Biology subjects

Müller, D.

Publications and source records attributed to Müller, D..

8 recordsLinked to original sources

bioRxiv2026

ARF-1 Coordinates Cargo Sorting at FERARI Endosomal Recycling Hubs

Endosomal pathways are central to cellular organization, compartmentalization, and intercellular communication. Independent of the endocytic entry route, sorting endosomes function as critical junctions at which membrane proteins are sorted for recycling or degradation. The multicomponent tether FERARI orchestrates recycling by coordinating Rab GTPase activity with vesicle fusion and fission through a kiss-and-run mechanism. Here, we identify the small GTPase ARF-1 as an essential regulator of cargo loading at FERARI-dependent endosomal kiss-and-run (KAR) sites. Cycling of ARF-1 between its active and inactive states is required for efficient cargo capture into recycling vesicles. Our findings support a model in which cycling ARF-1 activity governs the temporal association of cargo with adaptor proteins and complexes, thereby controlling selective uptake into vesicles destined for the plasma membrane. These results uncover a previously unappreciated layer of regulation of endosomal recycling and highlight the interplay between ARF and Rab family GTPases in this process.

cell biology↗

bioRxiv2025

Kidney-specific Wdr72 deletion leads to incomplete distal renal tubular acidosis through impaired V-ATPase B1 subunit localization

BackgroundDistal renal tubular acidosis (dRTA) is a rare kidney disorder characterized by impaired urinary acidification due to defective proton secretion in type A intercalated cells of the collecting duct. Recently, pathogenic variants in the human gene encoding the WD Repeat Domain 72 protein (WDR72) have been reported in patients with dRTA, yet the physiological role of WDR72 in the kidney remains unknown. MethodsTo elucidate the renal function of Wdr72, we generated a kidney-specific knockout mouse model (Wdr72fl/fl;Pax8-Cre+) and assessed acid-base homeostasis under baseline, acute, and chronic acid loading. ResultsWdr72fl/fl;Pax8-Cre+ mice displayed persistently elevated urinary pH, reduced titratable acid and net acid excretion under basal and acid-loaded conditions, consistent with incomplete dRTA. While the systemic pH remained unchanged compared to controls under standard diet, chronic acid load led to mild hyperchloremic, hypokalemic metabolic acidosis. Notably, urinary NH excretion was increased upon acid loading accompanied by upregulation of key ammoniagenesis enzymes, which was detected even under basal conditions, consistent with a compensatory activation of proximal tubular acid excretion pathways. The total and membranous abundance of the V-ATPase B1 subunit decreased markedly within the kidney, despite unchanged transcript levels, suggesting a defect in V-ATPase trafficking or assembly. In addition, morphometric analyses revealed an increased proportion of type A intercalating cells that failed to expand upon acid loading, indicating defective adaptive plasticity. ConclusionsKidney-specific Wdr72 deletion impairs distal urinary acidification through reduced V-ATPase abundance and membranous targeting, altered intercalated cell morphology, and limited adaptive remodeling, resulting in incomplete dRTA. Upregulation of renal ammoniagenesis partially compensates the acidification defect. These findings highlight WDR72 as a key regulator of distal nephron acid-base homeostasis and offer mechanistic insight into WDR72-associated dRTA. Key PointsO_LIKidney-specific deletion of Wdr72 reduced Atp6v1b1 membranous localization in intercalated cells. C_LIO_LIKidney-specific Wdr72 knockout altered intercalated cell morphology, and limited their adaptive remodeling. C_LIO_LIThe lack of the renal Wdr72 resulted in incomplete dRTA, compensated partially by elevated ammoniagenesis. C_LI

molecular biology↗

bioRxiv2024

Ninjurin-1 mediated plasma membrane rupture is a two-step process requiring cell swelling

