bims-cebooc 2026-11-08 papers

bims-cebooc

Biomed News

on Cell biology of oocytes

Issue of 2026–11–08
twelve papers selected by
Gabriele Zaffagnini, Universität zu Köln

Comprehensive proteomic profiling reveals mRNA splicing suppression during human oocyte aging.
Modeling of human MLH1 and MLH3 variants in mice reveals novel functions of MutLγ in meiotic DNA repair and the ovarian reserve.
Integrative Single-Cell Proteomics and Network Analysis Identifies DHX9 as a Key Regulator of Oocyte Maturation and a Therapeutic Target for Oocyte Developmental Arrest.
Germ granules function as stress-responsive hubs to protect germ cell resilience.
The making of an egg: Cellular and molecular journeys through human folliculogenesis and oocyte maturation.
Spatial relief of Kinesin-1 auto-inhibition by Ensconsin regulates ncMTOCs localization and shapes microtubule networks.
Germ traCre and Germbow: Cre-Based Transgenic Lineage Tracing Systems to Examine Early Gametogenesis and PGC Germline Contributions in Zebrafish.
Holistic integration of protein interaction datasets establishes a framework for exploring the organization and composition of Caenorhabditis elegans germ granules.
An interaction between Yorkie and Taiman transcriptional coactivators regulates niche-to-stem cell BMP signaling in the female Drosophila germline.
Y chromosome instability in the early mouse embryo.
The Bicaudal-C repression domain couples translational silencing to maternal embryonic patterning.
Mitochondrial subpopulations in oocytes and cumulus cells exhibit distinct age-associated changes and selective plasticity in response to NMN supplementation.

EMBO J. 2026 Nov 02.

Comprehensive proteomic profiling reveals mRNA splicing suppression during human oocyte aging.

Changjian Yin, Zhenzhen Hou, Rusong Zhao, Miaomiao Wang, Shengjie Ling, Chuanxin Zhang, Xiaoou Feng, Shigang Zhao, Zi-Jiang Chen, Keliang Wu, Honghui Zhang, Xuejiang Guo, Han Zhao.

Reproductive aging impairs female fertility, and oocyte aging is considered a major driver of this phenotype, which manifests with increased aneuploidy and miscarriage risk, while no effective treatments have been widely implemented to date. Here, we report comprehensive protein expression profiling of oocytes during human aging, comparing fully grown germinal vesicle oocytes (FGO) and metaphase II (MII) oocytes; we describe the effect of aging on the maturation profiles across multiple age groups, including 25, 30, 35, and 40 years old. This analysis uncovered differential protein dynamics upon aging, with FGOs displaying protein expression alterations as early as 30 years, whereas these changes were delayed until the age of 35 or 40 in MII oocytes, particularly in proteins associated with mRNA splicing, translation, and chromosome segregation. Integration with transcriptomic data revealed suppression of splicing machineries as a potential initiating factor driving oocyte aging, characterized by deficiencies in mitochondrial function and chromosome segregation. This was validated by splicing inhibition, which suppressed mitochondrial function and ROS levels in mouse and human oocytes. Further, splicing factor DHX15 was identified as a candidate regulator of stage-specific oocyte aging. Together, our work systematically delineates the dynamic protein landscapes of human oocytes across multiple age groups, providing molecular targets and potential therapeutic strategies for clinical intervention.

DOI: https://doi.org/10.1038/s44318-026-00921-x
bioRxiv. 2026 Oct 27. pii: 2026.10.26.762008. [Epub ahead of print]

Modeling of human MLH1 and MLH3 variants in mice reveals novel functions of MutLγ in meiotic DNA repair and the ovarian reserve.

Xinbao Ding, Vertika Singh, John C Schimenti.

