bims-cebooc 2025-09-07 papers

bims-cebooc

Biomed News

on Cell biology of oocytes

Issue of 2025–09–07
seventeen papers selected by
Gabriele Zaffagnini, Universität zu Köln

Preventing CpG hypermethylation in oocytes safeguards mouse development.
Translational repression by 4E-T is crucial to maintain the prophase-I arrest in vertebrate oocytes.
Farnesylation-Dependent Kinetochore Targeting of CENP-F Is Essential for Oocyte Meiotic Progression and Female Fertility.
RNA binding protein SERBP1 is indispensable for oocyte development and maturation in mice.
Oocyte polarity is established independently of the Balbiani body.
Replication competition drives the selective mtDNA inheritance in Drosophila ovary.
HEIP1 orchestrates pro-crossover protein activity during mammalian meiosis.
Biophysical, cellular, and mouse model approaches to investigate the mechanical regulation of folliculogenesis.
A persistent intracellular bridge and cell cycle misregulation enable polar body cell divisions and tumor formation in Mos -deficient eggs.
Effects of reversine and proTAME treatment on chromosome segregation during mouse oocyte maturation.
Controlling intermolecular base pairing in Drosophila germ granules by mRNA folding and its implications in fly development.
Distinct cellular and reproductive consequences of meiotic chromosome synapsis defects in syce2 and sycp1 mutant zebrafish.
Long-term mitochondria-endoplasmic reticulum complexes in the oocytes and early embryos of a matrotrophic pseudoscorpion Chelifer cancroides.
Loss of Nuclear Protein Dyro Causes Abnormalities in Nurse Cell Nuclei and Abort Oogenesis at Mid-Oogenesis Checkpoint.
The impact of maternal diet-induced obesity on offspring primordial oocyte mitochondria at birth and at weaning.
Adipocyte-Derived Amino Acid Storage Proteins are Required for Germline Stem Cell Maintenance in Adult Drosophila Females.
Imaging Transzonal Projections in the Cumulus-Oocyte Complexes: challenges and solutions†.

Dev Cell. 2025 Aug 29. pii: S1534-5807(25)00505-2. [Epub ahead of print]

Preventing CpG hypermethylation in oocytes safeguards mouse development.

Yumiko K Kawamura, Evgeniy A Ozonov, Panagiotis Papasaikas, Takashi Kondo, Nhuong V Nguyen, Michael B Stadler, Sebastien A Smallwood, Haruhiko Koseki, Antoine H F M Peters.

  Except for regulatory CpG-island sequences, genomes of most mammalian cells are widely DNA-methylated. In oocytes, though, DNA methylation (DNAme) is largely confined to transcribed regions. The mechanisms restricting de novo DNAme in oocytes and their relevance thereof for zygotic genome activation and embryonic development are largely unknown. Here we show that KDM2A and KDM2B, two histone demethylases, prevent genome-wide accumulation of histone H3 lysine 36 di-methylation, thereby impeding DNMT3A-catalyzed DNAme. We demonstrate that aberrant DNAme at CpG islands inherited from Kdm2a/Kdm2b double-mutant oocytes represses gene transcription in two-cell embryos. Aberrant maternal DNAme impairs pre-implantation embryonic development, which is suppressed by Dnmt3a deficiency during oogenesis. Hence, KDM2A/KDM2B are essential for confining the oocyte methylome, thereby conferring competence for early embryonic development. Our research implies that the reprogramming capacity eminent to early embryos is insufficient for erasing aberrant DNAme from maternal chromatin, and that early development is susceptible to gene dosage haplo-insufficiency effects.

Keywords:  CpG island; DNA methylation; KDM2A; KDM2B; PRC1; Polycomb; embryogenesis; maternal epigenetic inheritance; oocyte; reprogramming

DOI:  https://doi.org/10.1016/j.devcel.2025.08.005
Nat Commun. 2025 Aug 28. 16(1): 8051

Translational repression by 4E-T is crucial to maintain the prophase-I arrest in vertebrate oocytes.

Andreas Heim, Shiya Cheng, Jan Orth, Florian Stengel, Melina Schuh, Thomas U Mayer.

