Biology subjects

Verlhac, M.-H.

Publications and source records attributed to Verlhac, M.-H..

12 recordsLinked to original sources

bioRxiv2026

Elevated cortical tension triggers precocious ectopic polarization in mammalian oocytes, associated with lower developmental potential.

Oocytes from many organisms polarize early during development, unlike mammalian oocytes. The significance of maintaining this homogeneous state in mammals remains unclear. We show that elevated cortical tension, via increased actomyosin contractility or disrupted cortical architecture, induces precocious cortical polarization mid-meiosis I, with an ectopic actomyosin-rich domain opposite the future division site. This polarization generates directional cytoplasmic flows that displace organelles and the spindle, accelerating its migration and disrupting its orientation. A hydrodynamic model coupling the polarized cortex to a viscous cytoplasm accounts for these rearrangements. Ectopic polarization persists in meiosis II and is associated with mislocalization of fertilization factors, increased fertilization rates and polyspermy, and reduced early embryonic development. A similar morphological signature arises spontaneously in subsets of mouse and human oocytes. These results reveal precocious cortical polarization as a previously unrecognized, mechanically accessible state largely absent from mammalian oocytes, which may contribute to variability in oocyte quality.

cell biology↗

bioRxiv2026

The post-transcriptional RNA splicing landscape driving oocyte division

During growth in ovaries, mammalian oocytes accumulate maternal transcripts, proteins, and metabolites that support meiotic divisions and embryogenesis. As oocytes become fully grown, RNA Polymerase II is degraded and transcription is effectively silenced. However, RNA splicing appears to be required for oocyte division, a requirement which remains poorly characterized. Here, we define this post-transcriptional RNA splicing landscape of fully grown mouse oocytes and develop a computational resource that identifies post-transcriptional splicing events, signatures, sequence features, and protein binding motifs responsive to splicing perturbation. We show that, unlike transcription, RNA splicing in fully grown oocytes is essential for meiotic progression. Applying our resource across perturbations, we identify hundreds of genes whose proper splicing is required for oocyte division and reveal that distinct perturbations converge on overlapping regulatory programs controlling cytoskeletal organization and cell cycle progression that drive oocyte division. We experimentally validate selected resource-derived predictions using chemical and protein-based splicing perturbations. These findings demonstrate that extensive RNA processing persists after transcription has ceased and position post-transcriptional splicing as a fundamental regulator of mammalian oocyte development.

developmental biology↗

bioRxiv2025

A novel RNP compartment boosts translation in growing mouse oocytes to avoid cytoplasm dilution

Mammalian oocytes undergo a long growth phase in the ovary, during which transcriptional levels gradually decrease. Growing oocytes must therefore accumulate maternal stores and regulate their translation to achieve successful divisions and early embryo development. Using immunofluorescence, mass spectrometry and electron microscopy, we identified a novel and transient compartment, the Zollo Body, in late growing mouse oocytes, constituted of RNPs and organelles. Morphologically, this structure resembles the Balbiani body found in most vertebrate species but it stains positively for nascent translation and active phospho-mTOR. RNAseq analysis and dry mass measurements of growing oocytes with or without this compartment further support its key role in boosting translation, allowing growing oocytes to avoid cytoplasmic dilution despite their rapid size increase, ultimately ensuring their developmental potential.

cell biology↗

bioRxiv2025

Atomic Force Microscopy reveals differences in mechanical properties linked to cortical structure in mouse and human oocytes

Cell mechanical properties regulate biological processes such as oocyte development. Cortical tension is regulated via actomyosin cortex remodeling to ensure optimal oocyte quality. However, the evolution of other mechanical parameters and their relationship with cortex structure remain poorly understood in mammalian oocytes. In this work, we propose a methodology combining multiple mechanical parameters measured through Atomic Force Microscopy to investigate the relationship between oocyte mechanical properties and cortex organization. By studying mouse oocytes at various stages of development, along with engineered ones with specific cortex organization, we demonstrate that a thin actin cortex corresponds to stiff oocytes while a thick one is associated with softer oocytes. We further reveal that maternal age, a critical factor for fertility, affects mouse oocytes mechanics correlating with alterations in their cortex structure. Finally, we show that the evolution of mechanical properties differs between human and mouse oocyte development, highlighting species-specific differences in cortex organization.

biophysics↗

bioRxiv2025

Non-invasive characterization of oocyte deformability in micro-constrictions

Oocytes naturally present mechanical defects that hinder their development after fertilization. Thus, in the context of assisted reproduction, oocyte selection based on their mechanical properties has great potential to improve the quality of the resulting embryos and the success rate of these procedures. However, the use of mechanical properties as a quantifiable selective criterion requires robust and non-destructive measurement tools. This study developed a constriction-based microfluidic device that monitors the deformation of mouse oocytes under controlled pressure. The device can distinguish mechanically aberrant oocyte groups from healthy control ones. Based on a mathematical model, we propose that deformability measurements infer both oocyte tension and elasticity, elasticity being the most discriminating factor in our geometry. Despite force transmission during oocyte deformation, no long-term damage was observed. This non-invasive characterization of mouse oocyte deformability in micro-constrictions allows for a significant advance in assessing the mechanical properties of mammalian oocytes and has potential application as a quantifiable selective criterion in medically assisted reproduction. TeaserA measurement method for translating advances in oocyte mechanics into selection criteria for improving medically assisted reproduction.

developmental biology↗

bioRxiv2022

The filipodia-like protrusions of adjacent somatic cells shape the developmental potential of mouse oocytes

The oocyte must grow and mature before fertilization, thanks to a close dialogue with the somatic cells which surround it. Part of this communication is through filopodialike protrusions, called transzonal projections (TZPs), sent by the somatic cells to the oocyte membrane. To investigate the contribution of TZPs to oocyte quality, we impaired their structure by generating a full knockout mouse of the TZP structural component Myosin-X (MYO10). Using spinning disk and super-resolution microscopy combined with a machine learning approach to phenotype oocyte morphology, we show that the lack of Myo10 decreases TZP density during oocyte growth. Reduction in TZPs does not prevent oocyte growth but impairs oocyte-matrix integrity. Importantly, we reveal by transcriptomic analysis that gene expression is altered in TZP-deprived oocytes, and that oocyte maturation and subsequent early embryonic development are partially affected, effectively reducing mouse fertility. We propose that TZPs play a role in the structural integrity of the germline-somatic complex, which is essential for regulating gene expression in the oocyte and thus its developmental potential.

cell biology↗

bioRxiv2022

An interpretable and versatile machine learning approach for oocyte phenotyping

Meiotic maturation is a crucial step of oocyte development allowing its potential fertilization and embryo development. Elucidating this process is important both for fundamental research and assisted reproductive technology. However, only few computational tools, based on non-invasive measurements, are currently available to characterize oocyte meiotic maturation. Here, we develop a computational framework to phenotype oocytes based on images or movies acquired exclusively in transmitted light. We first trained neural networks to segment the contours of oocytes and their zona pellucida using a diverse cohort of both mouse and human oocytes. We then defined a comprehensive set of morphological features to describe a single oocyte. We have implemented these steps in a versatile and user-friendly open source Fiji plugin available to the mouse and human oocyte community. Then, we present a machine learning pipeline based on selected features to automatically recognize oocyte populations and determine their morphological differences. Its first application is a novel approach to screen oocyte strains and automatically identify their morphological characteristics. We demonstrate its potential by phenotyping a well characterized genetically modified mouse oocyte strain. Its second application is to predict and characterize the maturation potential of oocytes. Importantly, we identify two new features to assess mouse oocyte maturation potential, consisting in the texture of the zona pellucida and the cytoplasmic particles size. Eventually, we tested whether these mouse oocyte quality features were applicable to human oocytes developmental potential.

bioinformatics↗

bioRxiv2021

Cytoplasmic forces functionally reorganize nuclear condensates in oocytes

Cells remodel their cytoplasm with force-generating cytoskeletal motors1. Their activity generates random forces that stir the cytoplasm, agitating and displacing membrane-bound organelles like the nucleus in somatic2-4 and germ5-7 cells. These forces are transmitted inside the nucleus4,7, yet their consequences on liquid-like biomolecular condensates8-10 residing in the nucleus remain unexplored. Here, we probe experimentally and computationally diverse nuclear condensates, that include nuclear speckles, Cajal bodies, and nucleoli, during cytoplasmic remodeling of female germ cells named oocytes. We discover that growing mammalian oocytes deploy cytoplasmic forces to timely impose multiscale reorganization of nuclear condensates for the success of meiotic divisions. These cytoplasmic forces accelerate nuclear condensate collision-coalescence and molecular kinetics within condensates. Inversely, disrupting the forces decelerates nuclear condensate reorganization on both scales, compromising condensate-associated mRNA processing and consequently hindering oocyte divisions that drive female fertility. We establish that cytoplasmic forces can reorganize nuclear condensates in an evolutionary conserved fashion in insects. Our work implies that cells evolved a mechanism, based on cytoplasmic force tuning, to functionally regulate a broad range of nuclear condensates across scales. This finding opens new perspectives when studying condensate-associated pathologies like cancer, neurodegeneration and viral infections11-13.

cell biology↗

bioRxiv2019

Centering based on active diffusion in mouse oocytes is non-specific

The mechanism for nucleus centering in mouse oocytes results from a gradient of actin-positive vesicles. By microinjecting oil droplets and fluorescent beads, we analyze the consequences of the gradient of activity on transport of exogenous tracer particles of different sizes. We also use optical tweezers to probe rheological properties of the cytoplasm. We find that the gradient activity induces a general centering force, akin to an effective pressure gradient, leading to centering of oil droplets with velocities comparable to nuclear ones. High temporal resolution measurements reveal that passive particles, larger than 1{micro}m, experience the activity gradient by a biased diffusion towards the cell center. Unexpectedly, this general and size dependent mechanism is maintained in Meiosis I but contrasted by a further process that specifically off-centers the spindle. These antagonizing processes depend on myosin activity, thus we reconcile how the same molecular actors can have two opposite functions (centering versus off-centering).

cell biology↗

bioRxiv2018

Gene editing can generate fragile bivalents in mouse oocytes

Mouse female meiotic spindles assemble from acentriolar MTOCs (aMTOCs) that fragment into discrete foci. These are further sorted and clustered to form spindle poles, thus providing balanced forces for faithful chromosome segregation. To assess the impact of aMTOCs biogenesis on spindle assembly, we genetically induced their precocious fragmentation in mouse oocytes using conditional overexpression of Plk4, a master MTOC regulator. Excessive microtubule nucleation from these fragmented aMTOCs accelerated spindle assembly dynamics. Prematurely formed spindles promoted the breakage of three different fragilized bivalents, generated by the presence of recombined Lox P sites. Reducing the density of microtubules diminished the extent of chromosome breakage. Thus, improper spindle forces can lead to widely described yet unexplained chromosomal structural anomalies with disruptive consequences on the ability of the gamete to transmit an uncorrupted genome.

cell biology↗

bioRxiv2018

Active fluctuations modulate gene expression in mouse oocytes

In mammals, the nucleus is central in oocytes, not defining the future embryo axis. Nucleus centring depends on an F-actin mediated pressure gradient. In Fmn2-/- oocytes, lacking the F-actin nucleator Formin 2, the nucleus is off-centre and can be centred by re-expressing Formin 2. Here, we addressed the biological significance of nucleus positioning in mammalian oocytes. Using a dedicated computational 3D imaging approach, we observed nuclear architecture alterations in mouse Fmn2-/- oocytes. RNA sequencing of control versus Fmn2-/- oocytes detected 2285 mis-regulated genes. Rescue experiments showed that the process of nuclear positioning impacts nuclear architecture and gene expression. Using signal processing methods coupled to biophysical modelling allowing the extraction of in vivo mechanical properties of the nuclear envelope, we showed that F-actin-mediated activity promotes nuclear envelope shape fluctuations and chromatin motion. We thus propose a mechano-transduction model whereby nucleus positioning via microfilaments modulates oocyte transcriptome, essential for further embryo development.

cell biology↗

bioRxiv2018

Separation and Loss of Centrioles from Primordidal Germ Cells to Mature Oocytes in the Mouse

Oocytes, including those from mammals, lack centrioles, but neither the mechanism by which mature eggs lose their centrioles nor the exact stage at which centrioles are destroyed during oogenesis is known. To answer questions raised by centriole disappearance during oogenesis, using a transgenic mouse expressing GFP-centrin-2 (GFP CETN2), we traced their presence from e11.5 primordial germ cells (PGCs) through oogenesis and their ultimate dissolution in mature oocytes. We show tightly coupled CETN2 doublets in PGCs, oogonia, and pre-pubertal oocytes. Beginning with follicular recruitment of incompetent germinal vesicle (GV) oocytes, through full oocyte maturation, the CETN2 doublets separate within the pericentriolar material (PCM); concomitantly, a rise in single CETN2 pairs is identified. CETN2 dissolution accelerates following meiosis resumption. Remarkably, a single CETN2 pair is retained in the PCM of most meiotic metaphase-I and -II spindle poles. Partial dissolution of the CETN2 foci occurs even as other centriole markers, like Cep135, a protein necessary for centriole duplication, are maintained at the PCM. Furthermore, live imaging demonstrates that the link between the two centrioles breaks as meiosis resumes and that centriole association with the PCM is progressively lost. Microtubule inhibition shows that centriole dissolution is uncoupled from microtubule dynamics. Thus, centriole doublets, present in early G2-arrested meiotic prophase oocytes, begin partial reduction during follicular recruitment and meiotic resumption, much later than previously thought.

developmental biology↗