bims-cebooc Biomed News
on Cell biology of oocytes
Issue of 2024‒09‒01
nine papers selected by
Gabriele Zaffagnini, Centre for Genomic Regulation
  1. Embryonic genome instability upon DNA replication timing program emergence.
  2. Homozygosity for a stop-gain variant in CCDC201 causes primary ovarian insufficiency.
  3. A conserved germline-specific Dsn1 alternative splice isoform supports oocyte and embryo development.
  4. Full-field optical coherence microscopy enables high-resolution label-free imaging of the dynamics of live mouse oocytes and early embryos.
  5. Chromatin remodeler CHD4 establishes chromatin states required for ovarian reserve formation, maintenance, and germ cell survival.
  6. Lineage-based scaling of germline intercellular bridges during oogenesis.
  7. Pramel15 facilitates zygotic nuclear DNMT1 degradation and DNA demethylation.
  8. Behavior of Assembled Promyelocytic Leukemia Nuclear Bodies upon Asymmetric Division in Mouse Oocytes.
  9. IP3R1 is required for meiotic progression and embryonic development by regulating mitochondrial calcium and oxidative damage.
  1. Nature. 2024 Aug 28.
    Embryonic genome instability upon DNA replication timing program emergence.
    Saori Takahashi, Hirohisa Kyogoku, Takuya Hayakawa, Hisashi Miura, Asami Oji, Yoshiko Kondo, Shin-Ichiro Takebayashi, Tomoya S Kitajima, Ichiro Hiratani.
      Faithful DNA replication is essential for genome integrity1-4. Under-replicated DNA leads to defects in chromosome segregation, which are common during embryogenesis5-8. However, the regulation of DNA replication remains poorly understood in early mammalian embryos. Here we constructed a single-cell genome-wide DNA replication atlas of pre-implantation mouse embryos and identified an abrupt replication program switch accompanied by a transient period of genomic instability. In 1- and 2-cell embryos, we observed the complete absence of a replication timing program, and the entire genome replicated gradually and uniformly using extremely slow-moving replication forks. In 4-cell embryos, a somatic-cell-like replication timing program commenced abruptly. However, the fork speed was still slow, S phase was extended, and markers of replication stress, DNA damage and repair increased. This was followed by an increase in break-type chromosome segregation errors specifically during the 4-to-8-cell division with breakpoints enriched in late-replicating regions. These errors were rescued by nucleoside supplementation, which accelerated fork speed and reduced the replication stress. By the 8-cell stage, forks gained speed, S phase was no longer extended and chromosome aberrations decreased. Thus, a transient period of genomic instability exists during normal mouse development, preceded by an S phase lacking coordination between replisome-level regulation and megabase-scale replication timing regulation, implicating a link between their coordination and genome stability.
    DOI:  https://doi.org/10.1038/s41586-024-07841-y
  2. Nat Genet. 2024 Aug 27.
    Homozygosity for a stop-gain variant in CCDC201 causes primary ovarian insufficiency.
    DBDS Genomic Consortium
      Age at menopause (AOM) has a substantial impact on fertility and disease risk. While many loci with variants that associate with AOM have been identified through genome-wide association studies (GWAS) under an additive model, other genetic models are rarely considered1. Here through GWAS meta-analysis under the recessive model of 174,329 postmenopausal women from Iceland, Denmark, the United Kingdom (UK; UK Biobank) and Norway, we study low-frequency variants with a large effect on AOM. We discovered that women homozygous for the stop-gain variant rs117316434 (A) in CCDC201 (p.(Arg162Ter), minor allele frequency ~1%) reached menopause 9 years earlier than other women (P = 1.3 × 10-15). The genotype is present in one in 10,000 northern European women and leads to primary ovarian insufficiency in close to half of them. Consequently, homozygotes have fewer children, and the age at last childbirth is 5 years earlier (P = 3.8 × 10-5). The CCDC201 gene was only found in humans in 2022 and is highly expressed in oocytes. Homozygosity for CCDC201 loss-of-function has a substantial impact on female reproductive health, and homozygotes would benefit from reproductive counseling and treatment for symptoms of early menopause.
    DOI:  https://doi.org/10.1038/s41588-024-01885-6
  3. Curr Biol. 2024 Aug 17. pii: S0960-9822(24)01028-5. [Epub ahead of print]
    A conserved germline-specific Dsn1 alternative splice isoform supports oocyte and embryo development.
    Jimmy Ly, Cecilia S Blengini, Sarah L Cady, Karen Schindler, Iain M Cheeseman.
