Biology subjects

Nicolle, O.

Publications and source records attributed to Nicolle, O..

11 recordsLinked to original sources

bioRxiv2026

GCK-4 regulates apical actin organization and lumen formation in the C. elegans intestine

Epithelial tubes are an essential component of many organ systems. The formation of their lumens depends on the close coordination of epithelial polarity, the apical actin cytoskeleton, and apical junctions, yet the mechanisms that organize the apical cytoskeleton and junctions downstream of polarity remain poorly understood. Here, we identify the Ste20 family kinase GCK-4, the single C. elegans ortholog of the mammalian kinases LOK and SLK, as a critical regulator of intestinal lumen formation. GCK-4 localizes to the apical membrane during early lumen formation and to microvillar tips as these structures develop. Its loss results in a lethal cystic lumen phenotype, without disrupting the establishment of epithelial polarity, and in occasional failure to maintain attachment between the pharynx and intestine. Lumens in gck-4 mutant animals show irregular junction patterning, severely impaired apical accumulation of both actin and the membrane-actin linker Ezrin/Radixin/Moesin protein ERM-1, and microvilli atrophy. In Drosophila and mammalian cells, the GCK-4 orthologs are thought to organize the apical actin network largely through phosphorylation of ERM proteins. In contrast, ERM-1 phosphorylation is only partially reduced in gck-4 mutants and is not abolished, indicating that GCK-4 acts through additional targets and is not the principal ERM-1 kinase in the intestine. Together, these findings identify GCK-4 as a key regulator of apical actin and junction organization during lumen formation, and demonstrate that Ste20 kinases can control apical cytoskeletal architecture at least partially independently of ERM phosphorylation.

developmental biology↗

bioRxiv2024

Dynamics of gut colonization by commensal and pathogenic bacteria that adhere to the intestinal epithelium

Maintaining a healthy gut microbiome plays a critical role in avoiding gut-related pathologies. Bacterial adherence to the intestinal epithelium plays a vital role in niche establishment in the gut, as in vitro experiments and mathematical modeling suggest that adherence provides a strong competitive advantage over free-floating planktonic microbes. Currently, we lack the ability to study gut microbiome adherence in an in vivo model system. Through sampling natural populations of Caenorhabditis, we discovered three bacterial species that adhere to the intestinal epithelium of several wild Caenorhabditis isolates. When transferred to C. elegans, all three bacterial species colonized the entire anterior to posterior length of the intestine lumen. We isolated these bacterial species via in vitro growth or selective enrichment in the nematode gut and identified them as Lelliottia jeotgali, Candidatus Lumenectis limosiae, and Candidatus Enterosymbion pterelaium, the latter two representing new species. Adherent Ca. L. limosiae negatively affects host fitness, while Lelliottia jeotgali and Ca. E. pterelaium exhibited a neutral effect in our assays. We demonstrated that two of these species can actively proliferate in the intestine throughout the host lifespan, with Lelliottia jeotgali colonizing throughout the lumen simultaneously and Candidatus Lumenectis limosiae showing anterior-to-posterior directionality. In competition assays, animals pre-colonized with L. jeotgali significantly reduced colonization by pathogenic Ca. L. limosiae, but this effect was not seen when animals were colonized by both bacteria simultaneously. Strikingly, regardless of the colonization paradigm, populations exposed to both bacteria showed a near-identical mitigation of the pathogenic effects of Ca. L. limosiae. Altogether, these strains illustrate the capacity of microbiome bacteria to adhere, replicate, and establish a niche across the entire intestinal lumen in C. elegans and they present an opportunity to study bacterial adherence in the context of a whole, intact and transparent animal.

microbiology↗

bioRxiv2023

SIN-3 transcriptional coregulator maintains mitochondrial hormesis and polyamine flux

Mitochondrial function relies on the coordinated transcription of mitochondrial and nuclear genomes to assemble respiratory chain complexes. Across species, the SIN3 coregulator influences mitochondrial functions, but how its loss impacts mitochondrial homeostasis and metabolism in the context of a whole organism is unknown. Exploring this link is important because SIN3 haploinsufficiency causes intellectual disability/autism syndromes and SIN3 plays an important role in tumor biology. Here we show that loss of C. elegans SIN-3 results in transcriptional deregulation of mitochondrial- and nuclear encoded mitochondrial genes, potentially leading to mito-nuclear imbalance. Consistent with impaired mitochondrial function, sin-3 mutants show extensive mitochondrial fragmentation by transmission electron microscopy (TEM) and in vivo imaging, and altered oxygen consumption. Metabolomic analysis of sin-3 mutant animals identifies a signature of mitochondria stress, and deregulation of methionine flux resulting in decreased S-adenosyl methionine (SAM), and increased polyamine levels. Our results identify SIN3 as a key regulator of mitochondrial dynamics and metabolic flux, with important implications for human pathologies.

developmental biology↗

bioRxiv2023

The clathrin adaptor AP-1B independently controls proliferation and differentiation in the mammalian intestine.

