bims-cebooc 2024-06-23 papers

bims-cebooc

Biomed News

on Cell biology of oocytes

Issue of 2024–06–23
fiveteen papers selected by
Gabriele Zaffagnini, Centre for Genomic Regulation

The maintenance of oocytes in the mammalian ovary involves extreme protein longevity.
Single-cell proteomics reveals decreased abundance of proteostasis and meiosis proteins in advanced maternal age oocytes.
Transcriptomic Analysis of the Spatiotemporal Axis of Oogenesis and Fertilization in C. elegans.
How germ granules promote germ cell fate.
An egg sabotaging mechanism drives non-Mendelian transmission in mice.
Dzip1 is dynamically expressed in the vertebrate germline and regulates the development of Xenopus primordial germ cells.
Maternal loss-of-function of Nlrp2 results in failure of epigenetic reprogramming in mouse oocytes.
The chromatin-associated 53BP1 ortholog, HSR-9, regulates recombinational repair and X chromosome segregation in the Caenorhabditis elegans germ line.
Genome organization regulates nuclear pore complex formation and promotes differentiation during Drosophila oogenesis.
Kinesin motor KIF16A regulates microtubule stability and actin-dependent spindle migration in mouse oocyte meiosis.
The maternal protein NLRP5 stabilizes UHRF1 in the cytoplasm: implication for the pathogenesis of multilocus imprinting disturbance.
Estrogen influences the transzonal projection assembly of cumulus-oocyte complexes through G protein-coupled estrogen receptor during goat follicle development.
Arf6 GTPase deficiency leads to porcine oocyte quality decline during aging.
Greatwall-Endos-PP2A/B55Twins network regulates translation and stability of maternal transcripts in the Drosophila oocyte-to-embryo transition.
DNA replication in early mammalian embryos is patterned, predisposing lamina-associated regions to fragility.

Nat Cell Biol. 2024 Jun 20.

The maintenance of oocytes in the mammalian ovary involves extreme protein longevity.

Katarina Harasimov, Rebecca L Gorry, Luisa M Welp, Sarah Mae Penir, Yehor Horokhovskyi, Shiya Cheng, Katsuyoshi Takaoka, Alexandra Stützer, Ann-Sophie Frombach, Ana Lisa Taylor Tavares, Monika Raabe, Sara Haag, Debojit Saha, Katharina Grewe, Vera Schipper, Silvio O Rizzoli, Henning Urlaub, Juliane Liepe, Melina Schuh.

Women are born with all of their oocytes. The oocyte proteome must be maintained with minimal damage throughout the woman's reproductive life, and hence for decades. Here we report that oocyte and ovarian proteostasis involves extreme protein longevity. Mouse ovaries had more extremely long-lived proteins than other tissues, including brain. These long-lived proteins had diverse functions, including in mitochondria, the cytoskeleton, chromatin and proteostasis. The stable proteins resided not only in oocytes but also in long-lived ovarian somatic cells. Our data suggest that mammals increase protein longevity and enhance proteostasis by chaperones and cellular antioxidants to maintain the female germline for long periods. Indeed, protein aggregation in oocytes did not increase with age and proteasome activity did not decay. However, increasing protein longevity cannot fully block female germline senescence. Large-scale proteome profiling of ~8,890 proteins revealed a decline in many long-lived proteins of the proteostasis network in the aging ovary, accompanied by massive proteome remodeling, which eventually leads to female fertility decline.

DOI: https://doi.org/10.1038/s41556-024-01442-7
bioRxiv. 2024 May 24. pii: 2024.05.23.595547. [Epub ahead of print]

Single-cell proteomics reveals decreased abundance of proteostasis and meiosis proteins in advanced maternal age oocytes.

S Galatidou, A Petelski, A Pujol, K Lattes, L B Latorraca, T Fair, M Popovic, R Vassena, N Slavov, M Barragan.