The mismatch repair proteins MLH1 and MLH3 form the MutLγ complex that is essential for >90% of meiotic crossovers (CO) in mice. Although deletion of either gene causes infertility, we previously found that mouse models of certain human MLH1/3 missense variants caused elevated aneuploidy and progressive loss of female fecundity despite having a normal ovarian reserve. Here, we report that additional missense and null alleles caused significant pre-pubertal follicle loss independent of alterations to meiotic CO levels. Deletion of the DNA damage checkpoint kinase Chek2 (Chk2) partially rescued the oocyte pool of Mlh1- and Mlh3 -deficient mice, indicating that defects in meiotic prophase I triggered oocyte elimination. In spermatocytes, both missense and null alleles caused abnormal γH2AX 'flares' on autosomes during late pachynema and diplonema, extending into chromatin loops from the synaptonemal complex. These flares frequently contained unusually large foci of the ssDNA binding protein RPA as well as DNA end processing factors including CtIP, RAD50 and BLM, consistent with abnormal and extensive DNA resection. The results reveal a previously unrecognized meiotic function of MutLγ in preventing DNA hyper-resection of spontaneous DNA breaks or of persistent recombination intermediates in late prophase I. Together with our previous studies, the results show that MLH1/3 variants can impair fertility through at least three mechanistically distinct routes: severe crossover loss sufficient to activate the metaphase I spindle assembly checkpoint; subthreshold crossover defects that increase aneuploidy and embryo loss; and abnormal late-prophase DNA processing that activates a CHEK2-dependent oocyte quality-control pathway and depletes the ovarian reserve, causing primary ovarian insufficiency (POI). Thus, MutLγ has broader roles in maintaining meiotic genome integrity than can be explained by crossover formation alone.

DOI: https://doi.org/10.64898/2026.10.26.762008
J Proteome Res. 2026 Nov 06. 25(11): 6056-6069

Integrative Single-Cell Proteomics and Network Analysis Identifies DHX9 as a Key Regulator of Oocyte Maturation and a Therapeutic Target for Oocyte Developmental Arrest.

Guang-Yi Cao, Si-Pei Liu, Ao-Lei Guo, Jing-Xin Li, Ru-Yu Jiang, Shan-Shan Wang.

  Oocyte developmental arrest at the germinal vesicle (GV) or metaphase I (MI) stage is a major cause of infertility, yet its molecular mechanisms remain poorly understood. Here, we performed ultradeep single-cell proteomics on 8 human oocytes (4 GV-stage and 4 MI-stage) and 12 mouse oocytes (3 GV, 3 MI, 3 MII, and 3 FGO) to investigate the proteomic landscape of developmental arrest. We identified an average of 5,574 proteins per human oocyte (range: 4,350-6,157) and 3,477 per mouse oocyte (range: 3,315-3,634), revealing aberrant activation of mRNA splicing pathways in arrested oocytes. Integrative network analysis identified the RNA helicase DHX9 as a central hub within a conserved coexpression module. Mechanistically, elevated DHX9 expression maintained transcriptional hyperactivity, preventing the transition to transcriptional quiescence required for maturation. Critically, pharmacological inhibition of DHX9 with ATX968 restored transcriptional silencing and significantly rescued meiotic maturation, achieving 95% GVBD and 80% PBE at 1 μM ATX968, comparable to wild-type controls (98%/82%) and significantly exceeding vehicle-treated arrested oocytes (8% GVBD; p < 0.001). In summary, our study demonstrates that DHX9-driven dysregulation of RNA splicing is a key mechanism underlying oocyte developmental arrest. These findings highlight DHX9 as a promising therapeutic target and provide a potential strategy for improving oocyte competence in clinical infertility treatment.

Keywords:  DHX9; MRNA splicing; Oocyte; Pseudotime trajectory analysis; Single-cell proteomics; Therapy targeted

DOI:  https://doi.org/10.1021/acs.jproteome.6c00419
bioRxiv. 2026 Oct 27. pii: 2026.10.23.761416. [Epub ahead of print]

Germ granules function as stress-responsive hubs to protect germ cell resilience.

Olivia J Gaylord, Misheel Armasanaa, Aritra Basu, Heng-Chi Lee.