Meiotic maturation of vertebrate oocytes occurs in the near-absence of transcription. Thus, female fertility relies on timely translational activation of maternal transcripts stockpiled in full-grown prophase-I-arrested oocytes. However, how expression of these mRNAs is suppressed to maintain the long-lasting prophase-I arrest remains mysterious. Utilizing fast-acting TRIM-Away, we demonstrate that acute loss of the translation repressor 4E-T triggers spontaneous release from prophase-I arrest in mouse and frog oocytes. This is due to untimely expression of key meiotic drivers like c-Mos and cyclin-B1. Notably, mutant 4E-T associated with premature ovarian insufficiency in women fails to maintain the prophase-I arrest in Xenopus oocytes. We further show that 4E-T association with eIF4E and PATL2 is critical for target mRNA binding and repression. Thus, 4E-T is a central factor in translational repression of mRNAs stockpiled in full-grown oocytes for later activation and, therefore, essential to sustain the oocyte pool throughout the reproductive lifespan of female vertebrates.

DOI: https://doi.org/10.1038/s41467-025-62971-9
Am J Obstet Gynecol. 2025 Aug 28. pii: S0002-9378(25)00588-5. [Epub ahead of print]

Farnesylation-Dependent Kinetochore Targeting of CENP-F Is Essential for Oocyte Meiotic Progression and Female Fertility.

Ou Zhong, Congjing Wang, Junqiang Zhang, Xiaolan Zhang, Ximan Rui, Qiqi Cao, Xinru Jia, Pinhua Wang, Jie Ding, Xiufeng Ling, Hong Li, Qingxia Meng, Chun Zhao, Ran Huo.

   BACKGROUND: During mammalian oocyte meiosis, accurate chromosome segregation critically depends on precise regulation of kinetochore-microtubule (K-MT) attachments, a process monitored by the spindle assembly checkpoint (SAC). While CENP-F has been well characterized as a kinetochore-associated protein that stabilizes K-MT connections during mitosis, its functional mechanisms during meiosis remain poorly understood. In particular, there is still controversy over whether farnesylation modification governs localization and functionality of CENP-F. Concurrently, clinical investigations face a knowledge gap regarding the genetic basis of oocyte maturation arrest, a prevalent phenotype observed in female infertility patients.
OBJECTIVE: This study aims to reveal the regulatory mechanism of CENP-F farnesylation modification on its meiotic function and explore the association between CENP-F gene mutations and female oocyte maturation disorders.
STUDY DESIGN: Previous studies have shown that CENP-F is essential for chromosome segregation during mitosis, but its functional mechanism during meiosis remains poorly understood. Oocyte microinjection, western blotting, co-immunoprecipitation (Co-IP), and immunofluorescence were used to explore the localization and function of CENP-F in oocytes. The role of CENP-F farnesylation in mouse oocytes was investigated using pharmacological (farnesyltransferase inhibitor treatment) and genetic (C3111S point mutation) methods. Subsequently, four patients with CENP-F mutations were identified in the whole-exome sequencing (WES) dataset consisting of 179 infertile patients with oocyte maturation disorders. Mouse oocyte and 293T cell models were used to verify the mechanism of patient-derived CENP-F mutations causing oocyte maturation disorders.
RESULTS: Microinjection of Cenp-f siRNA into mouse oocytes significantly reduced maturation rates (77.84±2.087% vs 34.26±4.748%, P<.01), with the majority arrested at metaphase I (MI) (17.69±2.207% vs 44.93±5.539%, P<.05). Time-course immunofluorescence analysis revealed dynamic CENP-F localization: initially dispersed across chromosome following nuclear envelope breakdown (NEBD), then progressively accumulating at kinetochores by MI. Co-IP assays confirmed a direct interaction between CENP-F and AURKB. Knockdown of AURKB would damage the kinetochore localization of CENP-F in oocytes. Farnesylation inhibition (via farnesyltransferase inhibitor or C3111S mutation) significantly decreased oocyte maturation rates (75.58±3.703% vs 46.18±1.282%, P<.01; 75.58±3.703% vs 44.04±2.541%, P<.01), concomitantly weakening interaction between CENP-F and AURKB (P<.01) and disrupting kinetochore localization. Genetic screening identified four CENP-F mutations in 179 infertile women with oocyte maturation arrest. Microinjection of patient-derived mutant CENP-F cRNAs into mouse oocytes significantly reduced maturation rates (77.00±2.411% vs 49.10±6.561%, P<.01; 77.00±2.411% vs35.43±1.035%, P<.01; 77.00±2.411% vs 55.43±1.288%, P<.05; 77.00±2.411% vs 40.00±4.187%, P<.01). Two of these mutations (K1708T/S1971fs) can reduce the farnesylation of CENP-F (P<.05/P<.01), damage its interaction with AURKB (P<0.05/P<0.01), and disrupt the kinetochore localization. Both CENP-F depletion and patient mutations induced constitutive SAC activation, and the treatment with SAC inhibitor partially rescued the meiotic arrest phenotype in oocytes (P<.05).
CONCLUSION: This study represents the first demonstration of a direct association between CENP-F genetic defects and human infertility, uncovering a novel farnesylation-dependent mechanism that governs meiotic progression, while simultaneously identifying CENP-F as a potential molecular marker for diagnosing oocyte maturation failure.

