bims-cebooc Biomed News
on Cell biology of oocytes
Issue of 2025–02–09
nine papers selected by
Gabriele Zaffagnini, Universität zu Köln
  1. Cytoplasmic flow is a cell size sensor that scales anaphase.
  2. CDK1 mediates the metabolic regulation of DNA double-strand break repair in metaphase II oocytes.
  3. OoCount: A Machine-Learning Based Approach to Mouse Ovarian Follicle Counting and Classification.
  4. Characterization of tubulin post-translational modifications and their enzymes during human oocyte meiosis.
  5. Inhibition of ferroptosis counteracts the advanced maternal age-induced oocyte deterioration.
  6. Asymmetric partitioning of persistent paternal mitochondria during cell divisions safeguards embryo development and mitochondrial inheritance.
  7. Chromatin remodeler CHD4 establishes chromatin states required for ovarian reserve formation, maintenance and male germ cell survival.
  8. Nucleoporins shape germ granule architecture and balance small RNA silencing pathways.
  9. Germ granule-mediated mRNA storage and translational control.
  1. Nat Cell Biol. 2025 Jan 31.
    Cytoplasmic flow is a cell size sensor that scales anaphase.
    Olga Afonso, Ludovic Dumoulin, Karsten Kruse, Marcos Gonzalez-Gaitan.
      During early embryogenesis, fast mitotic cycles without interphase lead to a decrease in cell size, while scaling mechanisms must keep cellular structures proportional to cell size. For instance, as cells become smaller, if the position of nuclear envelope reformation (NER) did not adapt, NER would have to occur beyond the cell boundary. Here we found that NER position in anaphase scales with cell size via changes in chromosome motility, mediated by cytoplasmic flows that themselves scale with cell size. Flows are a consequence of friction between viscous cytoplasm and bulky cargo transported by dynein on astral microtubules. As an emerging property, confinement in cells of different sizes yields scaling of cytoplasmic flows. Thus, flows behave like a cell geometry sensor: astral microtubules approach the boundary causing flow velocity changes, which then affect the velocity of chromosome separation, thus scaling NER.
    DOI:  https://doi.org/10.1038/s41556-024-01605-6
  2. BMC Biol. 2025 Feb 06. 23(1): 37
    CDK1 mediates the metabolic regulation of DNA double-strand break repair in metaphase II oocytes.
    Tian-Jin Xia, Feng-Yun Xie, Juan Chen, Xiao-Guohui Zhang, Sen Li, Qing-Yuan Sun, Qin Zhang, Shen Yin, Xiang-Hong Ou, Jun-Yu Ma.
       BACKGROUND: During oocyte maturation, DNA double-strand breaks (DSBs) can decrease oocyte quality or cause mutations. How DSBs are repaired in dividing oocytes and which factors influence DSB repair are not well understood.
    RESULTS: By analyzing DSB repair pathways in oocytes at different stages, we found that break-induced replication (BIR) and RAD51-mediated homology-directed repair (HDR) were highly active in germinal vesicle breakdown (GVBD) oocytes but suppressed in metaphase II (MII) oocytes and the BIR in oocytes was promoted by CDK1 activity. By culturing oocytes in different media, we found that high-energy media, such as DMEM, decreased CDK1 protein levels and suppressed BIR or HDR in MII oocytes. In contrast, 53BP1-mediated nonhomologous end joining (NHEJ) repair was inhibited in germinal vesicle (GV) and GVBD oocytes but promoted in MII oocytes, and NHEJ was not affected by DMEM medium and CDK1 activity. In addition, in DSB MII oocytes, polymerase theta-mediated end joining (TMEJ) was found to be suppressed by CDK1 activity and promoted by high-energy media.
    CONCLUSIONS: In summary, MII oocytes exhibit high heterogeneity in DSB repair, which is regulated by both metabolic factors and CDK1 activity. These results not only expand our understanding of oocyte DSB repair but also contribute to the modification of in vitro maturation medium for oocytes.