Maintenance of the polarity of the epithelial cells facing the lumen of the small intestine is crucial to ensure the vectorial absorption of nutrients as well as the integrity of the apical brush border and the intestinal barrier. Polarized vesicular trafficking plays a key role in this process, and defective transport due to mutations in apical trafficking-related genes has been shown to affect nutrient absorption. Interestingly, it has been demonstrated that downregulation of the polarized sorting clathrin adaptor AP-1B led to both epithelial polarity and proliferation defects in the mouse intestine. This enlightened a new function of polarized trafficking in the gut epithelium and a novel link between trafficking, polarity, and proliferation. Here, using CRISPR-Cas9-mediated mutation of the AP-1B coding gene Ap1m2 in mouse intestinal organoids, we uncovered a novel proliferation pathway controlled by AP-1B. We showed that the polarity defects induced by Ap1m2 mutations led to a defective apical targeting of both Rab11+ apical recycling endosomes and of the polarity determinant Cdc42. Moreover, we showed that these polarity defects were accompanied by an induction of YAP and EGFR/mTOR-dependent proliferation pathways. Finally, we showed that AP-1B additionally controlled a proliferation-independent differentiation pathway towards the secretory lineage. Overall, our results highlighted the pleiotropic roles played by AP-1B in the homeostasis of the gut epithelium.

cell biology↗

bioRxiv2022

V0-ATPase downregulation induces MVID-like brush border defects independently of apical trafficking in the mammalian intestine

SummaryIntestinal microvillus atrophy is a major cause of enteropathies such as idiopathic or congenital diarrhea that are often associated with severe morbidity. It can be caused by genetic disorders, inflammatory diseases, toxins or pathogens. In particular, Microvillus inclusion disease (MVID) is characterized by a chronic intractable diarrhea and a severe microvillus atrophy. It is triggered by mutations in MYO5B, STX3, MUNC18.2 or UNC45A which alter epithelial polarity by affecting apical trafficking in intestinal epithelial cells. Furthermore, we recently established that the depletion of the V0 sector of the V-ATPase complex induces an MVID-like phenotype in C. elegans. In this study we investigated the function of the V0-ATPase complex in mouse intestinal organoids. We found that its depletion also triggers a very severe microvillus atrophy in this model. Furthermore, we established that the polarity of intestinal cells is affected in a patient carrying mutations in TCIRG1 which encodes a V0-ATPase subunit. However, V0- ATPase depletion does not recapitulate other MVID-specific phenotypes such as subapical vesicle accumulation and Rab11+ endosomes mislocalization. Finally, we found that the apical localization of the V0-ATPase is disrupted in MVID patients. Altogether these results suggest a role for the V0-ATPase in microvillus atrophy which might be independent from apical trafficking.

cell biology↗

bioRxiv2022

PAR-4/LKB1 regulates intestinal cell number by restricting endoderm specification to the E lineage

The master kinase PAR-4/LKB1 appears as a major regulator of intestinal physiology. It is in particular mutated in the Peutz-Jeghers syndrome, an inherited disorder in which patients develop benign intestine polyps. Moreover, ectopic activation of PAR-4/LKB1 is sufficient to induce the polarized accumulation of apical and basolateral surface proteins and the formation of apical microvilli-like structures in intestinal epithelial cancer cell lines. In C. elegans, PAR-4 was shown to be required for the differentiation of intestinal cells. Here, we further examine the role of PAR-4 during intestinal development. We find that it is not required for the establishment of enterocyte polarity and plays only a minor role in brush border formation. By contrast, par-4 mutants display severe deformations of the intestinal lumen as well as supernumerary intestinal cells, thereby revealing a novel function of PAR-4 in preventing intestinal hyperplasia. Importantly, we find that the ability of PAR-4 to control intestinal cell number does not involve the regulation of cell proliferation but is rather due to its ability to restrict the expression of intestinal cell fate factors to the E blastomere lineage. We therefore propose that PAR-4 is required to regulate C. elegans intestine specification.

developmental biology↗

bioRxiv2021

Myosin-1b interacts with UNC45A and controls intestinal epithelial morphogenesis

Vesicle trafficking and the establishment of apico-basal polarity are essential processes in epithelium morphogenesis. Myosin-1b, an actin-motor able to bind membranes, regulates membrane shaping and vesicle trafficking. Here, we investigate Myosin-1b function in gut morphogenesis and congenital disorders using cell line and zebrafish larvae as well as patient biopsies. In a 3D Caco-2 cyst model, lumen formation is impaired in absence of Myosin-1b. In zebrafish, both Morpholino knock-down and genetic mutation of myo1b result in intestinal bulb epithelium folding defects associated with vesicle accumulation, reminiscent of a villous atrophy phenotype. We show that Myosin-1b interacts with the chaperone UNC45A, genetic deletion of which also results in gut folding defects in zebrafish. Loss of function mutations in UNC45A have been reported in complex hereditary syndromes, notably exhibiting intestinal disorders associated with villous atrophy. In UNC45A-depleted cells and in patient biopsies, Myosin-1b protein level is strikingly decreased. The appearance of Myosin-1b aggregates upon proteasome inhibition in cells points at a degradation mechanism of misfolded Myosin-1b in the absence of its chaperone. In conclusion, Myosin-1b plays an unexpected role in the development of the intestinal epithelium folds or villi downstream UNC45A, establishing its role in the gut defects reported in UNC45A patients. Summary statementMyosin-1b is important for intestinal epithelium folding during zebrafish development and participates in the villous atrophy clinical manifestation downstream UNC45A loss of function.