Keywords:  CENP-F; Farnesylation; Female infertility; Kinetochore; Oocyte metaphase I arrest; Spindle assembly checkpoint

DOI:  https://doi.org/10.1016/j.ajog.2025.08.031
Mol Cell Endocrinol. 2025 Sep 01. pii: S0303-7207(25)00195-9. [Epub ahead of print] 112644

RNA binding protein SERBP1 is indispensable for oocyte development and maturation in mice.

Lingjuan Wang, Sijin OuYang, Bin Li, Na Kong.

  RNA-binding proteins (RBPs) are critical regulators of post-transcriptional gene expression and RNA processing during mammalian oocyte development. SERPINE1 mRNA-binding protein 1 (SERBP1), a conserved RNA-binding protein (RBP), exhibits prominent expression in the female reproductive system and throughout oogenesis. Conditional deletion of Serbp1 using oocyte-specific Zp3⁠/⁠Gdf9⁠-Cre drivers resulted in arrested oocyte growth, female infertility, and failure of blastocyst formation from two-cell embryos. Phenotypic analysis revealed spindle assembly defects, impaired asymmetric division, and compromised meiotic competence in oocytes. Notably, Serbp1 ablation also induced granulosa cell apoptosis and elevated Erk1/2 phosphorylation levels, indicating dysregulation of somatic microenvironment. Furthermore, conditional knockout mice exhibited prolonged diestrus cycles. Collectively, these findings demonstrate that SERBP1 coordinates essential RNA-regulatory functions for oocyte developmental competence through both cell-autonomous mechanisms and somatic-germline crosstalk.

Keywords:  Folliculogenesis; Oocyte maturation; SERBP1; infertility

DOI:  https://doi.org/10.1016/j.mce.2025.112644
bioRxiv. 2025 Aug 27. pii: 2025.08.26.672409. [Epub ahead of print]

Oocyte polarity is established independently of the Balbiani body.

Manami Kobayashi, Joseph Zinski, Mary C Mullins.

In most animals, oocyte polarity establishes the embryonic body plan by asymmetrically localizing axis-determining transcripts. These transcripts first localize in Xenopus and zebrafish oocytes to the Balbiani body (Bb), a large membrane-less organelle conserved from insects to humans. The Bb is transient, disassembling and anchoring at one pole the axis-determining transcripts that establish the vegetal pole of the oocyte. Aggregation of the Bb depends on the Bucky ball (Buc) protein, an intrinsically disordered protein with a prion-like self-aggregation domain. In zebrafish buc null mutants, the Bb fails to form and oocytes lack polarity. Here, we established buc hypomorphic mutants that fail to form the Bb, but remarkably Buc protein and vegetal mRNAs localized normally at the vegetal cortex of the oocyte. Thus, these buc hypomorphic mutants displayed normal oocyte polarity, demonstrating that the Bb is not required to establish oocyte polarity. We found that both a reduced Buc protein level and truncation of the N-terminal 10 amino acids contribute to Bb failure in the hypomorphic mutants.

DOI: https://doi.org/10.1101/2025.08.26.672409
Cell Rep. 2025 Sep 04. pii: S2211-1247(25)00992-1. [Epub ahead of print]44(9): 116221

Replication competition drives the selective mtDNA inheritance in Drosophila ovary.

Cheng Zhang, Zhe Chen, Hansong Ma, Hong Xu.

