bims-cebooc Biomed News
on Cell biology of oocytes
Issue of 2025–11–02
thirteen papers selected by
Gabriele Zaffagnini, Universität zu Köln
  1. Surface mechanics and compressive stress impact mammalian follicle development.
  2. Maternal factor OTX2 regulates human embryonic genome activation and early development.
  3. Live-Cell Imaging of Chromosome Segregation During Mouse Oocyte Meiosis.
  4. Broad H3K4me3 domains support oocyte genome silencing and maturation but are dispensable for repression in early embryos.
  5. Oocyte checkpoint response to the spindle poison depends on the cytoplasm volume.
  6. Cytoplasmic movement velocity in unfertilized mouse oocytes: a supportive but not definitive marker of embryo quality.
  7. mTORC1-dependent suppression of autophagic activity in somatic cell nuclear transfer mouse embryos.
  8. FGF receptor 2 signaling in granulosa cells is required for normal female fertility in mice.
  9. DILP8 serves as a mature follicle sensor to prevent excessive accumulation of mature follicles in Drosophila ovaries and oocyte aging.
  10. In vivo differentiation of embryonic cells devoid of key reprogramming factors.
  11. In vitro approaches to study centriole and cilium function in early mouse embryogenesis.
  12. Protocol for lattice light-sheet time-lapse imaging of early post-implantation mouse embryos.
  13. TET knockout cells transit between pluripotent states and exhibit precocious germline entry.
  1. Nat Commun. 2025 Oct 31. 16(1): 9578
    Surface mechanics and compressive stress impact mammalian follicle development.
    Arikta Biswas, Yuting Lou, Boon Heng Ng, Kosei Tomida, Sukhada Darpe, Kim Whye Leong, Zihao Wu, Thong Beng Lu, Xiang Teng, Yusuke Toyama, Isabelle Bonne, Chii Jou Chan.
      The maturation of functional eggs in ovaries is essential for successful reproduction in mammals. Despite its biological and clinical importance, the underlying mechanisms regulating folliculogenesis remain enigmatic. Here, using murine ovaries, we report that the theca cells surrounding secondary follicles play a critical role in regulating follicle development through mechanical signalling. Using biophysical approaches, we found that the contractile theca cells exert significant compressive stress to the follicular interior through active assembly of fibronectin. Manipulation of compressive stress by targeting theca cell contractility, basement membrane integrity or intrafollicular pressure leads to changes in follicle size and mechanics, granulosa cell YAP signalling and oocyte-granulosa cell communications. Transcriptomics and quantitative immunofluorescence reveal that compressive stress impacts functional follicle growth through regulating the balance between granulosa cell proliferation and death that drives tissue pressure homeostasis. Altogether, our study uncovers unique mechanical functions of theca cells and provides quantitative evidence of the role of compressive stress in regulating mammalian folliculogenesis.
    DOI:  https://doi.org/10.1038/s41467-025-65390-y
  2. Nat Genet. 2025 Oct 27.
    Maternal factor OTX2 regulates human embryonic genome activation and early development.
    Qiuyan Wang, Chuanxin Zhang, Yanna Dang, Jiaqi Sun, Zhuoning Zou, Cheng Li, Shuiying Ma, Zongyu Li, Hui Liu, Xiaonan Ma, Zhen Yang, Lijuan Wang, Keliang Wu, Zi-Jiang Chen, Wei Xie, Han Zhao.
      Transcription factors (TFs) are instrumental in kickstarting embryonic genome activation (EGA) in many species, yet their regulatory roles in human embryos remain poorly understood. Here, we show that OTX2, a maternally provided PRD-like homeobox TF, is required for proper human EGA and early development. At the four-cell stage, OTX2 promotes activation of key EGA genes, including TPRX1 and TPRX2, and the EGA-associated repeat HERVL-int and MLT2A1. At EGA targets, OTX2 directly binds promoters and putative enhancers, many of which overlap with Alu and MaLR repetitive elements containing the OTX2 motif, and promotes chromatin accessibility. The transcriptome and developmental defects upon OTX2 knockdown are partially rescued by overexpression of TPRX1 and TPRX2. Finally, joint knockdown of OTX2 and TPRXL, encoding another maternal PRD-like homeobox TF, exacerbates chromatin opening and EGA defects at the 8C stage. These findings establish OTX2 as a crucial maternal TF that awakes the genome at the beginning of human life.
    DOI:  https://doi.org/10.1038/s41588-025-02350-8
  3. J Vis Exp. 2025 Oct 10.
    Live-Cell Imaging of Chromosome Segregation During Mouse Oocyte Meiosis.