Ninjurin-1 (NINJ1) executes cell lysis by polymerizing into filaments, yet how these form membrane lesions is unknown. Integrating cell-based assays with molecular dynamics simulations, we demonstrate that NINJ1-driven membrane rupture starts with the lateral association of NINJ1 dimers into double filaments. Subsequently, swelling of necrotic cells increases plasma membrane tension, leading to separation of the filament interface and NINJ1 lesion opening. Inhibiting cell swelling prevents this increase in tension, blocking NINJ1-mediated plasma membrane rupture without disrupting NINJ1 oligomerization, implicating membrane tension as key for opening NINJ1 lesions. The NINJ1 homolog NINJ2 oligomerizes but fails to form membrane lesions during cell death due to the greater stability of its dimer. Finally, using atomic force microscopy of NINJ1-containing proteoliposomes, we show that NINJ1 forms large pores by stabilizing membrane edges. In summary, our findings support a model whereby membrane tension drives a zipper-like opening of NINJ1 double filaments, initiating necrotic cell lysis.

immunology↗

bioRxiv2024

Field conditions greatly modify a major growth-defense tradeoff in Arabidopsis thaliana

When plants defend themselves from pathogens, this often comes with a trade-off: the same genes that protect a plant from disease can also reduce its growth and fecundity in the absence of pathogens. One protein implicated in a major growth-defense trade-off in the plant Arabidopsis thaliana is ACCELERATED CELL DEATH 6 (ACD6), an ion channel that modulates salicylic acid (SA) synthesis to potentiate a wide range of defenses. Wild plant populations maintain significant functional variation in the ACD6 gene, with some alleles making the protein hyperactive. In the greenhouse, plants with hyperactive ACD6 alleles are resistant to diverse pathogens, yet are of smaller stature, their leaves senesce earlier, and they set fewer seeds. We hypothesized that such hyperactive alleles would not only affect the growth of microbial pathogens, but also more generally leaf microbiome assembly in the wild. To test this, we grew plants with hyperactive, standard, and defective ACD6 alleles in the same field-collected soil, both in climate-controlled conditions and outdoors. We surveyed visual phenotypes, gene expression, hormone levels, seed production, and the microbiome in each environment. To our surprise, we discovered that mature field plants, in stark contrast to greenhouse plants, were unaffected by their ACD6 genotype, suggesting that additional abiotic and/or microbial signals present outdoors - but not in the greenhouse - greatly modulate ACD6 activity.

plant biology↗

bioRxiv2023

Serotonin Reduces Belief Stickiness

Serotonin fosters cognitive flexibility, but how, exactly, remains unclear. We show that serotonin reduces belief stickiness: the tendency to get "stuck" in a belief about the state of the world despite incoming contradicting evidence. Participants performed a task assessing belief stickiness in a randomized, double-blind, placebo-controlled study using a single dose of the selective serotonin reuptake inhibitor (SSRI) escitalopram. In the escitalopram group, higher escitalopram plasma levels reduced belief stickiness more, resulting in better inference about the state of the world. Moreover, participants with sufficiently high escitalopram plasma levels had less belief stickiness, and therefore better state inference, than participants on placebo. Exaggerated belief stickiness is exemplified by obsessions: "sticky" thoughts that persist despite contradicting evidence. Indeed, participants with more obsessions had greater belief stickiness, and therefore worse state inference. The opposite relations of escitalopram and obsessions with belief stickiness may explain the therapeutic effect of SSRIs in obsessive-compulsive disorder.