  Purifying selection that limits the transmission of harmful mitochondrial DNA (mtDNA) mutations has been observed in both human and animal models. Yet, the precise mechanism underlying this process remains undefined. Here, we present a highly specific and efficient in situ imaging method capable of visualizing mtDNA variants that differ by only a few nucleotides at single-molecule resolution in Drosophila ovaries. Using this method, we revealed that selection primarily occurs within a narrow developmental window during germline cyst differentiation. At this stage, the proportion of the deleterious mtDNA variant decreases without a reduction in its absolute copy number. Instead, the healthier mtDNA variant replicates more frequently, thereby outcompeting the co-existing deleterious variant. These findings provide direct evidence that mtDNA selection is driven by replication competition rather than by active elimination processes, shedding light on a fundamental yet previously unresolved mechanism governing mitochondrial genome transmission.

Keywords:  CP: Molecular biology; germline; mitochondria; mitophagy; mtDNA inheritance; mtDNA mutation; mtDNA replication; oogenesis; purifying selection; rolling circle amplification; single-molecule imaging

DOI:  https://doi.org/10.1016/j.celrep.2025.116221
bioRxiv. 2025 Aug 28. pii: 2025.08.25.672081. [Epub ahead of print]

HEIP1 orchestrates pro-crossover protein activity during mammalian meiosis.

Arnaud De Muyt, Sunkyung Lee, Sushil Khanal, Laurine Dal Toe, Céline Adam, Raphael Mercier, Valérie Borde, Neil Hunter, Thomas Robert.

Meiotic crossovers are needed to produce genetically balanced gametes. In mammals, crossover formation is mediated by a conserved set of pro-crossover proteins via mechanisms that remain unclear. Here, we characterize a mammalian pro-crossover factor HEIP1. In mouse HEIP1 is essential for crossing over and fertility of both sexes. HEIP1 promotes crossing over by orchestrating the recruitment of other pro-crossover proteins, including the MutS γ complex (MSH4- MSH5) and E3 ligases (HEI10, RNF212, and RNF212B), that are required to mature crossover sites and recruit the crossover-specific resolution complex MutL γ . Moreover, HEIP1 directly interacts with HEI10, suggesting a direct role in controlling the recruitment of pro-crossover E3 ligases. During early stages of meiotic prophase I, HEIP1 interacts with the chromosome axes, independently of recombination, before relocalizing to the central region of the synaptonemal complex. We propose that HEIP1 is a new conserved master regulator of crossover proteins that controls different crossover maturation steps.
Significance Statement: Crossovers are essential to produce gametes by promoting the proper segregation of the homologous chromosomes. But, if misregulated, they can lead to genetic disorders, miscarriage and infertility. Their formation depends on the conserved pro-crossover factors, which repertoire is expanding and mode of action tightly regulated. This study highlights how the HEIP1 protein organizes pro-crossover protein activities in the mouse. Our findings show that HEIP1, by interacting early with chromosomes independently of recombination initiation, and orchestrating the recruitment of pro-crossover factors, including the MutSg complex and the RING proteins HEI10, RNF212 and RNF212B, is pivotal in this regulation. Our work is of significance to unravel crossover control during meiotic recombination, a conserved mechanism essential for gametes formation.

DOI: https://doi.org/10.1101/2025.08.25.672081
Semin Cell Dev Biol. 2025 Aug 30. pii: S1084-9521(25)00059-X. [Epub ahead of print]174 103649

Biophysical, cellular, and mouse model approaches to investigate the mechanical regulation of folliculogenesis.

Sara Pietroforte, Farners Amargant.

  Folliculogenesis, which is the process by which ovarian follicles develop to support oogenesis and hormone production, is essential for female fertility. Although hormonal and biochemical signaling pathways regulating folliculogenesis have been extensively studied, increasing evidence suggests that mechanical cues within the ovary also play a critical role. The ovary is composed of follicles, corpora lutea, and stroma, each contributing to a biomechanical microenvironment that might change across the reproductive lifespan. Additionally, the spatial organization of the ovary, with a collagen-rich cortex and a softer medulla, may influence follicle activation and growth. This review explores the hypothesis that mechanical properties of the ovary regulate folliculogenesis, integrating current knowledge on ovarian architecture, extracellular matrix composition, and mechanotransduction pathways. We highlight recent findings supporting mechanical regulation of folliculogenesis, discuss contradictory data, and describe the tools and models used to investigate this concept. By considering mechanical forces alongside hormonal and biochemical signals, we propose a more integrated view of the factors governing follicle development, with implications for understanding ovarian physiology and pathology.