      The chromosome segregation and cell division programs associated with somatic mitosis and germline meiosis display dramatic differences such as kinetochore orientation, cohesin removal, or the presence of a gap phase.1,2,3,4,5,6 These changes in chromosome segregation require alterations to the established cell division machinery.5,6 It remains unclear what aspects of kinetochore function and its regulatory control differ between the mitotic and meiotic cell divisions to rewire these core processes. Alternative RNA splicing can generate distinct protein isoforms to allow for the differential control of cell processes across cell types. However, alternative splice isoforms that differentially modulate distinct cell division programs have remained elusive. Here, we demonstrate that mammalian germ cells express an alternative mRNA splice isoform for the kinetochore component, DSN1, a subunit of the MIS12 complex that links the centromeres to spindle microtubules during chromosome segregation. This germline DSN1 isoform bypasses the requirement for Aurora kinase phosphorylation for its centromere localization due to the absence of a key regulatory region allowing DSN1 to display persistent centromere localization. Expression of the germline DSN1 isoform in somatic cells results in constitutive kinetochore localization, chromosome segregation errors, and growth defects, providing an explanation for its tight cell-type-specific expression. Reciprocally, precisely eliminating expression of the germline-specific DSN1 splice isoform in mouse models disrupts oocyte maturation and early embryonic divisions coupled with a reduction in fertility. Together, this work identifies a germline-specific splice isoform for a chromosome segregation component and implicates its role in mammalian fertility.
    Keywords:  alternative splicing; fertility; kinetochore; meiosis; mitosis
    DOI:  https://doi.org/10.1016/j.cub.2024.07.089
  4. Commun Biol. 2024 Aug 27. 7(1): 1057
    Full-field optical coherence microscopy enables high-resolution label-free imaging of the dynamics of live mouse oocytes and early embryos.
    Seweryn Morawiec, Anna Ajduk, Patrycjusz Stremplewski, Brendan F Kennedy, Maciej Szkulmowski.
      High quality label-free imaging of oocytes and early embryos is essential for accurate assessment of their developmental potential, a key element of assisted reproduction procedures. To achieve this goal, we propose full-field optical coherence microscopy (FF-OCM), constructed as a compact module fully integrated with a commercial wide-field fluorescence microscope. Our system achieves optical sectioning in wide-field, high in-plane resolution of 0.5 µm, and high sensitivity to backscattered light. To demonstrate its imaging capabilities, we study live mouse oocytes and embryos at all important stages of meiotic maturation and early embryogenesis. Our system enables visualization of intracellular structures, which are not visible in common bright-field microscopy, i.e., internal structure of nuclear apparatus, cytoskeletal filaments, cellular cortex, cytoplasmic protrusions, or zona pellucida features. Additionally, we visualize and quantify intracellular dynamics like cytoplasmic stirring motion, nuclear envelope fluctuations and nucleolus mobility. Altogether, we demonstrate that FF-OCM is a powerful tool for research in developmental biology that also holds great potential for non-invasive time-lapse monitoring of oocyte and embryo quality in assisted reproduction.
    DOI:  https://doi.org/10.1038/s42003-024-06745-x
  5. bioRxiv. 2024 Aug 13. pii: 2024.08.12.607691. [Epub ahead of print]
    Chromatin remodeler CHD4 establishes chromatin states required for ovarian reserve formation, maintenance, and germ cell survival.
    Yasuhisa Munakata, Mengwen Hu, Yuka Kitamura, 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 (NGO) 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 meiotic arrested NGOs. In addition, CHD4 establishes closed chromatin at the regulatory elements of pro-apoptotic genes in male germ cells, allowing male 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/10.1101/2024.08.12.607691
  6. Development. 2024 Aug 15. pii: dev202676. [Epub ahead of print]151(16):
    Lineage-based scaling of germline intercellular bridges during oogenesis.
    Umayr Shaikh, Kathleen Sherlock, Julia Wilson, William Gilliland, Lindsay Lewellyn.
      The size of subcellular structures must be tightly controlled to maintain normal cell function. Despite its importance, few studies have determined how the size of organelles or other structures is maintained during development, when cells are growing, dividing and rearranging. The developing Drosophila egg chamber is a powerful model in which to study the relative growth rates of subcellular structures. The egg chamber contains a cluster of 16 germline cells, which are connected through intercellular bridges called ring canals. As the egg chamber grows, the germline cells and the ring canals that connect them increase in size. Here, we demonstrate that ring canal size scaling is related to lineage; the largest, 'first-born' ring canals increase in size at a relatively slower rate than ring canals derived from subsequent mitotic divisions. This lineage-based scaling relationship is maintained even if directed transport is reduced, ring canal size is altered, or in egg chambers with twice as many germline cells. Analysis of lines that produce larger or smaller mature eggs reveals that different strategies could be used to alter final egg size.
    Keywords:   Drosophila ; Intercellular bridge; Oogenesis; Ring canal
    DOI:  https://doi.org/10.1242/dev.202676
  7. Nat Commun. 2024 Aug 25. 15(1): 7310
    Pramel15 facilitates zygotic nuclear DNMT1 degradation and DNA demethylation.
    Jiajun Tan, Yingfeng Li, Xiang Li, Xiaoxiao Zhu, Liping Liu, Hua Huang, Jiahua Wei, Hailing Wang, Yong Tian, Zhigao Wang, Zhuqiang Zhang, Bing Zhu.
