Biology subjects

Laporte, M. H.

Publications and source records attributed to Laporte, M. H..

9 recordsLinked to original sources

bioRxiv2026

ALMS1 contributes to centriole proximal architecture and stability

Centrioles are highly organised microtubular scaffolds which grow and mature progressively during successive cell cycles. Their molecular organisation is extensively characterized, yet the contribution of several components to centriole assembly, maturation or stability is incompletely understood. Here, using ultrastructure expansion microscopy and transmission electron microscopy, we show that ALMS1, the protein mutated in Alstrom syndrome, is required for proper centriole architecture. In absence of ALMS1, RPE1 cells exhibit shorter centrioles with defects in the microtubular wall, including broken or missing triplets or open B/C tubules. These structural defects arise after procentriole assembly. We show that ALMS1 loss selectively reduces the proximal region proteins CCDC77 and CEP44, leaving intact central and distal ones. ALMS1 is further required for the recruitment of the proximal CEP135 cap and the clearance of the {gamma}-tubulin/GCP2 pool present at the procentriole base. Our findings thus identify ALMS1 as a key organiser of the centriole proximal domain and required for remodelling and stabilising the proximal end of centrioles during cell cycle progression.

cell biology↗

bioRxiv2026

Centrosome architecture and m6A-dependent gating of p53 surveillanceafter whole-genome doubling

Whole-genome doubling (WGD) generates a tetraploid state that challenges cellular homeostasis and is strongly selected against in TP53-proficient contexts. Although centrosome amplification serves as a structural correlate of genome doubling, how centrosomal features engage and sustain p53 surveillance remains incompletely understood. Here, we develop a genetically encoded MDM2-based fluorescent reporter to monitor Caspase-2 pathway activation in living cells after WGD. Combining pharmacological profiling and genome-wide CRISPR screening, we uncover a multi-layered regulation of p53 responses. We identify PLK1-dependent centriole maturation and subdistal appendage integrity as architectural determinants of PIDDosome-dependent Caspase-2 activation, independent of distal appendage assembly. We show that upon WGD, Caspase-2-mediated cleavage of MDM2 reshapes the p53-MDM2 regulatory loop, enabling sustained p53 signaling. This sustained output depends on the catalytic activity of METTL3 and associated m6A writer proteins. Together, these findings demonstrate that centrosome architecture and epitranscriptomic regulation cooperate to shape p53 surveillance after genome doubling. HighlightsO_LIWhole-genome doubling creates a surveillance state sensed by centrosome cluster architecture. C_LIO_LICaspase-2 activation converts the p53-MDM2 loop from negative to positive feedback. C_LIO_LIm6A methylation establishes competence of the p53 module for sustained output. C_LIO_LIA genetically encoded biosensor enables functional dissection of this circuit. C_LI

cell biology↗

bioRxiv2024

The A-C Linker controls centriole cohesion and duplication

Centrioles are evolutionarily conserved barrel-shaped organelles playing crucial roles in cell division and ciliogenesis. These functions are underpinned by specific structural sub-elements whose functions have been under investigation since many years. The A- C linker structure, connecting adjacent microtubule triplets in the proximal region, has remained unexplored due to its unknown composition. Here, using ultrastructure expansion microscopy, we characterized two recently identified A-C linker proteins, CCDC77 and WDR67, along with a newly discovered protein, MIIP. Our findings reveal that these proteins localize between microtubule triplets at the A-C linker, forming a complex. Depletion of A-C linker components disrupt microtubule triplet cohesion, leading to breakage at the proximal end. Co-removal of the A-C linker and the inner scaffold demonstrates their joint role in maintaining centriole architecture. Moreover, we uncover an unexpected function of the A-C linker in centriole duplication through torus regulation, underscoring the interplay between these protein modules.

cell biology↗

bioRxiv2022

Nanoscopy of organelles and tissues with iterative ultrastructure expansion microscopy (iU-ExM)

Expansion microscopy is an approach of super-resolution fluorescence microscopy that does not yet achieve the precision of nanoscopy techniques such as single-molecule light microscopy (SMLM). Here, we developed an iterative ultrastructure expansion microscopy approach (iU-ExM), which now matches the SMLM resolution as demonstrated using standard references such as the nuclear pores. Applicable to both cells and tissues, iU-ExM allows a broad research community to access high precision super-resolution microscopy.

cell biology↗

bioRxiv2022

Ultrastructure Expansion Microscopy reveals the nanoscale cellular architecture of budding and fission yeast

The budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe have served as invaluable model organisms to study various fundamental and highly conserved cellular processes. While super-resolution (SR) microscopy has in recent years paved the way to a better understanding of the spatial organization of molecules in cells, its wide use in yeast models has remained limited due to the specific know-how and specialized instrumentation required, contrasted with the relative ease of endogenous tagging and live cell fluorescence microscopy in these systems. To facilitate SR microscopy in yeasts, we have extended the ultrastructure expansion microscopy (U-ExM) method to both S. cerevisiae and S. pombe, enabling 4-fold isotropic expansion in both systems. We demonstrate here that U-ExM allows the nanoscale imaging of the microtubule cytoskeleton and its associated spindle pole body (SPB), notably unveiling a conserved Sfi1p/Cdc31p spatial organization on the appendage bridge structure. In S. pombe, we validate the method by quantifying the homeostatic regulation of nuclear pore complex (NPC) number through the cell cycle. Combined with pan-labelling (NHS ester), which provides a global cellular context, U-ExM unveils the subcellular organization of the eukaryote yeast models S. cerevisiae and S. pombe. This easy-to-implement imaging with conventional microscopes provides nanoscale resolution and adds a powerful new method to the already extensive yeast toolbox.

