field of bacterial cell biology by studying the MreB cytoskeleton using electron cryotomography and to eukaryotic cell division using cryo-focused ion beam milling and correlated light and electron microscopy to image the native structure of the actomyosin ring in fission yeast.


While electron cryotomography (ECT) is a powerful technique for imaging unique biological structures to molecular resolution, some protein machinery is complex and highly dynamic, making static images difficult to interpret on their own. In such cases, coarse-grained simulations can be employed in order to interpret and test the mechanistic implications of such experimental data. Here we use a combination of ECT and simulation to study the structure and contractile mechanism of the actomyosin ring (AMR) in fission yeast. Because fission yeast are beyond the thickness amenable to cryoEM, we used cryo-focused ion beam milling and cryosectioning to gain access to natively preserved AMRs. ECT revealed bundles of actin filaments running parallel to one another that were “saddling” the leading edge of the septum, and no direct contact between actin and the membrane was observed, refuting the notion that F-actin is connected to the membrane at cytokineteic nodes. After exploring a variety of actomyosin configurations by 3D coarse-grained simulation, we propose a model that best agrees with our and other published experimental data.