bims-cebooc Biomed News
on Cell biology of oocytes
Issue of 2026–08–09
six papers selected by
Gabriele Zaffagnini, Universität zu Köln
  1. Cell size reduction distinctly scales spindle elongation and chromosome segregation in C. elegans.
  2. High-resolution mapping of embryonic genome activation unveils a decoupling of transcription activation from precocious H3K4me3 removal.
  3. Bruno 1 remodels P-bodies to protect select mRNAs during the early ER stress response.
  4. CtBP1/2 restrict DUX-dependent and independent 2C-like programs in mouse embryonic stem cells.
  5. Protocol for culture of zebrafishdeveloping ovaries as an ex vivo system for investigating early oogenesis and ovarian development.
  6. PARP7-mediated mono-ADP-ribosylation stabilizes MYH9 to ensure actin cap integrity and chromosome segregation in mouse oocytes.
  1. Nat Commun. 2026 Aug 06. pii: 7929. [Epub ahead of print]17(1):
    Cell size reduction distinctly scales spindle elongation and chromosome segregation in C. elegans.
    Chukwuebuka William Okafornta, Reza Farhadifar, Gunar Fabig, Hai-Yin Wu, Maria Köckert, Martin Vogel, Daniel Baum, Robert Haase, Michael J Shelley, Daniel J Needleman, Thomas Müller-Reichert.
      How embryos adapt their internal cellular machinery to reductions in cell size during development remains a fundamental question in cell biology. Here, we use high-resolution lattice light-sheet fluorescence microscopy and automated image analysis to quantify lineage-resolved mitotic spindle and chromosome segregation dynamics from the 2- to 64-cell stages in Caenorhabditis elegans embryos. While spindle length scales with cell size across both wild-type and size-perturbed embryos, chromosome segregation dynamics remain largely invariant, suggesting that distinct mechanisms govern these mitotic processes. Combining femtosecond laser ablation with large-scale electron tomography, we find that mid-spindle microtubules mediate chromosome segregation dynamics and remain uncoupled from cell size across all stages of early development. In contrast, spindle elongation is driven by cortically anchored motor proteins and astral microtubules, rendering it sensitive to cell size. Incorporating these experimental results into an extended stoichiometric model for both the spindle and chromosomes, we find that allowing only cell size and microtubule catastrophe rates to vary reproduces spindle pole-to-pole dynamics across development. The same model also accounts for centrosome separation and pronuclear positioning in the one-cell C. elegans embryo, spindle-length scaling across nematode species spanning ~100 million years of divergence, and spindle rotation in human cells. Thus, a unified stoichiometric framework provides a predictive, mechanistic account of spindle and nuclear dynamics across scales and species.
    DOI:  https://doi.org/10.1038/s41467-026-76360-3
  2. Sci Adv. 2026 Aug 07. 12(32): eaec9545
    High-resolution mapping of embryonic genome activation unveils a decoupling of transcription activation from precocious H3K4me3 removal.
    Jasmina Al-Mousawi, Luca Michetti, Laura Castaldi, Na Liu, Laura Villacorta, Vladimir Benes, Ana Boskovic.
      The lack of temporal resolution in transcriptomic data during mammalian embryonic genome activation (EGA) has precluded the comprehensive understanding of the functional relationships between the various gene regulatory mechanisms governing this process. Here, we finely dissect the transcriptional dynamics of mouse EGA using precision in vitro fertilization (IVF) coupled with single-embryo RNA sequencing. Our highly temporally resolved dataset uncovers an extensive, step-wise remodeling of the embryonic messenger RNA landscape, affecting ∼30% of the total detectable transcripts over a 9-hour time frame. We capture the gradual shift from maternal to embryonic messenger RNAs, successfully identify ribosome biogenesis and translation as hallmarks of EGA, and find previously unidentified gene expression dynamics. We further uncover a set of eight histone demethylating enzymes among the earliest up-regulated EGA genes and leverage our precision-IVF to dissect the transcriptional versus developmental impact of histone H3 lysine-4 trimethylation (H3K4me3) remodeling after fertilization. Our results indicate that precocious removal of H3K4me3 from embryonic chromatin only modestly affects embryonic transcription without perturbing EGA timing, arguing against a major instructive role of precocious remodeling of maternally inherited H3K4me3 after fertilization on genome activation. High-resolution transcriptome mapping coupled with functional perturbations allows us to distinguish direct gene expression effects from general impacts on developmental timing, opening avenues for further quantitative characterization of the impact of epigenome remodeling on embryonic transcription.
    DOI:  https://doi.org/10.1126/sciadv.aec9545
  3. Life Sci Alliance. 2026 Oct;pii: e202603806. [Epub ahead of print]9(10):
    Bruno 1 remodels P-bodies to protect select mRNAs during the early ER stress response.
    Samantha N Milano, Livia V Bayer, Julie J Ko, Gwendolyn S Posner, Albina H Granovsky, Diana P Bratu.
