Tessandier, N. | bioRxiv Science

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↗

bioRxiv2024

Resource landscape shapes the composition and stability of the human vaginal microbiota

The vaginal microbiota is associated with the health of women and newborns alike. Despite its comparatively simple composition relative to other human microbiota systems, the mechanisms underpinning the dynamics and stability of vaginal microbial communities remain elusive. A crucial, yet so far underexplored, aspect of vaginal microbiota ecology is the role played by nutritional resources. Glycogen and its derivatives, produced by vaginal epithelia, are accessible to all bacterial constituents of the microbiota. Concurrently, free sialic acid and fucose offer supplementary nutritional resources to bacterial strains capable of cleaving them from glycans, which are structurally integral to mucus. Notably, bacteria adept at sialic acid exploitation are often correlated with adverse clinical outcomes and are frequently implicated in bacterial vaginosis (BV). In this study, we introduce a novel mathematical model tailored to human vaginal microbiota dynamics to explore the interactions between bacteria and their respective nutritional landscape. Our resource-based model examines the impact of the relative availability of glycogen derivatives (accessible to all bacterial species) and sialic acid (exclusive to some BV-associated bacteria) on the composition of the vaginal microbiota. Our findings elucidate that the success of BV-associated bacteria is intricately linked to their exclusive access to specific nutritional resources. This private access fortifies communities dominated by BV-associated bacteria, rendering them resilient to compositional transitions. We empirically corroborate our model prediction with longitudinal clinical data on microbiota composition and previously unpublished metabolomic profiles obtained from a North American cohort. The insights gleaned from this study shed light on potential pathways for BV prevention and treatment. Significance statementThe vaginal microbiota has a notable impact on womens health at various stages of life, namely puberty, infection protection, sexual health, fertility, pregnancy, and menopausal changes. At present, most non-anti-microbial products developed to mitigate adverse vaginal symptoms emphasise competitive interactions through acids (boric or lactic acid) or probiotics as a means to "rebalance" microbiota communities. Despite recent advances in profiling the composition of vaginal microbiota communities, there remains a major gap in our mechanistic understanding of how to maintain or reinstate a resilient Lactobacillus-dominated microbiota that improves vaginal health and outcomes. This study explores the role of nutritional resources in the vaginal microbiota by introducing a mathematical model that analyses how access to specific nutrients like glycogen derivatives and sialic acid affects the balance of bacterial vaginosis (BV) and non-BV-associated bacteria. Our findings, supported by original cohort-derived microbiological and metabolomics data, demonstrate that exclusive access to these nutrients is linked to the dominance and resilience of BV-associated bacteria, providing new insights for BV prevention and treatment.

microbiology↗