Biomolecular condensates are dynamic, membrane-less compartments that perform critical cellular functions in the adaptation to environmental stressors. Within germ cells, germ granules are specialized condensates essential for germ cell viability, genome defense, and epigenetic inheritance. Notably, environmental stressors such as heat and starvation can disrupt genome defense and epigenetic inheritance, yet germ cell viability is often preserved. How germ cells adapt to environmental stress and recover viability remains poorly understood. Here, we investigate the impact of heat stress on the biomolecular condensates of adult germ cells in C. elegans. Upon heat stress, we observe extensive remodeling of the germ granule compartments, including reduced enrichment of key genome defense and epigenetic inheritance factors. Adjacent to remodeled germ granules, stress granules and P-bodies robustly assemble, suggesting these distinct condensates may functionally interact during the stress response. Indeed, we find stress granule and P-body formation within germ cells largely requires germ granule assembly factors GLH-1/VASA and MIP-1. Furthermore, we show these germ granule assembly factors and stress granule factors GTBP-1/G3BP1 and TIAR-1/TIA1, are essential for recovery of germ cell viability after heat stress. Intriguingly, stress granule factor TIAR-1/ TIA1 localizes to germ granules with and without stress, indicating germ granules are poised for the stress response. Together, our results support a model in which germ granules function as stress-responsive hubs that reorganize RNA granule networks to promote germline resilience.

DOI: https://doi.org/10.64898/2026.10.23.761416
Reprod Biol. 2026 Nov 06. pii: S1642-431X(26)00125-7. [Epub ahead of print]27(1): 101303

The making of an egg: Cellular and molecular journeys through human folliculogenesis and oocyte maturation.

Tânia Santos, Ana Margarida Calado, Joana Saramago, Rosália Sá, Mário Sousa.

  Human folliculogenesis has been extensively reviewed, but gaps between morphology and molecular facets remain to be filled. We here detailed update human folliculogenesis at the morphological and molecular aspects and provided a link to oocyte maturation and competence acquisition, and, as well, to the novel findings on oocyte ultrastructure. While human folliculogenesis and oogenesis set the baseline of female fertility, a major challenge remains to bridge the gap between macro-morphological transitions and limited molecular pathways. Here, we provide a comprehensive review of recent conceptual advances in human follicular development, with a focus on emerging regulatory networks such as the Hippo and PI3K/mTOR pathways that regulate primordial follicle dormancy and activation. We combine classic morphological landmarks with recent quantitative stereological data to map the dynamic spatial reorganization of oocyte organelles (mitochondria, smooth endoplasmic reticulum complexes, and cortical vesicles) during prophase-I, metaphase-I and metaphase-II. Furthermore, we emphasize the translational significance of these cellular dynamics by connecting specific molecular checkpoints to clinical problems encountered in assisted reproduction. Understanding these synchronous nuclear-cytoplasmic maturation dynamics offers us important information to optimize in vitro maturation protocols, refine oocyte cryopreservation strategies and improve non-invasive quality assessments in reproductive medicine.

Keywords:  Folliculogenesis; Oocyte competence; Oocyte maturation; Oocyte ultrastructure

DOI:  https://doi.org/10.1016/j.repbio.2026.101303
J Cell Sci. 2026 Nov 04. pii: jcs.265338. [Epub ahead of print]

Spatial relief of Kinesin-1 auto-inhibition by Ensconsin regulates ncMTOCs localization and shapes microtubule networks.

Anne-Marie Berisha, Aude Pascal, Marine Guelle, Clément Bousquet, Denis Chrétien, Laetitia Bataillé, Régis Giet.