developmental biology↗

bioRxiv2021

High resolution dynamic mapping of the C. elegans intestinal brush border

The intestinal brush border is made of an array of microvilli that increases the membrane surface area for nutrient processing, absorption, and host defence. Studies on mammalian cultured epithelial cells uncovered some of the molecular players and physical constrains required to establish this apical specialized membrane. However, the building and maintenance of a brush border in vivo has not been investigated in detail yet. Here, we combined super-resolution imaging, transmission electron microscopy and genome editing in the developing nematode C. elegans to build a high-resolution and dynamic localization map of known and new markers of the brush border. Notably, we show that microvilli components are dynamically enriched at the apical membrane during microvilli outgrowth and maturation but become highly stable once microvilli are built. This new mapping tool will be instrumental to understand the molecular processes of microvilli growth and maintenance in vivo as well as the effect of genetic perturbations, notably in the context of disorders affecting brush border integrity.

developmental biology↗

bioRxiv2020

In vivo control of the ezrin/radixin/moesin protein ERM-1 in C. elegans

ERM proteins are conserved regulators of cortical membrane specialization, that function as membrane-actin linkers and molecular hubs. Activity of ERM proteins requires a conformational switch from an inactive cytoplasmic form into an active membrane- and actin-bound form, which is thought to be mediated by sequential PIP2-binding and phosphorylation of a conserved C-terminal threonine residue. Here, we use the single C. elegans ERM ortholog, ERM-1, to study the contribution of these regulatory events to ERM activity and tissue formation in vivo. Using CRISPR/Cas9-generated erm-1 mutant alleles we demonstrate that PIP2-binding is critically required for ERM-1 function. In contrast, dynamic regulation of C-terminal T544 phosphorylation is not essential but modulates ERM-1 apical localization and dynamics in a tissue-specific manner, to control cortical actin organization and drive lumen formation in epithelial tubes. Our work highlights the dynamic nature of ERM protein regulation during tissue morphogenesis and the importance of C-terminal phosphorylation in fine-tuning ERM activity in a tissue-specific context.

cell biology↗

bioRxiv2018

The loss of V0-ATPase induces Microvillus inclusion-like disease in C. elegans

Intestine function relies on the strong polarity of intestinal epithelial cells and the array of microvilli forming a brush border at their luminal pole. Combining genetic RNAi screen and in vivo super-resolution imaging in the C. elegans intestine, we uncovered that the V0 sector of the V-ATPase (V0-ATPase) controls a late apical trafficking step, involving RAB-11 endosomes and the SNARE SNAP-29, necessary to maintain the polarized localization of both apical polarity modules and brush border proteins. We show that the V0-ATPase pathway also genetically interacts with glycosphingolipids in enterocyte polarity maintenance. Finally, we demonstrate that depletion of the V0-ATPase fully recapitulates the severe structural, polarity and trafficking defects observed in enterocytes from patients with Microvillus inclusion disease (MVID) and used this new in vivo MVID model to follow the dynamics of microvillus inclusions. Hence, we describe a new function for the V0-ATPase in apical trafficking and epithelial polarity maintenance and the promising use of C. elegans intestine as an in vivo model to better understand the molecular mechanisms of rare genetic enteropathies.\n\nSummary statementV0-ATPase controls a late apical trafficking step involved in the maintenance of the apical absorptive intestinal membrane and its depletion phenocopies the trafficking and structural defects of MVID in C. elegans.

cell biology↗

bioRxiv2017

Coordinated morphogenesis through tension-induced planar polarity

Tissues from different developmental origins must interact to achieve coordinated morphogenesis at the level of a whole organism. C. elegans embryonic elongation is controlled by actomyosin dynamics which trigger cell shape changes in the epidermis and by muscle contractions, but how the two processes are coordinated is not known. We found that a tissue-wide tension generated by muscle contractions and relayed by tendon-like hemidesmosomes in the dorso-ventral epidermis is required to establish a planar polarity of the apical PAR module in the lateral epidermis. This planar polarized PAR module then controls actin planar organization, thus determining the orientation of cell shape changes and the elongation axis of the whole embryo. This trans-tissular mechanotransduction pathway thus contributes to coordinate the morphogenesis of three embryonic tissues.

developmental biology↗