    Chenxi Zhou, Hayden A Homer.
      Accurate chromosome segregation during oocyte meiosis is essential for ensuring proper embryonic development and preventing aneuploidy-related disorders. Live-cell imaging combined with fluorescence labelling techniques have become a powerful approach for studying meiotic chromosome dynamics with high spatiotemporal resolution. In this protocol, we summarize key methodologies for visualizing chromosome segregation in live mouse oocytes, focusing on the use of histone H2B-RFP for chromatin labelling and SiR-Tubulin for spindle tracking. We describe the procedures for sample preparation, mRNA microinjection, oocyte culture, live-cell imaging chamber setup, and confocal microscopy settings, all optimized to achieve high-resolution imaging while minimizing phototoxicity. Furthermore, we highlight critical experimental considerations such as phototoxicity, image processing, and quantitative analysis of meiotic events. By providing a comprehensive evaluation of current methodologies, this protocol serves as a practical guide for researchers seeking to investigate chromosome dynamics in live oocytes and improve the accuracy and reproducibility of meiotic studies.
    DOI:  https://doi.org/10.3791/68847
  4. Development. 2025 Nov 01. pii: dev204638. [Epub ahead of print]152(21):
    Broad H3K4me3 domains support oocyte genome silencing and maturation but are dispensable for repression in early embryos.
    Trine Skuland, Madeleine Fosslie, Sherif Khodeer, Endalkachew Ashenafi Alemu, Jens Vilstrup Johansen, Marie Indahl, Blanca Corral Castroviejo, Yanjiao Li, Mads Lerdrup, John Arne Dahl, Peter Zoltan Fedorcsak, Gareth D Greggains.
      Epigenetic reprogramming and embryonic genome activation (EGA) are crucial events during early development. Establishment of distinctive broad histone H3 lysine 4 trimethylation (H3K4me3) domains in the oocyte is necessary for genome silencing, and their removal in the 2-cell embryo is crucial for EGA and development in mice. However, the stage-specific requirement for broad H3K4me3 domains is unclear. Here, we show that inducing broad H3K4me3 removal in mouse oocytes can relieve genome silencing, impair oocyte maturation timing, and may cause transcriptional reactivation in resulting parthenogenetic 1-cell embryos. We further demonstrate that broad H3K4me3 demethylation precedes EGA but, surprisingly, premature depletion in zygotes or early 2-cell embryos does not alter the transcriptional program. Our findings suggest that broad H3K4me3 domains are required for oocyte genome silencing, timely maturation and post-fertilisation silencing, but onward pre-EGA transcriptional repression is not dependent on the original mark. This work contributes to the understanding of events and mechanisms involved in genome silencing and activation in early development, providing insight into potential modes of failure that may contribute to infertility.
    Keywords:  Activation; Embryo; H3K4me3; KDM5B; Oocyte; Silencing
    DOI:  https://doi.org/10.1242/dev.204638
  5. Syst Biol Reprod Med. 2025 Dec;71(1): 538-548
    Oocyte checkpoint response to the spindle poison depends on the cytoplasm volume.
    Regina Daszkiewicz, Łukasz Gąsior, Katarzyna Kotarska, Zbigniew Polanski.
      The embryonic aneuploidy in mammals may arise from impaired Spindle Assembly Checkpoint (SAC) function, a mechanism which prevents errors in chromosome segregation by blocking anaphase in response to spindle anomalies. Mammalian oocytes are particularly susceptible to these errors, possibly because the large oocyte volume favors dilution of the checkpoint signal, preventing its efficient function. This study aimed to investigate hypothesis that oocyte cytoplasmic volume affects SAC functionality. Oocyte size was manipulated in prophase oocytes (before nuclear envelope breakdown, NEBD) or in M-phase oocytes (after NEBD) by either reducing or increasing cytoplasmic volume by half. These oocytes were then cultured in the presence of nocodazole which activated the SAC by arresting oocytes in metaphase I of the first meiotic division. The functionality of SAC was assessed by measuring the proportion of oocytes escaping SAC-induced metaphase I arrest and completing the first meiotic division i.e., extruding the first polar body and entering the metaphase II of the second meiotic division. Reduction of the cytoplasmic volume in the prophase stage resulted in stronger checkpoint function, with only 4% of oocytes escaping SAC arrest compared to 36% of control normal-sized oocytes. Conversely, enlarged oocytes showed diminished checkpoint efficiency, with 54% bypassing checkpoint-induced arrest compared to 20% of control normal-sized oocytes. Importantly, no such relationship was observed when cytoplasmic volume was altered in oocytes after NEBD. This may suggest that the SAC depends on some nucleus-associated factors that are released into the cytoplasm after NEBD, since such factors would be twice as concentrated in oocytes undergoing volume reduction before NEBD compared to those undergoing reduction after NEBD. These results prove that SAC efficiency in mouse oocytes is influenced by cytoplasmic volume, with larger volumes impairing its function.