cell biology↗

bioRxiv2021

The ternary complex CEP90, FOPNL and OFD1 specifies the future location of centriolar distal appendages, and promotes their assembly

In metazoa, cilia assembly is a cellular process that starts with centriole to basal body maturation, migration to the cell surface and docking to the plasma membrane. Basal body docking involves the interaction of both the distal end of the basal body and the transition fibers / distal appendages, with the plasma membrane. Mutations in numerous genes involved in basal body docking and transition zone assembly are associated with the most severe ciliopathies, highlighting the importance of these events in cilium biogenesis. In this context, the ciliate Paramecium has been widely used as a model system to study basal body and cilia assembly. However, despite the apparent evolutionary conservation of cilia assembly events across phyla, whether the same molecular players are functionally conserved, is not fully known. Here, we demonstrated that CEP90, FOPNL and OFD1 form an evolutionary conserved complex that is crucial for ciliogenesis. Using ultrastructure expansion microscopy, we unveiled that these proteins localize at the distal end of both centrioles/basal bodies in Paramecium and mammalian cells. Moreover, we found that these proteins are recruited early after centriole duplication on the external surface of the procentriole and define the future location of the distal appendages. Functional analysis performed both in Paramecium and mammalian cells demonstrate the requirement of this complex for distal appendage assembly and basal body docking. Finally, we show that mammals require another component, Moonraker (MNR), to recruit OFD1, FOPNL, and CEP90, which will then recruits the distal appendage protein CEP83. Altogether, we propose that this ternary complex is required to determine the future position of distal appendages.

cell biology↗

bioRxiv2020

Paradoxical neuronal hyperexcitability in a mouse model of mitochondrial pyruvate import deficiency

Neuronal excitation imposes a high demand of ATP in neurons. Most of the ATP derives primarily from pyruvate-mediated oxidative phosphorylation, a process that relies on import of pyruvate into mitochondria occuring exclusively via the mitochondrial pyruvate carrier (MPC). To investigate whether deficient oxidative phosphorylation impacts neuron excitability, we generated a mouse strain carrying a conditional deletion of MPC1, an essential subunit of the mitochondrial pyruvate carrier, specifically in adult glutamatergic neurons. We found that, despite decreased levels of oxidative phosphorylation in these excitatory neurons, mice were normal at rest. Paradoxically, in response to mild inhibition of GABA mediated synaptic activity, they rapidly developed severe seizures and died, whereas under similar conditions the behaviour of control mice remained unchanged. We show that neurons with a deficient MPC are intrinsically hyperexcitable as a consequence of impaired calcium homeostasis, which reduces M-type potassium channel activity. Provision of ketone bodies restores energy status, calcium homeostasis and M-channel activity and attenuates seizures in animals fed a ketogenic diet. Our results provide an explanation for the paradoxical seizures that frequently accompany a large number of neuropathologies, including cerebral ischemia and diverse mitochondriopathies, in which neurons experience an energy deficit. One Sentence SummaryDecreased OXPHOS and Ca2+-mediated neuronal hyperexcitability lead to seizure in a mouse model of mitochondrial pyruvate import deficiency.

neuroscience↗

bioRxiv2020

ALG-2 interacting protein-X (Alix) is required for activity-dependent bulk endocytosis at brain synapses

In chemical synapses undergoing high frequency stimulation, vesicle components can be retrieved from the plasma membrane via a clathrin-independent process called activity dependent bulk endocytosis (ADBE). Alix (ALG-2 interacting protein X)/ PDCD6IP) is an adaptor protein binding to ESCRT and endophilin-A proteins which is required for clathrin-independent endocytosis in fibroblasts. Alix is expressed in neurons and concentrates at synapses during epileptic seizures. Here, we used cultured neurons to show that Alix is recruited to presynapses where it interacts with, and concentrates endophilin-A during conditions triggering ADBE. Using Alix knockout (ko) neurons we showed that this recruitment, which requires interaction with the calcium-binding protein ALG-2, is necessary for ABDE. We also found that presynaptic compartments of Alix ko hippocampi display subtle morphological defects compatible with flawed synaptic activity and plasticity detected electrophysiologically. Furthermore, mice lacking Alix in the forebrain undergo less seizures during kainate-induced status epilepticus and reduced propagation of the epileptiform activity. These results thus show that impairment of ADBE due to the lack of neuronal Alix alters synaptic recovery during physiological or pathological repeated stimulations.

neuroscience↗

bioRxiv2020

The inner scaffold protects from centriole fracture

Centrioles are characterized by a nine-fold arrangement of long-lived microtubule triplets that are held together by an inner protein scaffold. These structurally robust organelles experience strenuous cellular processes such as cell division or ciliary beating while performing their function. However, the molecular mechanisms underlying the stability of microtubule triplets, as well as centriole architectural integrity remain poorly understood. Here, using ultrastructure expansion microscopy (U-ExM) for nanoscale protein mapping, we reveal that POC16 and its human homolog WDR90 are components of the centriolar microtubule wall along the central core region of the centriole. We further found that WDR90 is an evolutionary microtubule associated protein with a predicted structurally homology with the ciliary inner junction protein FAP20. Finally, we demonstrate that WDR90 depletion impairs the localization of inner scaffold components, leading to centriole structural abnormalities in both human and Chlamydomonas cells. Altogether, this work highlights that POC16/WDR90 is a crucial evolutionary conserved molecular player participating in centriole architecture integrity.

cell biology↗