Advanced maternal age is associated with a decline in oocyte quality, which often leads to reproductive failure in humans. However, the mechanisms behind this age-related decline remain unclear. To gain insights into this phenomenon, we applied plexDIA, a multiplexed, single-cell mass spectrometry method, to analyze the proteome of oocytes from both young women and women of advanced maternal age. Our findings primarily revealed distinct proteomic profiles between immature fully grown germinal vesicle and mature metaphase II oocytes. Importantly, we further show that a woman's age is associated with changes in her oocyte proteome. Specifically, when compared to oocytes obtained from young women, advanced maternal age oocytes exhibited lower levels of the proteasome and TRiC complex, as well as other key regulators of proteostasis and meiosis. This suggests that aging adversely affects the proteostasis and meiosis networks in human oocytes. The proteins identified in this study hold potential as targets for improving oocyte quality and may guide future studies into the molecular processes underlying oocyte aging.

DOI: https://doi.org/10.1101/2024.05.23.595547
bioRxiv. 2024 Jun 04. pii: 2024.06.03.597235. [Epub ahead of print]

Transcriptomic Analysis of the Spatiotemporal Axis of Oogenesis and Fertilization in C. elegans.

Yangqi Su, Jonathan Shea, Darla DeStephanis, Zhengchang Su.

The oocyte germline of the C. elegans hermaphrodite presents a unique model to study the formation of oocytes. However, the size of the model animal and difficulties in retrieval of specific stages of the germline have obviated closer systematic studies of this process throughout the years. Here, we present a transcriptomic level analysis into the oogenesis of C. elegans hermaphrodites. We dissected a hermaphrodite gonad into seven sections corresponding to the mitotic distal region, the pachytene, the diplotene, the early diakinesis region and the 3 most proximal oocytes, and deeply sequenced the transcriptome of each of them along with that of the fertilized egg using a single-cell RNA-seq protocol. We identified specific gene expression events as well as gene splicing events in finer detail along the oocyte germline and provided novel insights into underlying mechanisms of the oogenesis process. Furthermore, through careful review of relevant research literature coupled with patterns observed in our analysis, we attempt to delineate transcripts that may serve functions in the interaction between the germline and cells of the somatic gonad. These results expand our knowledge of the transcriptomic space of the C. elegans germline and lay a foundation on which future studies of the germline can be based upon.

DOI: https://doi.org/10.1101/2024.06.03.597235
Nat Rev Genet. 2024 Jun 18.

How germ granules promote germ cell fate.

Melissa C Pamula, Ruth Lehmann.

Germ cells are the only cells in the body capable of giving rise to a new organism, and this totipotency hinges on their ability to assemble membraneless germ granules. These specialized RNA and protein complexes are hallmarks of germ cells throughout their life cycle: as embryonic germ granules in late oocytes and zygotes, Balbiani bodies in immature oocytes, and nuage in maturing gametes. Decades of developmental, genetic and biochemical studies have identified protein and RNA constituents unique to germ granules and have implicated these in germ cell identity, genome integrity and gamete differentiation. Now, emerging research is defining germ granules as biomolecular condensates that achieve high molecular concentrations by phase separation, and it is assigning distinct roles to germ granules during different stages of germline development. This organization of the germ cell cytoplasm into cellular subcompartments seems to be critical not only for the flawless continuity through the germline life cycle within the developing organism but also for the success of the next generation.

DOI: https://doi.org/10.1038/s41576-024-00744-8
bioRxiv. 2024 Feb 23. pii: 2024.02.22.581453. [Epub ahead of print]

An egg sabotaging mechanism drives non-Mendelian transmission in mice.

Frances E Clark, Naomi L Greenberg, Duilio M Z A Silva, Emily Trimm, Morgan Skinner, R Zaak Walton, Leah F Rosin, Michael A Lampson, Takashi Akera.

During meiosis, homologous chromosomes segregate so that alleles are transmitted equally to haploid gametes, following Mendel's Law of Segregation. However, some selfish genetic elements drive in meiosis to distort the transmission ratio and increase their representation in gametes. The established paradigms for drive are fundamentally different for female vs male meiosis. In male meiosis, selfish elements typically kill gametes that do not contain them. In female meiosis, killing is predetermined, and selfish elements bias their segregation to the single surviving gamete (i.e., the egg in animal meiosis). Here we show that a selfish element on mouse chromosome 2, R2d2 , drives using a hybrid mechanism in female meiosis, incorporating elements of both male and female drivers. If R2d2 is destined for the polar body, it manipulates segregation to sabotage the egg by causing aneuploidy that is subsequently lethal in the embryo, so that surviving progeny preferentially contain R2d2 . In heterozygous females, R2d2 orients randomly on the metaphase spindle but lags during anaphase and preferentially remains in the egg, regardless of its initial orientation. Thus, the egg genotype is either euploid with R2d2 or aneuploid with both homologs of chromosome 2, with only the former generating viable embryos. Consistent with this model, R2d2 heterozygous females produce eggs with increased aneuploidy for chromosome 2, increased embryonic lethality, and increased transmission of R2d2 . In contrast to a male meiotic driver, which kills its sister gametes produced as daughter cells in the same meiosis, R2d2 eliminates "cousins" produced from meioses in which it should have been excluded from the egg.