    Keywords:  53BP1; Break-induced replication; Double-strand breaks; Oocytes; RAD51; Theta-mediated end joining
    DOI:  https://doi.org/10.1186/s12915-025-02142-w
  3. Biol Reprod. 2025 Feb 04. pii: ioaf023. [Epub ahead of print]
    OoCount: A Machine-Learning Based Approach to Mouse Ovarian Follicle Counting and Classification.
    Lillian Folts, Anthony S Martinez, Jaelyn A Williams, Corey Bunce, Blanche Capel, Jennifer McKey.
      The number and distribution of follicles in each growth stage provides a reliable readout of ovarian health and function. Leveraging techniques for three-dimensional imaging of ovaries in toto has the potential to uncover total, accurate ovarian follicle counts. Due to the size and holistic nature of these images, counting oocytes is time consuming and difficult. The advent of machine-learning algorithms has allowed for the development of ultra-fast, automated methods to analyze microscopy images. In recent years, these pipelines have become more accessible to non-specialists. We used these tools to create OoCount, a high-throughput, open-source method for automatic oocyte segmentation and classification from fluorescent 3D microscopy images of whole mouse ovaries using a deep-learning convolutional neural network (CNN) based approach. We developed a fast tissue-clearing and imaging protocol to obtain 3D images of whole mount mouse ovaries. Fluorescently labeled oocytes from 3D images were manually annotated in Napari to develop a training dataset. This dataset was used to retrain StarDist using a CNN within DL4MicEverywhere to automatically label all oocytes in the ovary. In a second phase, we utilize Accelerated Pixel and Object Classification, a Napari plugin, to sort oocytes into growth stages. Here, we provide an end-to-end pipeline for producing high-quality 3D images of mouse ovaries and obtaining follicle counts and staging. We demonstrate how to customize OoCount to fit images produced in any lab. Using OoCount, we obtain accurate oocyte counts from each growth stage in the perinatal and adult ovary, improving our ability to study ovarian function and fertility.
    Keywords:  bioimage analysis; follicle counting; machine learning; microscopy; mouse; oocyte; ovary
    DOI:  https://doi.org/10.1093/biolre/ioaf023
  4. Reprod Biomed Online. 2024 Feb 09. pii: S1472-6483(24)00074-9. [Epub ahead of print] 103885
    Characterization of tubulin post-translational modifications and their enzymes during human oocyte meiosis.
    Paraskevi Karamtzioti, Anna Ferrer-Vaquer, Montserrat Barragan, Isabelle Vernos, Rita Vassena, Gustavo Tiscornia.
       RESEARCH QUESTION: What are the profiles of tubulin post-translational modifications (PTM) in the meiotic spindles of oocytes with different developmental competence: in-vivo matured MII oocytes (IVO) versus cumulus-free in-vitro matured germinal vesicles (IVM)?
    DESIGN: Cumulus-free germinal vesicles were matured in vitro and compared with IVO in terms of their tubulin PTM, characterizing tubulin PTM patterns (acetylation, tyrosination, detyrosination, D2-tubulin formation and polyglutamylation) of their meiotic spindles by immunofluorescence and by evaluation of the expression levels of the enzymes involved by quantitative reverse transcription polymerase chain reaction.
    RESULTS: Levels of D2-tubulin, tyrosination and polyglutamylation were similar in IVO and IVM oocytes; acetylation displayed different patterns in both groups, whereas detyrosination was detected only in MII oocytes matured in vivo. The PTM enzyme RNA expression levels in germinal vesicles, IVO and IVM were analysed, as well as in oocytes that failed to mature. Of the 24 PTM enzyme transcripts tested, 17 were present in at least one of the groups under study (aΤΑΤ1, NAA50, HDAC6, SIRT2, TTL, TTLL1, TTLL2, TTLL4, TTLL5, TTLL6, TTLL9, TTLL11, TTLL12, CCP1, CCP5, CCP6, VASH1), of which three were differentially expressed (NAA50, TTLL12, CCP1).
    CONCLUSION: All modifications studied were present in human oocytes regardless of whether their meiotic maturation occurred in vivo or in vitro, except for detyrosination, which was found at low levels in the IVO group, but not in the IVM group. This suggests that the presence of tubulin PTMs may play a role in human oocyte maturation, completion of meiosis and developmental competence.
