Christophe was in Finland this week, first in Turku invited by Guillaume Jacquemet, then in Helsinki to serve as an opponent for Amr Abouelezz, a brillant PhD student from Pirta Hotulainen’s lab. The PhD defense is a serious affair in Finland and Amr passed with flying colors! Thanks to Pirta for this opportunity.
You can read the PhD work of Amr in two published article: one here on the resistance of the axon initial segment actin rings to actin depolymerizing drugs, and his main work here on the presence and role of tropomyosin at the AIS. Congrats Amr!
Our latest preprint is out, a collaboration with our long-standing collaborator Subhojit Roy and his lab, in particular the talented postdoc Archan Ganguly. We uncover how clathrin is transported along axons as assembled structures that are unrelated to endocytosis: the “transport packets”. In this work, we pushed DNA-PAINT to image these axonal clathrin packets. Here they are by EM of APEX-clathrin on top and by DNA-PAINT of endogenous clathrin at the bottom. We also repurposed the ChimeraX software to render PAINT data and see inside axons!
Where are the packets going? Inside presynapses! We visualized clathrin in presynapses – 3D DNA-PAINT could clearly separate presynaptic and postsynaptic clusters. With ChimeraX we rendered and measured these presynaptic clathrin packets – similar in size to the ones along axons.
Check the preprint for the whole story – there’s so much more in there. Great work from Florian and Ghislaine in the team, congrats everyone!
Ganguly A, Wernert F, Phan S, Boassa D, Das U, Sharma R, Caillol G, Han X, Yates JR, Ellisman M, Leterrier C, Roy S. Mechanistic Determinants of Slow Axonal Transport and Presynaptic Targeting of Clathrin Packets. bioRxiv, 2020 Feb 20. doi: 10.1101/2020.02.20.958140
We have a new preprint out! This is a collaboration led by the lab of Steven F. Lee in Cambridge. They developed a new platform, vLUME (short for VisuaLization of the Universe in a Micro Environment) that allows to interact with localization-based microscopy data in a virtual reality environment. Learn more about it in this video:
Spark A, Kitching A, Esteban-Ferrer D, Handa A, Carr A, Needham L, Ponjavic A, Santos M, McColl J, Leterrier C, Davis S, Henriques R, Lee S. vLUME: 3D Virtual Reality for Single-molecule Localization Microscopy bioRxiv, 2020 Jan 21. doi: 10.1101/2020.01.20.912733
Christophe wrote a Spotlight in the Journal of Cell Biology highlighting a nice recent paper from the group of Pei-Lin Cheng in Taiwan. In this article, Lee et al. showed how degradation of the chloride transporter NKCC1 by proteasomes anchored at the AIS have a key role in lowering the intracellular chloride concentration, leading to the perinatal reversal of GABA effect from excitatory to inhibitory.
We performed super-resolution microscopy of several of the newly identified AIS components. IN particular, we showed that Mical3, a protein linking microtubules and actin, forms clusters along the AIS that are not periodically organized along the actin/spectrin scaffold.
If you speak French, you can listen to “La Méthode Scientifique”, a program on the France Culture radio which highlighted our recent article about the ultrastructure of the periodic axonal actin scaffold. Here’s the clip with an interview of Christophe:
Our work on the ultrastructure of the periodic actin/spectrin scaffold along axons is out in Nature Communications. It’s a collaboration with platinum-replica electro microscopy specialist Stephane Vassilopoulos from the Myologie Institute in Paris.
In this work that was made available as a preprintback in May, we used ultrasonic unroofing to expose the submembrane cytoskeleton along axons in neuronal cultures. This allowed to observe it both by optical super-resolution microscopy and by platinum-replica electron microscopy, zooming down to individual proteins and actin filaments.
We could visualize for the first time by EM the periodic submembrane scaffold along axons, formed of actin rings connected by spectrin tetramers. Moreover, we discovered that actin rings are not made of small actin filaments bundled together as previously assumed, but by braids of long filaments that are likely to result in their stability and flexibility. Finally, we directly visualized elements of the periodic scaffold (actin, spectrins, myosin, ankyrin) using correlative super-resolution microscopy and platinum-replica electron microscopy.
We could make 3D-stacks and live-cell imaging movies of cells and neurons benefiting form the ~120 nm lateral resolution. See the how this compares to diffraction-limited imaging with this example from our samples: