Biology subjects

Gibeaux, R.

Publications and source records attributed to Gibeaux, R..

10 recordsLinked to original sources

bioRxiv2026

An internal scaffold supports microtubule architectural diversity in Xenopus spermatids

During spermiogenesis, early round spermatids differentiate into specialized spermatozoa through an extensive reshaping of the nucleus driven by coordinated cytoskeletal and chromatin-based mechanisms. In mammals, this process critically relies on the transient manchette, a microtubule-based structure that remodels the spermatid nucleus and serves a track to transport material required for flagellum assembly. However, the existence, organization, and molecular composition of such a structure in other vertebrates have remained poorly investigated. Here, we establish that an organized microtubule network is present in Xenopus spermatids and shares key architectural and molecular hallmarks of the mammalian manchette. We further uncover a large structural heterogeneity of spermatid microtubules, with variable protofilament numbers, skew angles, and lattice organizations. We reveal the presence of a Spaca9-Saxo2 internal scaffold in spermatid microtubules suggesting an internal reinforcement mechanism necessary for extensive nuclear reshaping and cytoplasm remodeling.

cell biology↗

bioRxiv2024

Optimized expansion microscopy reveals species-specific spindle microtubule organization in Xenopus egg extracts

The spindle is a key structure in cell division as it orchestrates the accurate segregation of genetic material. While its assembly and function are well-studied, the mechanisms regulating spindle architecture remain elusive. In this study, we investigate the differences in spindle organization between Xenopus laevis and Xenopus tropicalis, leveraging expansion microscopy (ExM) to overcome the limitations of conventional imaging techniques. We optimized an ExM protocol tailored for Xenopus egg extract spindles, improving upon fixation, denaturation and gelation methods to achieve higher resolution imaging of spindles. Our protocol preserves spindle integrity and allows effective pre-expansion immunofluorescence. This method enabled detailed analysis of the differences in microtubule organization between the two species. X. laevis spindles overall exhibited a broader range of bundle sizes, while X. tropicalis spindles contained mostly smaller bundles. Moreover, while both species exhibited larger bundle sizes near and at the spindle center, X. tropicalis spindles otherwise consisted of very small bundles, and X. laevis spindles medium-sized bundles. By enhancing resolution and minimizing distortions and fixation artifacts, our optimized ExM approach offers new insights into spindle morphology and provides a robust tool for studying the structural intricacies of these large cellular assemblies. This work advances our understanding of spindle architecture and opens up new avenues for exploring underlying mechanisms. SIGNIFICANCE STATEMENTO_LICorrect spindle morphology is key to its function; however, traditional microscopy methods limit our view of spindle architecture. This study addresses the gap in resolving detailed spindle microtubule organization by using advanced imaging. C_LIO_LIThe research utilizes Expansion Microscopy (ExM) to reveal previously unobservable details of spindle morphology in egg extracts of two Xenopus species (X. laevis and X. tropicalis). This approach provides unprecedented clarity on microtubule arrangement and variations in spindle architecture. C_LIO_LIThis work establishes a new protocol for high-resolution imaging of spindle structures, offering insights into how spindle architecture is adapted in differently-sized spindles to ensure proper function. C_LI

cell biology↗

bioRxiv2024

Sperm derived H2AK119ub1 is required for embryonic development in Xenopus Laevis

Deposition of H2AK119ub1 by the polycomb repressive complexe-1 plays a key role in the initiation of facultative heterochromatin formation in somatic cells. Here we evaluate the contribution of sperm derived H2AK119ub1 to embryo development. In Xenopus laevis we found that H2AK119ub1 is present during spermiogenesis and into early embryonic development, highlighting its credential for a role in the transmission of epigenetic information from the sperm to the embryo. In vitro treatment of sperm with USP21, a H2AK119ub1 deubiquitylase, just prior to injection to egg, results in developmental defects associated with gene upregulation. Sperm H2AK119ub1 editing disrupts egg factor mediated paternal chromatin remodelling processes. It leads to post-replication accumulation of H2AK119ub1 on repeat element of the genome instead of CpG islands. This shift in post-replication H2AK119ub1 distribution triggered by sperm epigenome editing entails a loss of H2AK119ub1 from genes misregulated in embryos derived from USP21 treated sperm. We conclude that sperm derived H2AK119ub1 instructs egg factor mediated epigenetic remodelling of paternal chromatin and is required for embryonic development.

developmental biology↗

bioRxiv2021

Structural heterogeneity of the microtubule lattice

Microtubules are tubes of about 25 nm in diameter that are critically involved in a variety of cellular functions including motility, compartmentalization, and division. They are considered as pseudo-helical polymers whose constituent {beta}-tubulin heterodimers share lateral homotypic interactions, except at one unique region called the seam. Here, we used a segmented sub-tomogram averaging strategy to reassess this paradigm and analyze the organization of the {beta}-tubulin heterodimers in microtubules assembled from purified porcine brain tubulin in the presence of GTP and GMPCPP, and in Xenopus egg cytoplasmic extracts. We find that in all conditions, microtubules incorporate variable protofilament and/or tubulin subunit helical-start numbers, as well as variable numbers of seams. Strikingly, the seam number and location vary along individual microtubules, generating holes of one to a few subunits in size within their lattices. Together, our results reveal that the formation of mixed and discontinuous microtubule lattices is an intrinsic property of tubulin that requires the formation of unique lateral interactions without longitudinal ones. They further suggest that microtubule assembly is tightly regulated in a cytoplasmic environment.

cell biology↗

bioRxiv2020

Drosophila dTBCE recruits tubulin around chromatin to promote mitotic spindle assembly

Proper assembly of mitotic spindles requires microtubule nucleation at centrosomes but also around chromatin. In this study, we reveal a novel mechanism by which an enrichment of tubulin in the nuclear space following nuclear envelope breakdown promotes nucleation of spindle microtubules. This event mediated by the tubulin-specific chaperone dTBCE, depends on its tubulin binding CAP-Gly motif and is regulated by Ran. Live imaging, proteomic and biochemical analyses suggest that dTBCE is enriched in the nucleus at nuclear envelope breakdown and interacts with nuclear pore proteins and the Ran machinery to create an environment that facilitates subsequent tubulin enrichment. We propose that dTBCE-dependent increase in tubulin concentration in the nuclear space is an important mechanism for microtubule nucleation in organisms where compartmentalization prevents free diffusion of tubulin.

cell biology↗

bioRxiv2018

Cytoskeleton mechanics determine resting size and activation dynamics of platelets.

Platelets are cell fragments of various size that help maintain hemostasis. The way platelets respond during a clotting process is known to depend on their size, with important physiological consequences. We characterized the cytoskeleton of platelets as a function of their size. In resting Human and Mice platelets, we find a quadradic law between the size of a platelet and the amount of microtubule polymer it contains. We further estimate the length and number of microtubules in the marginal band using Electron and Super-resolution microscopy. In platelets activated with ADP, the marginal band coils as a consequence of cortical contraction driven by actin. We observe that this elastic coiling response is accompanied by a reversible shortening of the marginal band. Moreover, larger platelets have a higher propensity to coil. These results establish the dynamic equilibrium that is responsible for platelet size and differential response on a more quantitative level.\n\nHighlightsO_LIPlatelet size scales consistently with amount of polymerized tubulin in both mouse and human.\nC_LIO_LIPolymerized actin is required for ADP-induced marginal band coiling.\nC_LIO_LIUpon activation, the marginal band exhibits a reversible visco-elastic response involving shortening.\nC_LIO_LILarger marginal bands have a higher propensity to coil than shorter ones.\nC_LI\n\nIn briefThe cytoskeleton is adapted to platelet size and its mechanical properties determine propensity of a platelet to undergo morphological changes in response to agonists.

cell biology↗

bioRxiv2018

Xenopus hybrids provide insight into cell and organism size control

Determining how size is controlled is a fundamental question in biology that is poorly understood at the organismal, cellular and subcellular levels. The Xenopus species, X. laevis and X. tropicalis differ in size at all three of these levels. Despite these differences, fertilization of X. laevis eggs with X. tropicalis sperm gives rise to viable hybrid animals that are intermediate in size. We observed that although hybrid and X. laevis embryogenesis initiates from the same sized zygote and proceeds synchronously through development, hybrid animals were smaller by the tailbud stage, and a change in the ratio of nuclear size to cell size was observed shortly after zygotic genome activation (ZGA), suggesting that differential gene expression contributes to size differences. Transcriptome analysis at the onset of ZGA identified twelve transcription factors paternally expressed in hybrids. A screen of these X. tropicalis factors by expression in X. laevis embryos revealed that Hes7 and Ventx2 significantly reduced X. laevis body length size by the tailbud stage, although nuclear to cell size scaling relationships were not affected as in the hybrid. Together, these results suggest that transcriptional regulation contributes to biological size control in Xenopus.