    Keywords:  Oocyte; Oocyte maturation; Post translational modifications; Spindle; Tubulin
    DOI:  https://doi.org/10.1016/j.rbmo.2024.103885
  5. Cell Death Differ. 2025 Feb 06.
    Inhibition of ferroptosis counteracts the advanced maternal age-induced oocyte deterioration.
    Wenjun Zeng, Feixue Wang, Zhaokang Cui, Yu Zhang, Yu Li, Na Li, Zipeng Mao, Hanwen Zhang, Yiting Liu, Yilong Miao, Shaochen Sun, Yafei Cai, Bo Xiong.
      Ferroptosis, a recently discovered form of programmed cell death triggered by the excessive accumulation of iron-dependent lipid peroxidation products, plays a critical role in the development of various diseases. However, whether it is involved in the age-related decline in oocyte quality remains unexplored. Here, we took advantage of nano-proteomics to uncover that reduced ferritin heavy chain (Fth1) level is a major cause leading to the occurrence of ferroptosis in aged oocytes. Specifically, induction of ferroptosis in young oocytes by its activators RSL3 and FAC, or knockdown of Fth1 all phenocopied the meiotic defects observed in aged oocytes, including failed oocyte meiotic maturation, aberrant cytoskeleton dynamics, as well as impaired mitochondrial function. Transcriptome analysis showed that knockdown of Fth1 affected meiosis-related and aging-related pathways in oocytes. Conversely, inhibition of ferroptosis by its inhibitors or expression of Fth1 improved the quality of aged oocytes. We also validated the effects of ferroptosis on the porcine oocyte quality in vitro. Altogether, we demonstrate the contribution of ferroptosis to the age-induced oocyte defects and evidence that inhibition of ferroptosis might be a feasible strategy to ameliorate the reproductive outcomes of female animals at an advanced age.
    DOI:  https://doi.org/10.1038/s41418-025-01456-0
  6. Dev Cell. 2025 Jan 30. pii: S1534-5807(25)00033-4. [Epub ahead of print]
    Asymmetric partitioning of persistent paternal mitochondria during cell divisions safeguards embryo development and mitochondrial inheritance.
    Songyun Wang, Ding Xue.
      Most eukaryotes inherit only maternal mitochondria. The reasons for paternal mitochondrial elimination and the impacts of persistent paternal mitochondria on animals remain elusive. We show that undegraded paternal mitochondria in autophagy-deficient C. elegans embryos are gradually excluded from germ blastomeres through asymmetric partitioning during cell divisions. The embryonic cortical flow drives anterior-directed movements of paternal mitochondria and contributes to their asymmetric apportioning between two daughter blastomeres. By contrast, autophagosome-enclosed paternal mitochondria cluster around and segregate with centrosomes during mitosis and are rapidly degraded through lysosomes concentrated near centrosomes. Failure to exclude persistent paternal mitochondria from the germ blastomere at first cleavage causes their enrichment in the descendant endomesodermal (EMS) blastomere, leading to elevated reactive oxygen species levels, elongated EMS lineage durations, and increased embryonic lethality, which antioxidant treatments can suppress. Thus, regulated paternal mitochondrial distribution away from germ blastomeres is a fail-safe mechanism, protecting embryo development and maternal mitochondrial inheritance.
    Keywords:  C. elegans; PME; ROS; asymmetric partitioning of mitochondria; autophagy; cortical flow; embryo development; germline blastomere; mitochondrial inheritance; paternal mitochondrial elimination; reactive oxygen species
    DOI:  https://doi.org/10.1016/j.devcel.2025.01.013
  7. Nucleic Acids Res. 2025 Jan 24. pii: gkaf008. [Epub ahead of print]53(3):
    Chromatin remodeler CHD4 establishes chromatin states required for ovarian reserve formation, maintenance and male germ cell survival.