DOI: https://doi.org/10.1101/2024.02.22.581453
Dev Biol. 2024 Jun 14. pii: S0012-1606(24)00147-7. [Epub ahead of print]514 28-36

Dzip1 is dynamically expressed in the vertebrate germline and regulates the development of Xenopus primordial germ cells.

Aurora Turgeon, Jia Fu, Divyanshi, Meng Ma, Zhigang Jin, Hyojeong Hwang, Meining Li, Huanyu Qiao, Wenyan Mei, Jing Yang.

  Primordial germ cells (PGCs) are the precursors of sperms and oocytes. Proper development of PGCs is crucial for the survival of the species. In many organisms, factors responsible for PGC development are synthesized during early oogenesis and assembled into the germ plasm. During early embryonic development, germ plasm is inherited by a few cells, leading to the formation of PGCs. While germline development has been extensively studied, how components of the germ plasm regulate PGC development is not fully understood. Here, we report that Dzip1 is dynamically expressed in vertebrate germline and is a novel component of the germ plasm in Xenopus and zebrafish. Knockdown of Dzip1 impairs PGC development in Xenopus embryos. At the molecular level, Dzip1 physically interacts with Dazl, an evolutionarily conserved RNA-binding protein that plays a multifaced role during germline development. We further showed that the sequence between amino acid residues 282 and 550 of Dzip1 is responsible for binding to Dazl. Disruption of the binding between Dzip1 and Dazl leads to defective PGC development. Taken together, our results presented here demonstrate that Dzip1 is dynamically expressed in the vertebrate germline and plays a novel function during Xenopus PGC development.

Keywords:  Dazl; Dzip1; Germ plasm; Germline development; Primordial germ cell; Xenopus

DOI:  https://doi.org/10.1016/j.ydbio.2024.06.003
Res Sq. 2024 Jun 04. pii: rs.3.rs-4457414. [Epub ahead of print]

Maternal loss-of-function of Nlrp2 results in failure of epigenetic reprogramming in mouse oocytes.

Zahra Anvar, Michael D Jochum, Imen Chakchouk, Momal Sharif, Hannah Demond, Alvin K To, Daniel C Kraushaar, Ying-Wooi Wan, Simon Andrews, Gavin Kelsey, Ignatia B Veyver.

   Background: NLRP2 belongs to the subcortical maternal complex (SCMC) of mammalian oocytes and preimplantation embryos. This multiprotein complex, encoded by maternal-effect genes, plays a pivotal role in the zygote-to-embryo transition, early embryogenesis, and epigenetic (re)programming. The maternal inactivation of genes encoding SCMC proteins has been linked to infertility and subfertility in mice and humans. However, the underlying molecular mechanisms for the diverse functions of the SCMC, particularly how this cytoplasmic structure influences DNA methylation, which is a nuclear process, are not fully understood.
Results: We undertook joint transcriptome and DNA methylome profiling of pre-ovulatory germinal-vesicle oocytes from Nlrp2-null, heterozygous (Het), and wild-type (WT) female mice. We identified numerous differentially expressed genes (DEGs) in Het and Nlrp2-null when compared to WT oocytes. The genes for several crucial factors involved in oocyte transcriptome modulation and epigenetic reprogramming, such as DNMT1, UHRF1, KDM1B and ZFP57 were overexpressed in Het and Nlrp2-null oocytes. Absence or reduction of Nlrp2, did not alter the distinctive global DNA methylation landscape of oocytes, including the bimodal pattern of the oocyte methylome. Additionally, although the methylation profile of germline differentially methylated regions (gDMRs) of imprinted genes was preserved in oocytes of Het and Nlrp2-null mice, we found altered methylation in oocytes of both genotypes at a small percentage of the oocyte-characteristic hyper- and hypomethylated domains. Through a tiling approach, we identified specific DNA methylation differences between the genotypes, with approximately 1.3% of examined tiles exhibiting differential methylation in Het and Nlrp2-null compared to WT oocytes.
Conclusions: Surprisingly, considering the well-known correlation between transcription and DNA methylation in developing oocytes, we observed no correlation between gene expression differences and gene-body DNA methylation differences in Nlrp2-null versus WT oocytes or Het versus WT oocytes. We therefore conclude that post-transcriptional changes in the stability of transcripts rather than altered transcription is primarily responsible for transcriptome differences in Nlrp2-null and Het oocytes.