      In mammals, global passive demethylation contributes to epigenetic reprogramming during early embryonic development. At this stage, the majority of DNA-methyltransferase 1 (DNMT1) protein is excluded from nucleus, which is considered the primary cause. However, whether the remaining nuclear activity of DNMT1 is regulated by additional mechanisms is unclear. Here, we report that nuclear DNMT1 abundance is finetuned through proteasomal degradation in mouse zygotes. We identify a maternal factor, Pramel15, which targets DNMT1 for degradation via Cullin-RING E3 ligases. Loss of Pramel15 elevates DNMT1 levels in the zygote pronuclei, impairs zygotic DNA demethylation, and causes a stochastic gain of DNA methylation in early embryos. Thus, Pramel15 can modulate the residual level of DNMT1 in the nucleus during zygotic DNA replication, thereby ensuring efficient DNA methylation reprogramming in early embryos.
    DOI:  https://doi.org/10.1038/s41467-024-51614-0
  8. Int J Mol Sci. 2024 Aug 08. pii: 8656. [Epub ahead of print]25(16):
    Behavior of Assembled Promyelocytic Leukemia Nuclear Bodies upon Asymmetric Division in Mouse Oocytes.
    Osamu Udagawa, Ayaka Kato-Udagawa, Seishiro Hirano.
      Promyelocytic leukemia (PML) nuclear bodies (PML-NBs) are core-shell-type membrane-less organelles typically found in the nucleus of mammalian somatic cells but are absent in mouse oocytes. Here, we deliberately induced the assembly of PML-NBs by injecting mRNA encoding human PML protein (hPML VI -sfGFP) into oocytes and investigated their impact on fertilization in which oocyte/embryos undergo multiple types of stresses. Following nuclear membrane breakdown, preassembled hPML VI -sfGFP mRNA-derived PML-NBs (hmdPML-NBs) persisted in the cytoplasm of oocytes, forming less-soluble debris, particularly under stress. Parthenogenetic embryos that successfully formed pronuclei were capable of removing preassembled hmdPML-NBs from the cytoplasm while forming new hmdPML-NBs in the pronucleus. These observations highlight the beneficial aspect of the PML-NB-free nucleoplasmic environment and suggest that the ability to eliminate unnecessary materials in the cytoplasm of metaphase oocytes serves as a potential indicator of the oocyte quality.
    Keywords:  fertilization; membrane-less organelle; nuclear bodies (NBs); oocyte maturation; stress response
    DOI:  https://doi.org/10.3390/ijms25168656
  9. Theriogenology. 2024 Aug 19. pii: S0093-691X(24)00344-3. [Epub ahead of print]229 147-157
    IP3R1 is required for meiotic progression and embryonic development by regulating mitochondrial calcium and oxidative damage.
    Chang Zhang, Xiaoqing Sun, Deyi Wu, Guoxia Wang, Hainan Lan, Xin Zheng, Suo Li.
      Calcium ions (Ca2+) regulate cell proliferation and differentiation and participate in various physiological activities of cells. The calcium transfer protein inositol 1,4,5-triphosphate receptor (IP3R), located between the endoplasmic reticulum (ER) and mitochondria, plays an important role in regulating Ca2+ levels. However, the mechanism by which IP3R1 affects porcine meiotic progression and embryonic development remains unclear. We established a model in porcine oocytes using siRNA-mediated knockdown of IP3R1 to investigate the effects of IP3R1 on porcine oocyte meiotic progression and embryonic development. The results indicated that a decrease in IP3R1 expression significantly enhanced the interaction between the ER and mitochondria. Additionally, the interaction between the ER and the mitochondrial Ca2+ ([Ca2+]m) transport network protein IP3R1-GRP75-VDAC1 was disrupted. The results of the Duolink II in situ proximity ligation assay (PLA) revealed a weakened pairwise interaction between IP3R1-GRP75 and VDAC1 and a significantly increased interaction between GRP75 and VDAC1 after IP3R1 interference, resulting in the accumulation of large amounts of [Ca2+]m. These changes led to mitochondrial oxidative stress, increased the levels of reactive oxygen species (ROS) and reduced ATP production, which hindered the maturation and late development of porcine oocytes and induced apoptosis. Nevertheless, after treat with [Ca2+]m chelating agent ruthenium red (RR) or ROS scavenger N-acetylcysteine (NAC), the oocytes developmental abnormalities, oxidative stress and apoptosis caused by Ca2+ overload were improved. In conclusion, our results indicated IP3R1 is required for meiotic progression and embryonic development by regulating mitochondrial calcium and oxidative damage.
    Keywords:  Ca(2+); ER; IP(3)R1; Mitochondria; Porcine oocytes; ROS
    DOI:  https://doi.org/10.1016/j.theriogenology.2024.08.023
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