      P-bodies are cytoplasmic membraneless organelles involved in mRNA storage, yet their role in cellular stress responses remains unresolved. Here, we demonstrate that P-bodies are remodeled during the early response to ER stress throughout Drosophila melanogaster oogenesis. Notably, this remodeling occurs within minutes of stress induction and precedes stress granule formation. This early remodeling is characterized by changes in P-body morphology and internal organization and promotes selective mRNA storage. Mechanistically, we find that this process is driven by transcriptional up-regulation of the RNA-binding protein, Bruno 1, downstream of ATF4-dependent stress signaling, thereby establishing a connection between the unfolded protein response and condensate regulation. Consistent with this model, loss of Bruno 1 abolishes, whereas its overexpression enhances, P-body remodeling, demonstrating that stress-induced changes in RNA-binding protein levels can reprogram condensate properties. Together, our findings reveal that P-bodies function as stress-responsive hubs enabling selective preservation of essential mRNAs during ER stress. More broadly, this work uncovers a previously unrecognized mechanism by which stress signaling pathways reorganize cytoplasmic architecture to shape mRNA fate.
    DOI:  https://doi.org/10.26508/lsa.202603806
  4. EMBO Rep. 2026 Aug 03.
    CtBP1/2 restrict DUX-dependent and independent 2C-like programs in mouse embryonic stem cells.
    Kazuma Yoshioka, Maki Ichisakino, Kota Sugiyama, Nao Hayakawa, Selma Alamanda Abadi, Heekyoung Yoon, Miyu Marutani, Ryo Masuda, Kyo Takahashi, Yoshiyuki Seki.
      After fertilization, maternally deposited mRNAs are cleared, and de novo transcription is initiated through zygotic genome activation (ZGA), a core event of the maternal-to-zygotic transition in mice. 2-cell-like cells (2CLCs), a rare MERVL-positive subpopulation of mouse embryonic stem cells, partially recapitulate transcriptional features of 2-cell embryos. Although canonical MERVL-high 2CLCs depend on DUX, Dux knockout embryos can develop to term, suggesting that 2CLC models do not fully capture DUX-independent pathways associated with preimplantation transcriptional programs. Here, we show that disruption of C-terminal binding protein 1/2 (Ctbp1/2) activates both DUX-dependent minor ZGA-associated genes and DUX-independent major ZGA- and post-ZGA-associated programs. Pramel7 is derepressed independently of DUX and contributes to subsets of both programs. PRAMEL7 overexpression partially rescues transcriptional defects caused by Dux deletion and is associated with UHRF1 downregulation and DNA demethylation-linked activation of post-ZGA-associated genes. These findings identify CtBP1/2 as repressors of multiple early embryonic transcriptional programs in mouse embryonic stem cells.
    DOI:  https://doi.org/10.1038/s44319-026-00881-7
  5. STAR Protoc. 2026 Aug 05. pii: S2666-1667(26)00411-9. [Epub ahead of print]7(3): 104758
    Protocol for culture of zebrafishdeveloping ovaries as an ex vivo system for investigating early oogenesis and ovarian development.
    Amal Shawahny, Yoel Bogoch, Yaniv M Elkouby.
      A fundamental understanding of early oogenesis is lacking, and zebrafish serve as an excellent model for investigation, based largely on in vivo approaches. We present a protocol for long-term zebrafish ovary culture that supports physiological early oogenesis ex vivo, enabling new experimental approaches. We outline procedures for culture plate and media preparation, ovary dissection, embedding-media-free mounting, and culture handling. In addition, we describe workflows for ovary evaluation and rapid functional assays. For complete details on the use and execution of this protocol, please refer to Shawahny et al.1.
    Keywords:  Cell Biology; Developmental biology; High Throughput Screening; Microscopy; Model Organisms; Molecular Biology
    DOI:  https://doi.org/10.1016/j.xpro.2026.104758
  6. J Adv Res. 2026 Aug 07. pii: S2090-1232(26)00621-1. [Epub ahead of print]
    PARP7-mediated mono-ADP-ribosylation stabilizes MYH9 to ensure actin cap integrity and chromosome segregation in mouse oocytes.
    Guangyi Cao, Sipei Liu, Yanbo Liu, Anqi Chen, Qian Xu, Lina Yu, Aolei Guo, Yan Mao, Ganggui Lou, Chaojun Li, Luhong Wen, Guijun Yan, Haixiang Sun.
       INTRODUCTION: Oocyte meiotic maturation requires highly asymmetric cell division, governed by spindle migration and actin cap formation. However, the upstream mechanisms that regulate the precise coordination of these events remain unclear.
    OBJECTIVES: This study aimed to elucidate the role of PARP7, a mono-ADP-ribosyltransferase, in regulating actin cytoskeletal dynamics and chromosomal stability during mouse oocyte meiosis.
    METHODS: Metabolomic profiling was performed to assess NAD+ dynamics during meiosis. PARP7 expression and localisation were analysed using genetic knockdown and pharmacological inhibition approaches. Multi-omics analyses were performed to identify PARP7 targets and map MARylation sites within the motor domain. Protein stability was evaluated following PARP7 suppression and site-directed mutagenesis.
    RESULTS: PARP7 was identified as the most abundant PARP family member in oocytes and localised to the actin cap during anaphase I. PARP7 inhibition disrupted meiotic progression, resulting in cytokinesis failure, aberrant polar body extrusion, and increased aneuploidy. These defects were attributed to impaired actin cap formation. MYH9 was identified as a PARP7 target, and MARylation was found to be critical for its stability; loss of this modification accelerated MYH9 degradation.
    CONCLUSION: PARP7-mediated MARylation stabilises MYH9 to maintain actin cap integrity and chromosomal segregation in mouse oocytes. These findings provide novel insights into the aetiology of oocyte aneuploidy and age-related reproductive decline.
    Keywords:  Actin dynamics; Asymmetric division; Meiosis; NAD(+); Oocyte
    DOI:  https://doi.org/10.1016/j.jare.2026.08.012
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