We hosted Pedro Pereira, Ricardo Henriques’ lab alumni now at ITQB Nova in Lisbon, for a week of intense experiments. Pedro taught us DNA-PAINT antibody coupling with great success! Thanks a lot for spending time with us despite the flu… We also said goodby to Master’s student Solène and Florian, hoping to see them again soon!
Our latest work (previously on bioRxiv) is now published in the Journal of Cell Biology. We collaborated with the Roy lab to reveal a new mechanism of slow axonal transport, based on the previous discovery of actin hotspots and trails. Hotspots are static actin clusters that appear and disappear within minutes every 3-4 µm along the axon. They generate the assembly of trails, long actin filaments that polymerize along the axon and collapse within seconds. Our new article first shows that trails polymerize at their barbed ends, located at the surface of hotspots. Each trail is thus pushed away from the hotspot as as it grows, resulting in a net displacement of actin monomers after trail collapse. In addition, trails grow in both directions (anterograde and retrograde), but with a small bias toward the tip of the axon (58% anterograde vs 42% retrograde).
The combination of these two processes (displacement of actin by trails and anterograde bias) results in the slow progress of actin along the axon. Modeling from the Jung lab allowed to determine the overall actin transport speed resulting from the hotspots and trails dynamics. Strikingly, this slow anterograde transport speed of actin (0.4 mm/day) precisely matches the values obtained by classic radio-labeling studies. This is a fundamentally new mechanism of slow axonal transport for cytoskeletal components, based on a biased assembly/disassembly mechanism rather than processive transport by motor proteins.
In this work, we used STORM imaging of axonal actin to pinpoint the architecture of hotspots, showing that the multi-directional growth of trails make them appear as asters when the axon is thicker (see Figure). Furthermore, we imaged hundreds of hotspots by STORM and quantified their diameter to ~200 nm. This is a first step toward elucidating the molecular organization of hotspots and trails, which will be crucial to understand their cellular functions.
The Spanish and Portuguese meeting for Advanced Microscopy (SPAOM) was held in Granada this year. The occasion to test a SIM microscope between two interesting talks! Thanks to Paula Sampaio and the organizers for the invitation!
Christophe was lucky to spend a whole week at the “Microscopie Fonctionnelle en Biologie” aka MiFoBio workshop. Lots of fun attending dozens of cutting-edge workshops, trying super-resolution microscopes, discussing, DJing (!), and presenting the latest work from the lab.
More on Twitter: #MiFoBio2018
Axons in the Hills was a great 2-day meeting about all things axons was organized by Maren Engelhardt, Maarten Kole, Andreas Draguhn and Paul Jenkins at the Heidelberg University. Christophe chaired the “Molecular Organization of Axons” featuring Marseille colleague Dominique Debanne, Juan Garrido and Elisa d’Este. Fun experience and great science!
Christophe was interviewed by journalist Anne Debroise of the French scientific magazine Science & Vie about a recent article from the Bock lab (Zheng et al., 2018) that provides the volume of an adult Drosophila fly brain by electron microscopy. You can read the short article here (in French, subscription required) or via the screenshot below.
We all said goodbye to Nikki who finished her Master’s internship at the end of July. Nikki is a great student, and she managed to get a PhD position in the lab of Ruud Toonen at the Center for Neurogenomics and Cognitive Research in Amsterdam. Good luck for this new adventure!