Keywords:  Biomechanics; Folliculogenesis; Mechanotransduction; Oocyte quality; Ovary

DOI:  https://doi.org/10.1016/j.semcdb.2025.103649
bioRxiv. 2025 Aug 27. pii: 2025.08.26.672293. [Epub ahead of print]

A persistent intracellular bridge and cell cycle misregulation enable polar body cell divisions and tumor formation in Mos -deficient eggs.

Gisela Cairo, Muhammad A Haseeb, Karen Schindler, Soni Lacefield.

Mammalian female meiosis is uniquely regulated to produce a developmentally competent egg capable of supporting embryogenesis. During meiosis I, homologous chromosomes segregate, with half extruded into the first polar body. The egg then arrests at metaphase II and only resumes meiosis and extrudes the second polar body following fertilization. The MOS/MAPK signaling pathway is important for maintaining the metaphase II arrest; in mos -/- mutants, a subset of eggs undergo spontaneous parthenogenetic activation and exhibit additional abnormal cell divisions. To further understand the cell cycle mis-regulation in activated mos -/- eggs, we used time-lapse microscopy to monitor the abnormal divisions. We discovered that, following parthenogenetic activation, the first polar body can assemble a spindle, segregate chromosomes, and divide with timings similar to anaphase II onset in the egg. This behavior contrasts with wildtype polar bodies, which do not divide and are typically degenerated. We demonstrate that mos -/- eggs and polar bodies can exchange cytoplasm at the time of meiosis II spindle assembly, likely allowing the transfer of cell cycle regulators between the two compartments. Further inspection revealed that mos -/- eggs have defective meiotic midbody assembly with most eggs lacking a cap structure, which is needed to separate the two compartments. We report that polar bodies of mos -/- eggs can re-enter the cell cycle and undergo additional aberrant divisions. These findings identify MOS as a critical regulator of meiotic midbody formation and uncover a novel consequence of disrupted MOS/MAPK signaling: the potential for polar bodies to become mitotically active and contribute to tumor formation.

DOI: https://doi.org/10.1101/2025.08.26.672293
Zygote. 2025 Sep 01. 1-8

Effects of reversine and proTAME treatment on chromosome segregation during mouse oocyte maturation.

Shiina Yonekura, Chihiro Hasegawa, Shoma Ochi, Yoh Kinoshita, Jin Shibata, Mizuho Kobayashi, Hikari Ikema, Akifumi Nakata, Tomisato Miura, Hideaki Yamashiro.

  Aneuploidy in oocytes is a leading cause of implantation failure, miscarriage and congenital disorders. During meiosis, proper timing of chromosome segregation is regulated by the spindle assembly checkpoint (SAC) and the anaphase-promoting complex/cyclosome (APC/C). However, how pharmacological manipulation of these regulatory pathways affects aneuploidy remains incompletely understood. In this study, we investigated whether SAC inhibition by reversine induces aneuploidy in mouse oocytes and whether partial inhibition of APC/C by proTAME can alleviate these errors. Germinal vesicle (GV) oocytes were matured in vitro in the presence of various concentrations of reversine. To optimize the timing of treatment, oocytes were exposed to reversine for 0, 3, 5 or 7 h, followed by culture with or without proTAME. A proTAME-only group (2.5 nM) was also included. Chromosome spreads were analyzed at the metaphase II (MII) stage to determine aneuploidy rates. Reversine (5 nM) yielded an MII maturation rate of 80.5% but induced a high aneuploidy rate of 77.0%. Sequential treatment with 2.5 nM proTAME significantly reduced aneuploidy to 33.3%. In contrast, proTAME alone led to 79.0% aneuploidy, suggesting its effect is contingent upon prior SAC disruption. These results indicate that reversine compromises chromosomal integrity, while appropriately timed, low-dose proTAME can partially rescue segregation errors. Our findings underscore the potential of pharmacologically regulating APC/C activity to reduce aneuploidy and enhance oocyte quality, offering new avenues for improving outcomes in assisted reproductive technologies.

Keywords:  aneuploidy; chromosome segregation; meiosis; proTAME; reversine

DOI:  https://doi.org/10.1017/S0967199425100117
Nat Commun. 2025 Aug 30. 16(1): 8135

Controlling intermolecular base pairing in Drosophila germ granules by mRNA folding and its implications in fly development.

