New paper out: slow axonal transport of actin via hotspots and trails

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.

Details of hotspots seen by STORM
Quantification of hotspots diameter from STORM images

MiFoBio 2018: the best microscopy workshop!

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

photo: @HenriquesLab
COS cell labeled for actin and microtubules, imaged using Gataca System’s LiveSR spinning disk microscope
COS cell labeled for actin and microtubules, imaged using Olympus’ SpinSR10 spinning disk microscope

Brève Science & Vie

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.

New preprint: Get the best 3D localization microscopy with DAISY

We have a new preprint out! It’s a collaboration with the group of Sandrine Lévêque-Fort at ISMO (Orsay, France) based on the PhD work of Clément Cabriel. They previously used supercritical-angle fluorescence to measure the height of fluorophores at the proximity of the coverslip. This technique, called Direct Optical Nanoscopy with Axially Localized Detection (DONALD), could bring the resolution down to 15 nm for 3D localization microscopy. Now they have combined the SAF-based method with cylindrical lens astigmatism to obtain a robust and precise 3D localization of fluorophores over ~1.5 µm above the coverslip, retaining the key advantafges of DONALD: drift-free, tilt-insensitive and achromatic. The new technique, called Dual-view Astigmatic Imaging with SAF Yield (DAISY 😉), allowed to image in 3D the periodic scaffold of adducin and ß-spectrin along axons of cultured neurons, as you can see on the Figure below:
Cabriel_Preprint

Farewell to Nikki

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!