    Keywords:  Spindle Assembly Checkpoint; aneuploidy; mouse female meiosis; nocodazole; nuclear factors; oocyte size
    DOI:  https://doi.org/10.1080/19396368.2025.2576084
  6. Theriogenology. 2025 Oct 25. pii: S0093-691X(25)00451-0. [Epub ahead of print]251 117725
    Cytoplasmic movement velocity in unfertilized mouse oocytes: a supportive but not definitive marker of embryo quality.
    Monika Fluks, Alicja Rak, Anna Ajduk.
      In vitro fertilization (IVF) is an essential method not only in the treatment of infertility but also in livestock breeding and in the management of zoo populations and endangered species. The success of IVF depends on oocyte quality, necessitating reliable methods for assessing female gamete competence. Here, we investigated biomechanical properties - particularly cytoplasmic movement velocity (CMV), known to be dependent on cytoskeletal functionality - as noninvasive markers of oocyte quality. We used mouse immature (GV) and mature (MII) oocytes as an experimental model. Cortical tension and cellular stiffness were measured using micropipette aspiration, and CMV was assessed with time-lapse imaging combined with Particle Image Velocimetry analysis. Our data indicate that transcriptionally quiescent GV oocytes (SN) exhibit higher CMV than transcriptionally active GV oocytes (NSN). Moreover, maternal and postovulatory aging, cryopreservation, and in vitro maturation significantly affect the CMV of MII oocytes. However, CMV in freshly ovulated MII oocytes does not correlate with their ability to develop to the blastocyst stage. We also show that changes in CMV are typically accompanied by opposite changes in cellular stiffness, with one exception - the transition from GV to MII stage, during which both CMV and stiffness decrease. Our results suggest that CMV may facilitate oocyte quality assessment, particularly in immature oocytes, by supporting the selection of SN-type oocytes. However, CMV measured in MII oocytes alone is not sufficient to predict quality of the resulting embryo. Further research is needed to validate these findings in target species and to optimize relevant IVF protocols.
    Keywords:  Cortical tension; Cytoplasmic movement velocity; Developmental potential; Oocyte; Quality assessment; Stiffness
    DOI:  https://doi.org/10.1016/j.theriogenology.2025.117725
  7. Reproduction. 2025 Dec 01. pii: e250338. [Epub ahead of print]170(6):
    mTORC1-dependent suppression of autophagic activity in somatic cell nuclear transfer mouse embryos.
    Takaki Tatebe, Dinh Quoc Pham, Atsuo Ogura, Kimiko Inoue.
       In brief: The non-genomic factors responsible for developmental arrest in SCNT embryos remain poorly understood. Using live-cell fluorescence imaging, we revealed that autophagic activity is impaired in preimplantation SCNT embryos, possibly due to ectopic activation of the mTORC1 signaling pathway, providing new insights into cytoplasmic barriers to cloning efficiency.
    Abstract: Activation of autophagy after fertilization is essential for mammalian embryonic development, as it supplies embryos with nutrients and energy. Somatic cell nuclear transfer (SCNT) embryos frequently exhibit developmental arrest, largely because of incomplete genomic reprogramming; however, the role of non-genomic factors remains unclear. Here, we investigated autophagy dynamics in mouse SCNT embryos using immunostaining and live-cell fluorescence imaging. In fertilized embryos, autophagy increased markedly from the late 2-cell stage and peaked at the morula stage. SCNT embryos followed a similar timeline but consistently showed reduced autophagic activity. Notably, the autophagic activity levels varied among SCNT embryos and positively correlated with their developmental potential. Attempts to enhance genomic reprogramming, including the removal of somatic histone methylation, did not restore autophagy. Instead, transcriptome analysis revealed ectopic activation of mTORC1 signaling as a likely cause of impaired autophagy. Consistently, treatment with an mTORC1 inhibitor successfully rescued autophagic activity in SCNT embryos. These findings identify a persistent autophagy defect during preimplantation development in SCNT embryos and suggest that modulation of non-genomic pathways, such as mTORC1 signaling, could improve SCNT efficiency.
    Keywords:  autophagy; mTORC1; preimplantation embryo; somatic cell nuclear transfer
    DOI:  https://doi.org/10.1530/REP-25-0338
  8. Reproduction. 2025 Dec 01. pii: e250219. [Epub ahead of print]170(6):
    FGF receptor 2 signaling in granulosa cells is required for normal female fertility in mice.