Siran Tian, Hung Nguyen, Ziqing Ye, Silvi Rouskin, D Thirumalai, Tatjana Trcek.

Drosophila germ granules are enriched with mRNAs critical for development. Within them, mRNAs cluster through intermolecular interactions that may involve base pairing. Here we apply in silico, in vitro and in vivo approaches to examine the type and prevalence of these interactions. We show that RNA clustering can occur without extended sequence complementarity (stretches of six or more continuous complementary bases) and that mRNAs display similar level of foldedness within germ granules as outside. Our simulations predict that clustering is driven by scattered, surface-exposed bases, enabling intermolecular base pairing. Notably, engineered germ granule mRNAs containing exposed GC-rich complementary sequences within stem loops located in the 3' untranslated region promote intermolecular interactions. However, these mRNAs are also expressed at lower levels, leading to developmental defects. Although germ granule mRNAs contain numerous GC-rich complementary sequences, RNA folding renders them inaccessible for intermolecular base pairing. We propose that RNA folding restricts intermolecular base pairing to maintain proper mRNA function within germ granules.

DOI: https://doi.org/10.1038/s41467-025-62973-7
PLoS Genet. 2025 Sep 05. 21(9): e1011656

Distinct cellular and reproductive consequences of meiotic chromosome synapsis defects in syce2 and sycp1 mutant zebrafish.

Iván Olaya, Ilara N Yilmaz, Naima Nour-Kasally, Ross E Charboneau, Bruce W Draper, Sean M Burgess.

The synaptonemal complex (SC) is a meiosis-specific structure that aligns homologous chromosomes and promotes the repair of meiotic DNA double-strand breaks (DSBs). To investigate how defects in SC formation affect gametogenesis in zebrafish, we analyzed mutations in two genes encoding core SC components: syce2 and sycp1. In syce2 mutants, chromosomes exhibit partial synapsis, primarily at sub-telomeric regions, whereas sycp1 mutant chromosomes display early prophase co-alignment but fail to synapse. Both mutants exhibit reduced efficiency in repairing meiotic DSBs compared to wild type. Despite these defects, syce2 and sycp1 mutant females are fertile. However, sycp1 mutant females produce a higher proportion of malformed progeny, correlating with increased univalent formation. While syce2 mutant males are fertile and produce normal offspring, sycp1 mutant males are sterile, with spermatocytes that transit prophase I but arrest at metaphase I or II. Additionally, sycp1 mutants display a male-biased sex ratio that can be suppressed by extending the developmental window for sex determination, suggesting that the absence of synapsis delays-but does not completely block- meiotic progression. Notably, embryos from syce2 and sycp1 mutant females exhibit widespread somatic mosaic aneuploidy, indicating that impaired meiotic chromosome dynamics can compromise genome stability during early development. In contrast to mouse SC mutants, the zebrafish syce2 and sycp1 mutants examined in this study progress through meiotic prophase I with minimal disruption, suggesting a less stringent surveillance mechanism for synapsis errors in zebrafish.

DOI: https://doi.org/10.1371/journal.pgen.1011656
Dev Biol. 2025 Aug 29. pii: S0012-1606(25)00237-4. [Epub ahead of print]527 318-330

Long-term mitochondria-endoplasmic reticulum complexes in the oocytes and early embryos of a matrotrophic pseudoscorpion Chelifer cancroides.

Izabela Jędrzejowska, Karol Małota, Arnold Garbiec.

  Mitochondria are considered key organelles for proper oocyte growth, maturation, fertilization, and embryo development. During oogenesis, they have been found to be highly dynamic organelles that interact with other cellular components. In this study, we analyzed the morphology and behavior of mitochondria in the oocytes and early embryos of the cosmopolitan pseudoscorpion Chelifer cancroides. Analyses were carried out using light, confocal, and transmission electron microscopy. Our results show that, in the early stages of oocyte growth, mitochondria gather close to the germinal vesicle within an organelle assemblage termed the Balbiani body (Bb). In the Bb, mitochondria increase in number and display a high membrane potential. In advanced previtellogenesis, when the Bb disperses, the mitochondria gradually populate the entire ooplasm and join the endoplasmic reticulum to form mitochondria-endoplasmic reticulum (mt-ER) complexes. Within these complexes, mitochondria significantly change morphology and reduce activity. The mt-ER complexes persist throughout oocyte growth until early embryogenesis. During cleavage, they are unevenly segregated to the micromeres that form the embryo body. Our results suggest that in Chelifer, the Balbiani body plays a role in mitochondrial multiplication. We also discuss the role of the mt-ER complexes and propose that they promote low activity of mitochondria to protect mtDNA and supply the embryo with substantial organelles for the early stages of development.