  During Drosophila oogenesis, the organization of microtubules (MTs) drives polarized transport and cytoplasmic flows. Although Kinesin-1 plays a central role in these processes, its molecular and spatial regulation remains poorly understood. Here, we show that Ensconsin, an activator of the Kinesin heavy chain (Khc), is enriched in the oocyte through MT binding, Dynein-mediated transport and by the MT-anchoring protein Ninein. Strikingly, loss of Ensconsin enrichment reduces cortical non-centrosomal microtubule-organizing centers (ncMTOCs), weakens MT nucleation, impairs MT organization and MT-dependent cytoplasmic flows. Additionally, a specific Khc variant unable to bind Ensconsin, is constitutively active and is able to partly rescue the loss of Ensconsin in oocyte and neural stem cells, thereby providing in vivo support for the relief-of-auto-inhibition model. Overall, we uncover a novel function for the Khc-Ensconsin complex in the recruitment of ncMTOCs in oocytes for MT organization. Our findings are in line with a model in which Ensconsin enrichment acts as a rheostat to modulate Khc activation, ensuring precise spatial remodeling of the microtubule cytoskeleton in the oocyte.

Keywords:  Drosophila; Ensconsin/MAP7; Kinesin-1; Microtubule; NcMTOC; Oocyte

DOI:  https://doi.org/10.1242/jcs.265338
J Vis Exp. 2026 Oct 30.

Germ traCre and Germbow: Cre-Based Transgenic Lineage Tracing Systems to Examine Early Gametogenesis and PGC Germline Contributions in Zebrafish.

Maya Pahima, Florence L Marlow.

Studies to date on reproductive development and gametogenesis in zebrafish have been limited by the availability of methods to visualize the developing germline. These include transient labeling approaches, such as injection of DNA or RNA encoding germline-localizing markers, or transgenic approaches that leverage germline promoters that are activated only after gonad formation. Degradation of injected elements before germline-specific zygotic promoter activation leaves a period when the early germ cells cannot be reliably labeled and tracked. To bridge this gap, Germ traCre and Germbow were developed: two Cre-based transgenic lineage tracing systems which provide the earliest inducible and targeted long-term labeling of germ cell precursors -primordial germ cells (PGCs) - and their progeny. It was recently demonstrated that the Germ traCre and Germbow systems are effective for investigating PGC differentiation and the establishment of the pre-gametic germline. This cell fate transition is critical for the formation of a functional vertebrate gonad but has largely been inaccessible. Using these systems, we lineage-traced early PGC contributions to the gonad and found that PGCs give rise to a more diverse repertoire of germ cell progeny than anticipated. It was further demonstrated that individual PGC contributions affect ovarian reserve composition and lifelong reproductive potential. Together, these systems permit access to gametogenesis from the earliest germ cell differentiation events to gamete maturation, making them useful systems for germline lineage tracing that can be applied to any stage of reproductive life. This article presents comprehensive protocols for clonal lineage tracing of zebrafish PGCs and their progeny in the developmental day 16 (d16) juvenile zebrafish gonad, as well as multispectral labeling and analysis of ovarian reserve composition in adult females. This study demonstrates how to use the systems and provide methods for staining, dissection, and imaging of the juvenile zebrafish germline.

DOI: https://doi.org/10.3791/69477
Genetics. 2026 Nov 04. pii: iyag305. [Epub ahead of print]

Holistic integration of protein interaction datasets establishes a framework for exploring the organization and composition of Caenorhabditis elegans germ granules.

Carlotta Wills, Alyson Ashe.

  Spatiotemporal organization of biological molecules is a key driver of cellular processes, including many post-transcriptional epigenetic processes. The germline-specific germ granules are biomolecular condensates that act as hubs for mRNA and small RNA processing and are core regulators of germline gene expression programming. Germ granules have been studied extensively in Caenorhabditis elegans, and recent developments have led to many subdivisions of the germ granule into specialized compartments. Rapid advancements in microscopy and protein-protein interaction (PPI) screening techniques have produced a large amount of data towards characterizing the localization of proteins to specific granules. However, common methods used to probe PPIs are limited in their ability to robustly detect valid interactions, especially the multivalent and sometimes transient ones observed in granule environments. Here we perform a meta-analysis of granule protein interaction screens. While these experiments generally enrich for proteins matching the profile of granule-associated proteins, we find that when considering screens individually, reproducibility is surprisingly low, highlighting not only the variability inherent in these methods but also the dynamic nature of the PPI networks present in granules. We developed an algorithm to provide a measure of each protein's association with specific granules across various experiments (a "granule association metric" or GAM). By further clustering and investigation of the GAM matrix, we demonstrate the power of this holistic approach to provide deeper insights into germ granule organization, highlight novel candidates, and act as a resource to inform future investigations into granules and their constituent proteins.