    Takuya Kanke, Ayaka Ichikawa, Yuki Akimoto, Shunichi Matsunaga, Wataru Fujii, Tsutomu Endo, Kunihiko Naito, Koji Sugiura.
       In brief: Fibroblast growth factor (FGF) signaling has been implicated in ovarian follicular development in mammals, but its in vivo role in female fertility remains unclear. This study reveals the requirement of fibroblast growth factor receptor 2 (FGFR2) signaling in ovarian granulosa cells for normal female fertility in mice, likely by regulating glycolysis in cumulus cells and enhancing oocyte developmental competence.
    Abstract: FGF signaling has been implicated in ovarian follicular development in mammals, but its in vivo role in female fertility remains unclear. To investigate this role, we generated granulosa cell-specific conditional knockout (cKO) mice lacking FGF receptor 2 (FGFR2). Fgfr2 cKO female mice exhibited significantly reduced fertility despite normal follicular development, estrous cycles, and ovulation. In contrast, cumulus cells in cKO mice showed decreased expression of glycolytic enzymes such as PFKP and LDHA, potentially impairing metabolic support for oocytes. Consequently, cKO cumulus cells were less competent than control cells in supporting the meiotic resumption of oocytes under in vitro conditions. Furthermore, while cKO oocytes developed into blastocysts at normal rates in vitro, their ability to reach term after embryo transfer was significantly diminished. These findings demonstrate that FGFR2-mediated FGF signaling in granulosa cells is essential for normal female fertility, likely by regulating glycolysis in cumulus cells and promoting oocyte developmental competence.
    Keywords:  fibroblast growth factor; glycolysis; granulosa cells; ovary
    DOI:  https://doi.org/10.1530/REP-25-0219
  9. Development. 2025 Oct 31. pii: dev.204827. [Epub ahead of print]
    DILP8 serves as a mature follicle sensor to prevent excessive accumulation of mature follicles in Drosophila ovaries and oocyte aging.
    Rebecca Oramas, Katarina Yacuk, Stella E Cho, Natalie R Aloisio, Jianjun Sun.
      Excessive mature follicle accumulation in ovaries harms oocyte health and offspring viability. The mechanism by which females count mature follicles in their ovaries remains a mystery. Recent work demonstrated that Drosophila insulin-like peptide 8 (DILP8) is expressed in mature follicle cells but not in younger follicles. Here, we found that DILP8 is not essential for mating-induced ovulation but plays critical role in inducing ovulation in virgin females and preventing excessive accumulation of mature follicles. Excessive accumulation of mature follicles in dilp8-knockdown females leads to poor oocyte quality. In addition, knockdown of Lgr3 (Leucine-rich repeat-containing G protein-coupled receptor 3), encoding a previously identified DILP8 receptor, globally or neuronally showed similar ovulation/egg laying defects, accumulation of mature follicles, and poor oocyte quality in virgin females. Therefore, DILP8 functions as a mature follicle sensor to prevent excessive accumulation of mature follicles and maintain oocyte quality likely through neuronal Lgr3 receptor in virgin females. Our findings suggest that DILP8/Lgr3 is likely critical for maintaining the optimal reproductive fitness of virgin females and for species survival in the wild, where mating success is not guaranteed.
    Keywords:   dilp8 ; lgr3 ; Mature follicle sensor; Oocyte aging; Virgin ovulation
    DOI:  https://doi.org/10.1242/dev.204827
  10. Cell Rep. 2025 Oct 30. pii: S2211-1247(25)01269-0. [Epub ahead of print]44(11): 116498
    In vivo differentiation of embryonic cells devoid of key reprogramming factors.
    Scott E Youlten, Liyun Miao, Caroline Hoppe, Curtis W Boswell, Damir Musaev, Mario Abdelmessih, Damilola Olowookere, Linnea A Weiss, Smita Krishnaswamy, Antonio J Giraldez, Valerie A Tornini.
      Embryonic cell differentiation depends on reprogramming of the oocyte and sperm nucleus into a transient totipotent state. In zebrafish, this coincides with genome activation, which is regulated by the pioneer factors Nanog, Pou5f3, and Sox19b (NPS). Here, we investigate the role of NPS in developmental reprogramming and differentiation by analyzing the fate of NPS mutant cells in a wild-type embryo using single-cell RNA-seq. We find that many cells fail to activate transcription or undergo cell death, while others acquire gene expression profiles that resemble germ cells, neural progenitors, and motoneuron states. These cells achieve intermediate transcriptional states, revealing the essential role of NPS in coordinating nuclear and cytoplasmic reprogramming and preventing the premature activation of lineage-specific differentiation programs. These results demonstrate that most developmental programs require developmental reprogramming by NPS, yet some cells can bypass transient totipotency to achieve intermediate developmental states resembling wild-type states in vivo.