neuroscience↗

bioRxiv2023

ER-dependent membrane repair of mycobacteria-induced vacuole damage

Several intracellular pathogens, such as Mycobacterium tuberculosis, damage endomembranes to access the cytosol and subvert innate immune responses. The host counteracts endomembrane damage by recruiting repair machineries that retain the pathogen inside the vacuole. Here, we show that the endoplasmic reticulum (ER)-Golgi protein oxysterol binding protein (OSBP) and its Dictyostelium discoideum homologue OSBP8 are recruited to the Mycobacterium-containing vacuole (MCV) after ESX-1-dependent membrane damage. Lack of OSBP8 causes a hyperaccumulation of phosphatidylinositol-4-phosphate (PI4P) on the MCV and decreased cell viability. OSBP8-depleted cells had reduced lysosomal and degradative capabilities of their vacuoles that favoured mycobacterial growth. In agreement with a function of OSBP8 in membrane repair, human macrophages infected with M. tuberculosis recruited OSBP in an ESX-1 dependent manner. These findings identified an ER-dependent repair mechanism for restoring MCVs in which OSBP8 functions to equilibrate PI4P levels on damaged membranes. ImportanceTuberculosis still remains a global burden and is one of the top infectious diseases from a single pathogen. Mycobacterium tuberculosis, the causative agent, has perfected many ways to replicate and persist within its host. While mycobacteria induce vacuole damage to evade the toxic environment and eventually escape into the cytosol, the host recruits repair machineries to restore the MCV membrane. However, how lipids are delivered for membrane repair is poorly understood. Using advanced fluorescence imaging and volumetric correlative approaches, we demonstrate that this involves the recruitment of the ER-Golgi lipid transfer protein OSBP8 in the D. discoideum/ M. marinum system. Strikingly, depletion of OSBP8 affects lysosomal function accelerating mycobacterial growth. This indicates that an ER-dependent repair pathway constitutes a host defence mechanism against intracellular pathogens such as M. tuberculosis.

cell biology↗

bioRxiv2021

Bloom syndrome helicase contributes to germ line development and longevity in zebrafish

RecQ helicases - also known as the guardians of the genome - play crucial roles in genome integrity maintenance through their involvement in various DNA metabolic pathways. Aside from being conserved from bacteria to vertebrates, their importance is also reflected in the fact that in humans impaired function of multiple RecQ helicase orthologs are known to cause severe sets of problems, including Bloom, Werner or Rothmund-Thomson syndromes. Our aim was to create and characterize a zebrafish (Danio rerio) disease model for Bloom syndrome, a recessive autosomal disorder. In humans, this syndrome is characterized by short stature, skin rashes, reduced fertility, increased risk of carcinogenesis and shortened life expectancy brought on by genomic instability. We show that zebrafish blm mutants recapitulate major hallmarks of the human disease, such as shortened lifespan and reduced fertility. Moreover, similarly to other factors involved in DNA repair, some functions of zebrafish Blm bear additional importance in germ line development, and consequently in sex differentiation. Unlike fanc genes and rad51, however, blm appears to effect its function independent of tp53. Therefore, our model will be a valuable tool for further understanding the developmental and molecular attributes of this rare disease, along with providing novel insights into the role of genome maintenance proteins in somatic DNA repair and fertility.

genetics↗

bioRxiv2018

Ykt6 membrane-to-cytosol cycling regulates exosomal Wnt secretion

Protein trafficking in the secretory pathway, for example the secretion of Wnt proteins, requires tight regulation. These ligands activate Wnt signaling pathways and are crucially involved in development and disease. Wnt is transported to the plasma membrane by its cargo receptor Evi, where Wnt/Evi complexes are endocytosed and sorted onto exosomes for long-range secretion. However, the trafficking steps within the endosomal compartment are not fully understood. The promiscuous SNARE Ykt6 folds into an auto-inhibiting conformation in the cytosol, but a portion associates with membranes by its farnesylated and palmitoylated C-terminus. Here, we demonstrate that membrane detachment of Ykt6 is essential for exosomal Wnt secretion. We identified conserved phosphorylation sites within the SNARE domain of Ykt6, which block Ykt6 cycling from the membrane to the cytosol. In Drosophila, Ykt6 RNAi-mediated block of Wg secretion is rescued by wildtype but not phosphomimicking Ykt6. We show that phosphomimicking Ykt6 accumulates at membranes, while wildtype Ykt6 regulates Wnt trafficking between the plasma membrane and multivesicular bodies in a dose-dependent manner. Taken together, we show that exosomal sorting of Wnts is fine-tuned by a regulatory switch in Ykt6 shifting it from a membrane-bound to cytosolic state at the level of endosomal maturation.

cell biology↗