Sophie G Martin

Working model for the major pathways of plasma membrane deposition and septum formation during cytokinesis. The septum is illustrated asymmetrically intentionally. The top half septum shows septum formation and digestion of the primary septum; the bottom half shows septum formation. (1) F-BAR protein Cdc15 (and others) anchor the contractile ring to the plasma membrane, which recruits the β(1,3)-glucan synthase Bgs1 and its adaptor Sbg1 for primary septum formation. (2) Association of the F-BAR protein Rga7 and coiled-coil protein Rng10 with the Munc13/UNC-13 protein Ync13 recruits the TRAPP-II complex along the cleavage furrow, which tethers vesicles and primes the SM protein Sec1 and its binding partner Mso1 for the SNARE complex assembly to trigger vesicle fusion with the plasma membrane. This pathway maintains normal levels and distribution of gluacan synthases Bgs4/Smi1 and Ags1 for secondary septum formation. (3) The anillin Mid2 and septin rings restrict most of the exocyst complex to the rim of cleavage furrow to tether secretory vesicles loaded with the glucanases Eng1 and Agn1 and other cargos for digestion of primary septum to trigger daughter-cell separation.

How is #cytokinesis coordinated to ensure successful #CellDivision? Jian-Qiu Wu @sophiemartinlab.bsky.social &co show that the Ync13-Rga7-Rng10 module coordinates selective tethering & fusion of vesicles containing glucan synthases at the division site @plosbiology.org 🧪 plos.io/43zJ35Z

It is with great sadness that the University shares the news of the death of Professor Sir John Gurdon, founder of the @gurdoninstitute.bsky.social

Read our tribute to the visionary Nobel Laureate and watch an interview from 2012, just after he won: https://bit.ly/4mM8o3r

@biology-unige.bsky.social

Amazingly, her work also led to Sms1, which @borissieber.bsky.social had identified by biochemical means and found to be the long sought-after MAPK scaffold.

Very satisfying to come to the same gene through completely different routes! 😀

bsky.app/profile/bori...

Starting from cells strongly impaired for cell fusion (lacking the gene prm1), she evolved enhanced cell fusion capacity, which she showed occurs through both changes in regulatory pathways that lead to increasing fusion attempts, and also through emergence of a latent pathway.

Super happy to see also this story out! 👇

7 years of amazing perseverance from @gaowen.bsky.social, who not only performed experimental evolution showing tradeoff between sexual and asexual reproduction, but also identified all key transcription and genome changes.

www.biorxiv.org/content/10.1...

Thanks! We know your papers well! 😀

Super excited that this story by @borissieber.bsky.social is now on BioRxiv!

For decades, we thought there was no MAPK scaffold for the ERK-like cascade that promotes sexual reproduction in fission yeast ... until Boris found it !

See the thread 👇 and enjoy the paper!

doi.org/10.1101/2025...

Our department of Plant Molecular Biology at the University of Lausanne @unil.bsky.social is recruiting a Tenure-Track Assistant Professor in the field of Plant-Organism Interactions 🌱🐛🦠🍄! Application before November 30, 2025. See the official job ad for more details: tinyurl.com/mtxdcz6p

Hello microscopy and imaging experts and enthusiasts!
We are looking for a staff scientist to join us here in Geneva to work on microscopy and image analysis projects! See the link for the job announcement (in French and in English).

Please apply and/or repost!

jobs.unige.ch/www/wd_porta...

Come and Join our Dpt in Beautiful #Geneva !

We are looking for a #Microscopy & #Image #Analysis expert to help all of us at the Dpt.

Localization of WDS proteins and fimbrin in three fungal species.

How do cells switch on the actin assembly at endocytic sites? How can this on-switch evolve? Check out our new preprint!
www.biorxiv.org/content/10.1...

Congrats Monica! This is amazing 🤩

🚨 New preprint!
Using U-ExM + in situ cryo-ET, we show how C2CD3 builds an in-to-out radial architecture connecting the distal centriole lumen to its appendages. Great collab with @cellarchlab.com @chgenoud.bsky.social @stearnslab.bsky.social 🙌. #TeamTomo #UExM
www.biorxiv.org/content/10.1...

Great job opportunity at The Center for Integrative Genomics, Lausanne University, Switzerland unil.ch/cig/en/home....
For a tenure-track Assistant Professor position. More details for how to apply are here nature.com/naturecareer...

New tenure track assistant professor position in molecular microbiology in our department @dmf-unil.bsky.social @unil.bsky.social! We are casting a wide net for an experimental molecular microbiologist. Apply here: wwwfbm.unil.ch/releve/appli...

Beautiful images 🤩

Schematics of the actin fusion focus

New lab preprint! High resolution mapping of the actin fusion focus reveals myosin V-dependent transport of formin for actin aster compaction.

A very cool work led by @valthomas.bsky.social and nice collaboration with Andrea Picco and @kaksonen.bsky.social!

www.biorxiv.org/content/10.1...

Congrats Caren! Back to the source!

The surprise is that, over the same fold-change, cellular dimensions vary linearly with Cdc42 protein levels. So polarized growth has a linear relationship with Cdc42 levels.

➡️ Open question: How does this match with all the positive and negative feedback regulation that control Cdc42 activity?

To test the importance of protein levels, we created an allelic series, exploring a 5-fold range in Cdc42 expression levels.

We found that Cdc42 levels exhibit a switch-like transition for function during sexual reproduction, going from sterile to fully fertile cells within a 2-fold change.

With several variants of cdc42 exhibiting cell fusion defects, including a widely used tagged allele (cdc42-mCherrySW) and mutants in cdc42 introns, we realized what they had in common: low levels of Cdc42 protein expression.

We found that Cdc42 GTPase localizes to the site of cell-cell fusion in S. pombe cells (arrow in image) and plays important roles in the late stages of polarized secretion to promote local cell wall digestion.

High levels of Cdc42 GTPase underlie an all-or-none decision to fuse Cdc42 is a Rho-family GTPase conserved across eukaryotes, where it plays essential roles in cell polarization. In single-celled yeast systems, Cdc42 is a key driver of symmetry breaking and polarized ...

The lab is on a roll. 2nd preprint in as many weeks!

High levels of Cdc42 GTPase underlie an all-or-none decision to fuse.

Great team effort led by PhD students @sajjitasaha.bsky.social and @aiswaryasajeevan.bsky.social

www.biorxiv.org/content/10.1...

@biology-unige.bsky.social

Thanks Omaya!

Does this mechanism ring a bell?
It is conceptually remarkably similar to how spindle poles form. It seems like the same principles apply to form cytoskeletal asters, whether based on actin or microtubules.

#actin #microtubules #cytoskeleton

Transport of formin by myosin V

Thus, by transporting Fus1 along actin filaments nucleated by other Fus1 dimers, the formin-myoxin V association underlies positive feedback convergence of actin filaments in the focus.

… and we find that the formin Fus1 is a myosin V cargo!

The movie shows coincident formin Fus1 (green) and myosin V Myo52 (magenta) signals converging together.

Spatiotemporal map of the actin fusion focus

The cool finding is that the myosin V Myo52 (red), which transports secretory vesicles (purple) onto the fusion focus, dissociates from the pool of vesicles and joins the formin Fus1 (green) that assembles the focus. The two proteins physically associate…

Spatiotemporal map of the actin fusion focus

We developed a three-color live fluorescence-imaging method that allows mapping the position of protein pools with a precision of 8 nm.

Applying it to the actin fusion focus, an #actin aster that underlies yeast #cell_fusion, we show stereotypical order and compaction of the structure.