Alex Ludwig

We have some news! We find that the post-synaptic Homer proteins coordinate YAP and Wnt signaling in epithelial cells, downstream of the Crumbs polarity complex. They do so by sequestering YAP and beta-catenin in biomolecular condensates, and by suppressing a FRYL/NDR complex. Check it out!

Intracellular mechanics and organelle mechanobiology Mechanobiology is an interdisciplinary field that emerges at the cross-section of biology, physics and engineering. It aims to understand how living cells, tissues and animals sense and respond to me…

Announcing a new @embo.org Workshop on "Intracellular mechanics and organelle mechanobiology" that we are organizing with Michael Krieg and Verena Ruprecht at @icfo.eu (Barcelona) on 16-20 February, 2026. Please, repost and spread the word! 🙏 #EMBOmechanobio

meetings.embo.org/event/26-org...

EMBO Cell Polarity and Membrane Dynamics workshop is off to a good start - as always :) #EMBO

A) Diagram of the RUSH system. The Halo-tagged cargo is retained in the ER by the binding of the Streptavidin binding peptide (SBP) to Streptavidin (StrepA), which is fused to the ER retention signal, KDEL. The cargo is synchronously released upon the addition of biotin, which outcompetes SBP for binding to Streptavidin.B) Diagram of the tagged cargo constructs used in this study. C) Steady state expression of UAS-SBP-Halo-Cadherin99c (magenta) under the control of traffic jam-Gal4, showing its localization to the apical microvilli. Phalloidin staining of F-actin (green) labels the apical microvilli in the follicle cells and the oocyte. Scale bar 10 µm. D) Steady state expression of UAS-SBP-SNAP-Ndg (magenta) under the control of traffic jam-Gal4, showing its localization to the basement membrane. Actin is shown in green. Scale bar 10 µm. E) En face view of SBP-SNAP-Ndg in the basement membrane. Scale bar 10 µm. F) Time course of SBP-Halo-Cadherin99C trafficking in fixed samples. G) 25 min after release from the ER, Cad99c (green) localizes to subapical puncta that are labeled by Rab11 (magenta). Scale bar 10 µm. In all figures with a cross-section of the follicle cells, apical is toward the top of the image and basal toward the bottom.

How are specific cargos targeted to apical & basolateral domains within #EpithelialCells? This study uses a novel #vesicle tracking software "MSP-tracker" to show that the secretory pathway in #Drosophila follicle cells is unexpectedly spatially organized @plosbiology.org 🧪 plos.io/3EfJsBp

Entzugserscheinungsangst :)

ARHGAP12 suppresses F-actin assembly to control epithelial tight junction mechanics and paracellular leak pathway permeability Tambrin et al. show that the Cdc42/Rac GAP ARHGAP12 promotes the flux of macromolecules across tight junctions by suppressing junctional actin assembly and tension via N-WASP and the Arp2/3 complex. T...

Our paper on the regulation of the tight junction leak pathway by Arhgap12/N-Wasp is out ! www.cell.com/cell-reports...

Why am I not surprised…

Science under siege: protecting scientific progress in turbulent times As Editors-in-Chief of The Company of Biologists' journals, we have been watching with growing concern the policy changes in the United States of America (USA) and the challenges that these are creati...

journals.biologists.com/jcs/article/...

Altogether we propose that the fusion of VACs with the AMIS provides an efficient mechanism for the rapid specification of apical domain identity. In addition, Pals1 and PatJ appear to be critical for VAC fusion at the AMIS, possibly due to their role in regulating the apical actin cytoskeleton.

Finally, we asked how VAC exocytosis at the AMIS is regulated and found that loss of the Crb complex proteins Pals1 or PatJ results in the intracellular accumulation of VACs and severe defects in lumen formation. Apical actin levels and the apical cell cortex were markedly altered in PatJ KO cells.

We further present evidence that VACs arise from the internalisation of microvilli-enriched membrane pits at the ECM facing side of cell doublets. How these membrane pits are internalised and how VACs are trafficked to and fuse with the AMIS is currently unclear.

We then analysed lumen initiation in MDCK 3D cultures. Using LM and EM we identified intracellular VACs and observed fusion events of VACs with the Apical Membrane Initiation Site (AMIS). Interestingly, VAC fusion at the AMIS was again coordinated with the formation of cell-cell junctions.

Interestingly, our time-resolved proteome revealed distinct recruitment profiles of Rho and Ras GTPases, tight junction membrane and scaffolding proteins, as well as apical proteins, providing new insight into the temporal execution of cell polarity development.

This set of experiments demonstrated that apical lumens are initiated by the exocytosis of large intracellular organelles at nascent cell-cell contact sites. Such organelles contain a pre-assembled microvilli-rich cortex and are known as Vacuolar Apical Compartments (VACs), or apicosomes.

To understand how apical lumen initiation and cell-cell junction assembly are coordinated, we initially analysed polarity development using the calcium switch assay, serial section TEM, and time-resolved proximity proteomics with our favourite enzyme APEX2. This is all done in MDCK cells.

Bulk exocytosis of large intracellular apical precursor organelles establishes apical domain identity during de novo lumen formation The creation of a microvilli-rich apical luminal domain is a key event in the development of epithelial tissues. De novo lumenogenesis, in which epithelial cells establish apical identity by directing...

We have some exciting news about how epithelial cells initiate an apical lumen de novo, and how this is coordinated with cell-cell junction formation. Check it out: www.biorxiv.org/content/10.1...

Another beautiful tight junction. This time with scale bar :)

Not bad for a conventionally fixed and dehydrated TEM sample. No HPF/FS. OTO method. Stains the kissing points quite nicely.

First official post! A new paper out about #cytokinesis in #epithelia

www.embopress.org/doi/full/10....

Explore our journey as we uncover how regulators of cell-cell and cell-matrix interactions modulate cytokinesis efficiency, while revealing new roles for the Dystrophin-Dystroglycan complex.

This is sabotage! And this may well be just the beginning.

You don’t have to be German to know what this stands for - it’s clear as mud - and it’s disgusting!

You don’t have to be German to know what this means - it’s clear as mud - and it’s disgusting

iAPEX: Improved APEX-based proximity labeling for subcellular proteomics using an enzymatic reaction cascade https://www.biorxiv.org/content/10.1101/2025.01.10.632381v1

Our #CryoET paper on ciliary rootlet ultrastructure from mouse retina is now out in @elife.bsky.social! Have a peek with this video or dive deeper at bit.ly/3ZJzhgc. Big thanks to @carter-lab.bsky.social and #teamtomo.

#CryoET #CryoEM #Cilia #Rootlet #Centriole #Research #Science

Beautiful! Great work

Mind blowing! Look at those nuclear pores.

Would love to be added here - thank you!

Still one of my favourite tomograms, recorded ages ago at NCMIR (UCSD). It shows interconnected networks of caveolae (labeled with a miniSOG probe) at the rear of RPE1 cells. Bummer we so far haven't been able to image such networks in larger cell volumes; it's a lot of membrane that's stored here.

Oh wtf

oh... what happened here? why overlapping holes? two grids on top of each other?