Keywords:   C elegans ; germ granules; meta-analysis; proteomics

DOI:  https://doi.org/10.1093/genetics/iyag305
bioRxiv. 2026 Oct 29. pii: 2026.10.28.762554. [Epub ahead of print]

An interaction between Yorkie and Taiman transcriptional coactivators regulates niche-to-stem cell BMP signaling in the female Drosophila germline.

Chloe Wells, Victoria C Placentra, Shilpi Verghese, Tod Butenschon, Kenneth H Moberg.

Communication between stem cells and their specialized niche microenvironments is vital for organism development and tissue homeostasis. However, mechanisms that limit intracellular signaling within a given niche and thus maintain stem cell fate are not fully understood. The Hippo and Ecdysone nuclear receptor (EcR) pathways are well conserved and individually required in niche cells for the establishment and maintenance of stem cell pools in Drosophila . These pathways are linked in the nucleus via a physical interaction between their respective transcriptional coactivators Yorkie (Yki) and Taiman (Tai). Within the female Drosophila germline niche, Yki and Tai each regulate behavior of stem cells and their progeny. It is not known whether these roles are mechanistically distinct or are a product of a physical interaction between Yki and Tai that enables a common niche-support role. Here we utilize a CRISPR mutant fly line containing a form of Tai unable to bind Yki ( tai PPxA ) to examine requirements for the Yki:Tai interaction in vivo . We find that the Yki:Tai interaction controls the GSC niche mainly through a role in escort cells (ECs), a key somatic cell-type that ensheathes the niche and regulates intercellular signaling. tai PPxA reduces EC cytoplasmic processes and allows the Dpp ligand to spread beyond its normally restricted range within the GSC niche, which elevates Dpp signaling and blocks differentiation of GSC progeny. In sum, these findings suggest that a Yki:Tai interaction facilitates crosstalk between the Hippo and EcR pathways within ECs and thus plays a critical role in maintaining intercellular signals that allow somatic cells to shape the niche microenvironment.

DOI: https://doi.org/10.64898/2026.10.28.762554
Sci Adv. 2026 Nov 06. 12(45): eaej3098

Y chromosome instability in the early mouse embryo.

Agata P Zielinska, Richelle Rietdijk, Valdone Maciulyte, Aurelien Courtois, James M A Turner.

The Y chromosome lacks canonical centromeric repeats necessary for high-fidelity chromosome segregation. In adult tissues, this causes Y loss and predisposes to disease. However, its impact on embryogenesis is unknown. Here, we identify the first mouse embryonic mitoses as a window during which the Y centromere is unusually weak. This vulnerability impairs kinetochore strength and the Y becomes preferentially trapped at the spindle pole, resulting in missegregation. To study the impact of Y loss, we generate an aggregation model to track specific aneuploidies in mosaic embryos. Loss of the Y slows down cell division and compromises embryo size. Our findings reveal a developmental window during which the Y is especially vulnerable to loss, with implications for male sex determination and the origin of Turner syndrome (XO).

DOI: https://doi.org/10.1126/sciadv.aej3098
Development. 2026 Nov 06. pii: dev.205916. [Epub ahead of print]

The Bicaudal-C repression domain couples translational silencing to maternal embryonic patterning.

Charlotte R Kanzler, Emily T Johnson-Sheehan, Douglas W Houston, Olivia Aberle, Axel Schweickert, Michael D Sheets.

