Microtubule orientation controls polarized trafficking in neurons. In this work, γ-tubulin is identified as a key regulator of both axonal and dendritic microtubule polarity. In addition, the idea that γ-tubulin works in dendrites by residing at Golgi outposts is tested.

Feng et al. describe persistent neuronal microtubule minus end growth that depends on the CAMSAP protein Patronin and is needed for dendritic minus-end-out polarity.

In vertebrate neurons, the axon initial segment (AIS) is specialized for action potential initiation. It is organized by a giant 480 Kd variant of ankyrin G (AnkG) that serves as an anchor for ion channels and is required for a plasma membrane diffusion barrier that excludes somatodendritic proteins from the axon. An unusually long exon required to encode this 480Kd variant is thought to have been inserted only recently during vertebrate evolution, so the giant ankyrin-based AIS scaffold has been viewed as a vertebrate adaptation for fast, precise signaling. We re-examined AIS evolution through phylogenomic analysis of ankyrins and by testing the role of ankyrins in proximal axon organization in a model multipolar Drosophila neuron (ddaE). We find giant isoforms of ankyrin in all major bilaterian phyla, and present evidence in favor of a single common origin for giant ankyrins and the corresponding long exon in a bilaterian ancestor. This finding raises the question of whether giant ankyrin isoforms play a conserved role in AIS organization throughout the Bilateria. We examined this possibility by looking for conserved ankyrin-dependent AIS features in Drosophila ddaE neurons via live imaging. We found that ddaE neurons have an axonal diffusion barrier proximal to the cell body that requires a giant isoform of the neuronal ankyrin Ank2. Furthermore, the potassium channel shal concentrates in the proximal axon in an Ank2-dependent manner. Our results indicate that the giant ankyrin-based cytoskeleton of the AIS may have evolved prior to the radiation of extant bilaterian lineages, much earlier than previously thought.

Human papillomavirus (HPV) is a significant health burden and leading cause of virus-induced cancers. HPV is epitheliotropic and its replication is tightly associated with terminal keratinocyte differentiation making production and purification of high titer virus preparations for research problematic, therefore alternative HPV production methods have been developed for virological and structural studies. In this study we use HPV16 quasivirus, composed of HPV16 L1/L2 capsid proteins with a packaged cottontail rabbit papillomavirus genome. We have achieved the first high resolution, 3.1 Å, structure of HPV16 by using a local subvolume refinement approach. The high resolution enabled us to build L1 unambiguously and identify L2 protein strands. The L2 density is incorporated adjacent to conserved L1 residues on the interior of the capsid. Further interpretation with our own software for Icosahedral Subvolume Extraction and Correlated Classification revealed flexibility, on the whole-particle level through diameter analysis and local movement with inter-capsomer analysis. Inter-capsomer expansion or contraction, governed by the connecting arms, showed no bias in the magnitude or direction of capsomer movement. We propose that papillomavirus capsids are dynamic and capsomers move as rigid bodies connected by flexible linkers. The resulting virus structure will provide a framework for continuing biochemical, genetic and biophysical research for papillomaviruses. Furthermore, our approach has allowed insight into the resolution barrier that has previously been a limitation in papillomavirus structural studies.