Keywords:  Balbiani body; Chelicerata; Embryo nutrition; Mitochondria activity; Oogenesis; Organelle interactions

DOI:  https://doi.org/10.1016/j.ydbio.2025.08.020
Genes Cells. 2025 Sep;30(5): e70045

Loss of Nuclear Protein Dyro Causes Abnormalities in Nurse Cell Nuclei and Abort Oogenesis at Mid-Oogenesis Checkpoint.

Takamoto Shima, Yuuki Kawabata, Yoshimasa Yagi.

  The mid-oogenesis checkpoint in Drosophila melanogaster functions to optimize nutrient usage by triggering abortion of oogenesis when females are starved or when developmental defects arise in the egg chamber. In the Dyro mutant, which encodes a nuclear factor, oogenesis is aborted during stages 8-9, corresponding to the mid-oogenesis checkpoint. To investigate the relationship between Dyro and this checkpoint, we analyzed the phenotype of the Dyro mutant. Mosaic analysis showed that loss of Dyro in germline cells results in female sterility. Although inhibition of programmed cell death suppressed germline cell death during oogenesis, it failed to rescue the fertility of Dyro mutants, suggesting that oogenesis arrest in the Dyro mutant is not due to misregulation of the cell death signal. We then examined germline cell defects in the Dyro mutant and observed morphological abnormalities in the nucleoli and chromosomes of nurse cells. The chromosomes in Dyro mutant nurse cells were not fully dispersed, and the nucleoli were confined to small spaces between thickened chromosomes. These findings suggest that Dyro plays an important role in nurse cells and that loss of Dyro leads to defects in the chromosomes and nuclei of nurse cells, which leads to abortion of oogenesis.

Keywords:  Drosophila; nurse cell; oogenesis

DOI:  https://doi.org/10.1111/gtc.70045
Mol Hum Reprod. 2025 Sep 04. pii: gaaf044. [Epub ahead of print]

The impact of maternal diet-induced obesity on offspring primordial oocyte mitochondria at birth and at weaning.

Waleed F A Marei, Inne Xhonneux, Axelle Buydens, Isabel Pintelon, Ben Meulders, Silke Andries, Jo L M R Leroy.

  Maternal diet-induced obesity (DIO) may affect adult offspring oocyte quality due to mitochondrial dysfunction. Here, we investigated whether offspring of DIO mothers exhibit mitochondrial abnormalities in their primordial follicle oocytes (PFOs) already at birth, and if (further) alterations can be detected at weaning. Female Swiss mice were fed a control or obesogenic diet for 7 weeks before mating, and throughout pregnancy and lactation. Offspring ovaries were collected at birth and at weaning, Offspring PFOs were examined by transmission electron microscopy of ovarian sections. Key markers of cell stress (HSP70), mitochondrial biogenesis (PGC-1α), mtDNA replication (TFAM), fusion (MFN2, OPA1), and fission (DRP1) were examined using immunofluorescence and confocal microscopy. Maternal DIO did not alter HSP70 or PGC-1α expression in the PFOs at birth, suggesting that cellular homeostasis and mitochondrial biogenesis were unaffected. TFAM expression was reduced at both time points. DRP1 and cytoplasmic OPA1 expression were reduced at birth, but without ultrastructural changes in mitochondrial shape and density, suggesting that these alterations are regulatory. No inborn mitochondrial structural abnormalities could be detected. In contrast, at weaning, offspring born-to and nursed-by DIO mothers exhibited high number of lipid droplets (LDs) in their ovaries, some of which were detectable in the PFOs, while no LDs were detected in the PFOs of the controls. Maternal DIO increased PGC-1α expression, suggesting postnatal effects on PFO mitochondrial biogenesis. MFN2 and OPA1 expression also increased, together with increased mitochondrial elongation and a reduced mitochondrial density. Mitochondrial abnormalities such as vacuolation, loose inner membranes, and also the number of detected autophagosomes and signs of lipophagy were significantly increased by maternal DIO. In conclusion, the oocyte mitochondrial structural abnormalities previously reported in adult offspring from DIO mothers were not detected in the PFOs at birth. Significant changes in primordial follicles linked to maternal DIO were detected only at weaning.