  The maternal period of embryonic development occurs before zygotic transcription is active and therefore relies heavily on post-transcriptional mechanisms such as regulated mRNA translation. Central to this regulation are RNA-binding proteins (RBPs), yet how individual RBPs orchestrate maternal gene regulation remains poorly understood. Bicaudal-C (Bicc1) is a conserved RBP and translational repressor that selects mRNAs through N-terminal KH domains and represses their translation through C-terminal activities whose mechanisms remain unclear. In the maternal Xenopus embryo, Bicc1 represses mRNAs encoding cell-fate regulators to establish the anterior/posterior axis. Here, we define the activities of the Bicc1 repression domain (Bicc1-RD). We show that the RD is sufficient for poly(A)-independent translational repression and mediates interactions with diverse RNA regulatory factors, including Bicc1 itself, the CCR4-NOT complex, and the translational regulators Lsm14, 4E-T, and Ddx6. Functional analyses reveal that RD activities are essential for maternal Bicc1-dependent patterning but dispensable for its zygotic role in left/right patterning, demonstrating mechanistically distinct Bicc1 repression strategies across developmental stages. These findings reveal how a modular RBP can coordinate stage-specific translational control during embryogenesis.

Keywords:  Anterior-posterior patterning; Maternal embryo; RNA binding; RNA repression; Translational regulation

DOI:  https://doi.org/10.1242/dev.205916
J Ovarian Res. 2026 Aug 07. pii: 332. [Epub ahead of print]19(1):

Mitochondrial subpopulations in oocytes and cumulus cells exhibit distinct age-associated changes and selective plasticity in response to NMN supplementation.

Andrew J Piasecki, Hannah Sheehan, Paula Ledo Hopgood, Jonathan L Tilly, Dori C Woods.

   BACKGROUND: Mitochondrial dysfunction is a leading contributor to the decline in oocyte quality associated with maternal aging. Prior investigations of mitochondrial function in the ovarian follicle have largely treated the mitochondrial pool as a homogeneous population, reporting aggregate values that may obscure biologically meaningful differences between distinct mitochondrial subpopulations. The present study addresses this limitation by characterizing mitochondrial subpopulation dynamics in oocytes and cumulus granulosa cells at single-organelle resolution using fluorescence-activated mitochondria sorting (FAMS).
RESULTS: Analysis of the aggregate mitochondrial population in mouse oocytes revealed no significant age-associated differences in mitochondrial DNA copy number or membrane potential, a result that would previously have been interpreted as evidence of minimal age-related mitochondrial change. Subpopulation analysis revealed this conclusion to be incomplete: aged oocytes showed significantly elevated mitochondrial DNA copy number specifically within the high membrane potential and small mitochondrial subpopulations, with no significant differences in the low membrane potential or large subpopulations. NMN supplementation normalized mitochondrial DNA copy number in the high membrane potential and small subpopulations toward young levels while producing an opposing effect in large mitochondria, demonstrating subpopulation-specific rather than uniform rejuvenation. In cumulus cells, significant age-associated changes were detectable at the aggregate level, including a reduction in mitochondrial DNA copy number and an elevation in membrane potential, and subpopulation analysis further resolved these findings. The age-associated reduction in cumulus cell mitochondrial DNA copy number was driven predominantly by the high membrane potential subpopulation. NMN supplementation exerted opposing effects on small and large cumulus cell mitochondrial subpopulations, increasing mitochondrial DNA copy number above both young and aged levels in small mitochondria while further reducing it below aged levels in large mitochondria.
CONCLUSIONS: Viewing the mitochondrial pool as a heterogeneous mixture of functionally distinct subpopulations rather than a uniform population reveals age-associated alterations in oocytes and cumulus cells that are undetectable by aggregate analysis. NMN supplementation exerts subpopulation-specific effects in both cell types, identifying specific mitochondrial subtypes as more precise targets for future mechanistic investigation of age-associated infertility than the mitochondrial pool considered in aggregate.

Keywords:  Cumulus granulosa cells; Membrane potential; Mitochondrial heterogeneity; NMN; Oocyte quality; Reproductive aging; mtDNA

DOI:  https://doi.org/10.1186/s13048-026-02223-6