Our recent article on the ultrastructure of actin rings in the press

Two French scientific magazines have highlighted our recent article about the ultrastructure of axonal actin rings, both in their March issue: Science et Vie (bottom on the pic below) made a short story about it while Pour la Science (top) featured a PREM image of an axon as a beautiful double-page spread.

On the other side of the Atlantic, our work was featured in the March-April issue of the American Scientist magazine for their “Sightings” column. Happy to see our work getting attention in the press!

American Scientist "Sightings" Marc-April 2020

Visit to Turku and PhD defense in Helsinki

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!

New preprints: axonal clathrin transport packets

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!

clathrin along axons (Fig. from Ganguly et al., bioRxiv 2020)
Rendering of an axon segment (ß2-spectrin in green) containing clathrin packets (magenta)

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.

clathrin at presynapses (Fig. from Ganguly et al., bioRxiv 2020)
Check the rendering of clathrin packets (magenta) surrounding the presynaptic compartment (synapsin in green)

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

New preprint: immerse yourself in SMLM data with vLUME

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:

If you are interested, have a look at the movies highlighting the functions of vLUME and head over to GitHub to try the 1.0 version of the software.

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

New article out: Mapping the axon initial segment components by mass spectrometry

First work of 2020 work is out! A collaboration with Matt Rasband’s lab in Nature Communications. This is a significant paper for the axon initial segment field. Matt’s lab used BioID of key AIS proteins for mapping AIS components. Dozens of new candidates for future studies!

Check all these new AIS proteins!

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.

Mical3 is present along the AIS but does not associate with the periodic actin/spectrin scaffold.

Our paper is out! The ultrastructure of the axonal actin rings revealed

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.

It’s easier to go there to read it (and it’s open access!)

In this work that was made available as a preprint back 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.

Zooming from a cultured neuron to single ankyrins along the axon initial segment by correlative STORM/PREM

A press release from CNRS is available here in English and here in French for more details about this work. We are very happy to see it out!

Demoing the SoRa super-resolution spinning-disk microscope

For the last two weeks, we got to play with Nikon Instruments latest super-resolution spinning disk microscope that incorporates a Yokogawa SoRa head. It was installed in the INP NeuroCellular Imaging Service (NCIS) imaging facility.

The Nikon SoRa setup

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:

Comparison between raw spinning disk, raw SoRa, and deconvolved SoRa images of a COS cell labeled for actin, microtubules, clathrin and DNA.