developmental biology↗

bioRxiv2018

Spindle assembly in egg extracts of the Marsabit clawed frog, Xenopus borealis

Egg extracts of the African clawed frog Xenopus laevis have provided a cell-free system instrumental in elucidating events of the cell cycle, including mechanisms of spindle assembly. Comparison with extracts from the diploid Western clawed frog, Xenopus tropicalis, which is smaller at the organism, cellular and subcellular levels, has enabled the identification of spindle size scaling factors. We set out to characterize the Marsabit clawed frog, Xenopus borealis, which is intermediate in size between the two species, but more recently diverged in evolution from X. laevis than X. tropicalis. X. borealis eggs were slightly smaller than those of X. laevis, and slightly smaller spindles were assembled in egg extracts. Interestingly, microtubule distribution across the length of the X. borealis spindles differed from both X. laevis and X. tropicalis. Extract mixing experiments revealed common scaling phenomena among Xenopus species, while characterization of spindle factors katanin, TPX2, and Ran indicate that X. borealis spindles possess both X. laevis and X. tropicalis features. Thus, X. borealis egg extract provides a third in vitro system to investigate interspecies scaling and spindle morphometric variation.

cell biology↗

bioRxiv2017

Regulatory remodeling in the allo-tetraploid frog Xenopus laevis

BackgroundGenome duplication has played a pivotal role in the evolution of many eukaryotic lineages, including the vertebrates. The most recent vertebrate genome duplication is that in Xenopus laevis, resulting from the hybridization of two closely related species about 17 million years ago [1]. However, little is known about the consequences of this duplication at the level of the genome, the epigenome and gene expression.\n\nResultsOf the parental subgenomes, S chromosomes have degraded faster than L chromosomes ever since the genome duplication and until the present day. Deletions appear to have the largest effect on pseudogene formation and loss of regulatory regions. Deleted regions are enriched for long DNA repeats and the flanking regions have high alignment scores, suggesting that non-allelic homologous recombination (NAHR) has played a significant role in the loss of DNA. To assess innovations in the X. laevis subgenomes we examined p300 (Ep300)-bound enhancer peaks that are unique to one subgenome and absent from X. tropicalis. A large majority of new enhancers are comprised of transposable elements. Finally, to dissect early and late events following interspecific hybridization, we examined the epigenome and the enhancer landscape in X. tropicalis x X. laevis hybrid embryos. Strikingly, young X. tropicalis DNA transposons are derepressed and recruit p300 in hybrid embryos.\n\nConclusionsThe results show that erosion of X. laevis genes and functional regulatory elements is associated with repeats and NAHR, and furthermore that young repeats have also contributed to the p300-bound regulatory landscape following hybridization and whole genome duplication.

evolutionary biology↗

bioRxiv2016

Mechanism of Nuclear Movements in a Multinucleated Cell

Multinucleated cells are important in many organisms but the mechanisms governing the movements of nuclei sharing a common cytoplasm are not understood. In the hyphae of the plant pathogenic fungus Ashbya gossypii, nuclei move back and forth, occasionally bypassing each other, and, preventing the formation of nuclear clusters, this is essential for genetic stability. These movements depend on cytoplasmic microtubules emanating from the nuclei, that are pulled by dynein motors anchored at the cortex. Using 3D stochastic simulations with parameters constrained by the literature, we predict the cortical anchors density from the characteristics of nuclear movements. Altogether, the model accounts for the complex nuclear movements seen in vivo, using a minimal set of experimentally determined ingredients. Interestingly, these ingredients power the oscillations of the anaphase spindle in budding yeast, but in A. gossypii this system is not restricted to a specific nuclear cycle stage, possibly as a result of adaptation to hyphal growth and multinuclearity.

cell biology↗