    Keywords:  CP: Developmental biology; cell identity; cell states; development; differentiation; pluripotency factors; reprogramming; single-cell transcriptomics
    DOI:  https://doi.org/10.1016/j.celrep.2025.116498
  11. Life Sci Alliance. 2026 Jan;pii: e202503358. [Epub ahead of print]9(1):
    In vitro approaches to study centriole and cilium function in early mouse embryogenesis.
    Isabella Voelkl, Tamara Civetta, Mirijam Egg, Marie Huber, Songjie Feng, Alexander Dammermann, Christa Buecker.
      Although centrioles and primary cilia play an essential role in early mammalian development, their specific function during the interval between their initial formation and the subsequent arrest of embryogenesis in embryos deficient in centrioles or cilia remains largely unexplored. Here, we demonstrate that different 3D in vitro model systems recapitulate early centriole and cilium formation in mouse development. Centrioles and cilia are dispensable in 3D in vitro mouse rosettes, a model system that mimics key events of implantation, including polarization and lumenogenesis. In gastruloids, a model system that recapitulates developmental processes up to E8.5, centriole loss results in early disassembly that can be rescued by additional p53 deletion. In contrast, cells devoid of cilia continue to form elongated, differentiated and polarized gastruloids, with minor differences at 96 h. Finally, we show that in a mutant affecting the centriolar distal appendages, cilia are absent from 2D cultures, but are capable of forming in 3D rosettes and gastruloids, highlighting the importance of multifactorial 3D environment setups in developmental studies.
    DOI:  https://doi.org/10.26508/lsa.202503358
  12. STAR Protoc. 2025 Oct 23. pii: S2666-1667(25)00559-3. [Epub ahead of print]6(4): 104153
    Protocol for lattice light-sheet time-lapse imaging of early post-implantation mouse embryos.
    Shifaan Thowfeequ, Helena Coker, Marco Fritzsche, Shankar Srinivas.
      Lattice light-sheet microscopy offers unprecedented spatial and temporal resolution for visualizing morphogenetic and physiological processes, while minimizing photodamage. Here, we present a detailed protocol for time-lapse imaging of post-implantation mouse embryos, using lattice light-sheet microscopy. We describe steps for embryo isolation, mounting and culture, setting up of imaging parameters, and pipelines for processing the data generated in preparation for downstream analyses. This approach is also suitable for stem cell-derived embryo models, organoids, and small organ explants. For complete details on the use and execution of this protocol, please refer to Thowfeequ et al.1 and Stower et al.2.
    Keywords:  Developmental biology; Microscopy; Organoids
    DOI:  https://doi.org/10.1016/j.xpro.2025.104153
  13. EMBO J. 2025 Oct 27.
    TET knockout cells transit between pluripotent states and exhibit precocious germline entry.
    Raphaël Pantier, Elisa Barbieri, Sara Gonzalez Brito, Ella Thomson, Tülin Tatar, Douglas Colby, Man Zhang, Ian Chambers.
      TET1, TET2 and TET3 are DNA demethylases with important roles in development and differentiation. To assess the contributions of TET proteins to cell function during early development, single and compound knockouts of Tet genes in mouse pluripotent embryonic stem cells (ESCs) were generated. Here, we show that TET proteins are not required to transit between naïve, formative and primed pluripotency states. Moreover, ESCs with double knockouts of Tet1 and Tet2 or triple knockouts of Tet1, Tet2 and Tet3 are phenotypically indistinguishable. TET1,2,3-deficient ESCs exhibit differentiation defects and fail to activate somatic gene expression, retaining expression of pluripotency transcription factors. Therefore, TET1 and TET2, but not TET3 act redundantly to facilitate somatic differentiation. Importantly however, TET-deficient ESCs can differentiate into primordial germ cell-like cells (PGCLCs), and do so at high efficiency in the presence or absence of PGC-promoting cytokines. Moreover, acquisition of a PGCLC transcriptional programme occurs more rapidly in TET-deficient cells. These results establish that TET proteins act at the juncture between somatic and germline fates: without TET proteins, epiblast cell differentiation defaults to the germline.
    Keywords:  Differentiation; Pluripotency; Primordial Germ Cells; Stem Cells; TET Proteins
    DOI:  https://doi.org/10.1038/s44318-025-00597-9
This page is being maintained by Thomas Krichel. It was last updated on 2025‒11‒02 at 8:34.