    Yasuhisa Munakata, Mengwen Hu, Yuka Kitamura, Raissa G Dani, Adam L Bynder, Amelia S Fritz, Richard M Schultz, Satoshi H Namekawa.
      The ovarian reserve defines female reproductive lifespan, which in humans spans decades due to the maintenance of meiotic arrest in non-growing oocytes (NGOs) residing in primordial follicles. Unknown is how the chromatin state of NGOs is established to enable long-term maintenance of the ovarian reserve. Here, we show that a chromatin remodeler, CHD4, a member of the Nucleosome Remodeling and Deacetylase (NuRD) complex, establishes chromatin states required for formation and maintenance of the ovarian reserve. Conditional loss of CHD4 in perinatal mouse oocytes results in acute death of NGOs and depletion of the ovarian reserve. CHD4 establishes closed chromatin at regulatory elements of pro-apoptotic genes to prevent cell death and at specific genes required for meiotic prophase I to facilitate the transition from meiotic prophase I oocytes to meiotically-arrested NGOs. In male germ cells, CHD4 establishes closed chromatin at the regulatory elements of pro-apoptotic genes, allowing germ cell survival. These results demonstrate a role for CHD4 in defining a chromatin state that ensures germ cell survival, thereby enabling the long-term maintenance of both female and male germ cells.
    DOI:  https://doi.org/10.1093/nar/gkaf008
  8. bioRxiv. 2025 Jan 24. pii: 2025.01.23.634177. [Epub ahead of print]
    Nucleoporins shape germ granule architecture and balance small RNA silencing pathways.
    Kun Shi, Ying Zhang, Zhenzhen Du, Symonne C Liu, Xinyu Fan, Heng-Chi Lee, Donglei Zhang.
      Animals have evolved distinct small RNA pathways, including piRNA and siRNA, to silence invasive and selfish nucleic acids. piRNA pathway factors are concentrated in perinuclear germ granules that frequently associate with nuclear pore complexes (NPCs). However, the factors mediating germ granule-NPC association and the functional relevance of such association remain unknown. Here we show that the conserved nucleoporins NPP-14 (NUP-214) and NPP-24 (NUP-88), components of the cytoplasmic filaments of NPC, play critical roles in anchoring germ granule to NPC and in attenuating piRNA silencing In C. elegans . Proximity labeling experiments further identified EPS-1 (enhanced piRNA silencing) as a key germ granule factor contributing to germ granule-NPC interaction. In npp-14 , npp-24, or eps-1 mutant animals, we observed fewer but enlarged, unorganized germ granules, accompanied by the over-amplification of secondary small RNAs at piRNA targeting sites. Nonetheless, we found this enhancement of piRNA silencing comes at the cost of dampened RNAi efficiency and RNAi inheritance. Together, our studies uncovered factors contributing to germ granule-NPC association and underscored the importance of spatial organization of germ granules in balancing small RNA silencing pathways.
    DOI:  https://doi.org/10.1101/2025.01.23.634177
  9. RNA Biol. 2025 Dec;22(1): 1-11
    Germ granule-mediated mRNA storage and translational control.
    Hoang-Anh Pham-Bui, Mihye Lee.
      Germ cells depend on specialized post-transcriptional regulation for proper development and function, much of which is mediated by dynamic RNA granules. These membrane-less organelles form through the condensation of RNA and proteins, governed by multivalent biomolecular interactions. RNA granules compartmentalize cellular components, selectively enriching specific factors and modulating biochemical reactions. Over recent decades, various types of RNA granules have been identified in germ cells across species, with extensive studies uncovering their molecular roles and developmental significance. This review explores the mRNA regulatory mechanisms mediated by RNA granules in germ cells. We discuss the distinct spatial organization of specific granule components and the variations in material states of germ granules, which contribute to the regulation of mRNA storage and translation. Additionally, we highlight emerging research on how changes in these material states, during developmental stages, reflect the dynamic nature of germ granules and their critical role in development.
    Keywords:  RNA granule; germ cells; mRNA storage; phase separation; post-transcriptional regulation; translational control
    DOI:  https://doi.org/10.1080/15476286.2025.2462276
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