Keywords:  ilpid droplets; intergenerational diseases; lactation; lipotoxicity; maternal obesity; mitochondria; oocyte quality; primordial follicle; puberty

DOI:  https://doi.org/10.1093/molehr/gaaf044
bioRxiv. 2025 Aug 25. pii: 2025.08.24.672014. [Epub ahead of print]

Adipocyte-Derived Amino Acid Storage Proteins are Required for Germline Stem Cell Maintenance in Adult Drosophila Females.

Anna B Zike, Madison G Abel, Robert C Eisman, Lesley N Weaver.

Tissue homeostasis is dependent on precise coordination between endocrine organs in response to changes in organism physiology. Secreted circulating factors from adipocytes (called adipokines) regulate the behavior of stem cell lineages in peripheral tissues in multiple organisms. In addition to their endocrine roles, Drosophila adipocytes store and secrete amino acid storage proteins throughout development. During the larval feeding period, adipocytes secrete storage proteins into the hemolymph, which are reabsorbed by the adipose tissue during metamorphosis to control adult organ size and fertility. Despite the known functions for storage proteins during the larval stages, their requirement during Drosophila adulthood and reproduction are uncharacterized. We discover that adipocyte-specific knockdown of the storage proteins Larval serum protein 1 ( Lsp1 ) α/β/γ and Larval serum protein 2 ( Lsp2 ) results in a decrease in GSC maintenance. We further reveal that decreased GSC number is due to downregulation of Target of Rapamycin (TOR) signaling in GSCs, suggesting compromised amino acid sensing directly in GSCs. We also find that the proteins that mediate storage protein adipocyte reabsorption, Fat body protein 1 (Fbp1) and Fat body protein 2 (Fbp2), are expressed in ovarian follicle cells. Intriguingly, Fbp1 nor Fbp2 appear to be required in follicle cells for GSC maintenance, suggesting undiscovered requirements for amino acid storage proteins in oogenesis. Our results highlight a novel role for Drosophila amino acid storage proteins during adulthood and in regulating tissue stem cell lineages.

DOI: https://doi.org/10.1101/2025.08.24.672014
Biol Reprod. 2025 Sep 05. pii: ioaf204. [Epub ahead of print]

Imaging Transzonal Projections in the Cumulus-Oocyte Complexes: challenges and solutions†.

Mathilde Marchais, Alexandre Bastien, Elolo Karen Nenonene, Edouard W Khandjian, Isabelle Gilbert, Claude Robert.

  Deep 3D imaging of oocytes shows several difficulties. Their large size, spherical shape causes depth-dependent artefactual shadow in the middle, resulting from refractive index mismatches induced by turbid organelles and lipid droplets. These mismatches lead to optical aberrations, increasing the laser spot size at the confocal pinhole plan and causing significant attenuation of fluorescence intensity making difficult to clearly image fine structures such as the transzonal projections (TZPs) connecting cumulus cells and the oocyte. To overcome these challenges, various methods of sample preparation and confocal imagery settings were compared. To clearly show the depth limitation, a clearing protocol was used to image entire fixed embryos. As expected, limiting diffraction namely by removing lipid droplets and harmonizing the extra- and intracellular medium resulted in more uniform staining and distribution, compared to uncleared specimens. The density of the cumulus cloud and fixation protocols were shown to have a profound impact on image quality. Gentle partial stripping and low fixation reduced noise in imagery, while permeabilization with triton enhanced antibody penetration resulting in efficient protein labelling with the zona pellucida enclosed TZPs. Control samples were employed to exemplify unspecific and specific signals to determine optimal confocal settings. Careful consideration of confocal parameters was shown to be crucial for well-adjusted imagery. Moreover, the choice of mounting medium and slide assembly impacts the shape and resolution of the specimen. These findings provide valuable insights into challenges associated with cumulus-oocyte complex imaging, offering solutions for optimizing sample preparation and image quality.

Keywords:  confocal imagery; cumulus cells; oocyte; protein localization; transzonal projections

DOI:  https://doi.org/10.1093/biolre/ioaf204