Keywords:  DNA methylation; Imprinted genes; Oocyte; Subcortical maternal complex

DOI:  https://doi.org/10.21203/rs.3.rs-4457414/v1
Genetics. 2024 Jun 17. pii: iyae102. [Epub ahead of print]

The chromatin-associated 53BP1 ortholog, HSR-9, regulates recombinational repair and X chromosome segregation in the Caenorhabditis elegans germ line.

Qianyan Li, Sara Hariri, Aashna Calidas, Arshdeep Kaur, Erica Huey, JoAnne Engebrecht.

  53BP1 plays a crucial role in regulating DNA damage repair pathway choice and checkpoint signaling in somatic cells; however, its role in meiosis has remained enigmatic. In this study, we demonstrate that the Caenorhabditis elegans ortholog of 53BP1, HSR-9, associates with chromatin in both proliferating and meiotic germ cells. Notably, HSR-9 is enriched on the X chromosome pair in pachytene oogenic germ cells. HSR-9 is also present at kinetochores during both mitotic and meiotic divisions but does not appear to be essential for monitoring microtubule-kinetochore attachments or tension. Using cytological markers of different steps in recombinational repair, we found that HSR-9 influences the processing of a subset of meiotic double strand breaks into COSA-1-marked crossovers. Additionally, HSR-9 plays a role in meiotic X chromosome segregation under conditions where X chromosomes fail to pair, synapse, and recombine. Together, these results highlight that chromatin-associated HSR-9 has both conserved and unique functions in the regulation of meiotic chromosome behavior.

Keywords:   C. elegans ; 53BP1; HSR-9; checkpoint; meiosis; recombination; sex chromosomes

DOI:  https://doi.org/10.1093/genetics/iyae102
Genes Dev. 2024 Jun 12.

Genome organization regulates nuclear pore complex formation and promotes differentiation during Drosophila oogenesis.

Noor M Kotb, Gulay Ulukaya, Ankita Chavan, Son C Nguyen, Lydia Proskauer, Eric F Joyce, Dan Hasson, Madhav Jagannathan, Prashanth Rangan.

  Genome organization can regulate gene expression and promote cell fate transitions. The differentiation of germline stem cells (GSCs) to oocytes in Drosophila involves changes in genome organization mediated by heterochromatin and the nuclear pore complex (NPC). Heterochromatin represses germ cell genes during differentiation, and NPCs anchor these silenced genes to the nuclear periphery, maintaining silencing to allow for oocyte development. Surprisingly, we found that genome organization also contributes to NPC formation, mediated by the transcription factor Stonewall (Stwl). As GSCs differentiate, Stwl accumulates at boundaries between silenced and active gene compartments. Stwl at these boundaries plays a pivotal role in transitioning germ cell genes into a silenced state and activating a group of oocyte genes and nucleoporins (Nups). The upregulation of these Nups during differentiation is crucial for NPC formation and further genome organization. Thus, cross-talk between genome architecture and NPCs is essential for successful cell fate transitions.

Keywords:  LAD; NPC; TAD; differentiation; genome organization; heterochromatin; lamin; nucleoporins

DOI:  https://doi.org/10.1101/gad.351402.123
FASEB J. 2024 Jul 15. 38(13): e23750

Kinesin motor KIF16A regulates microtubule stability and actin-dependent spindle migration in mouse oocyte meiosis.

Wei Wang, Zhenhu Shi, Dandan Zhang, Wenwen Hou, Huijie Ma, Xinyu Liu, Yongteng Zhang, Jinbao Zhu, Zaishan Yang, Bo Jia, Qimei Xu, Yunhai Zhang, Mianqun Zhang.

  Kif16A, a member of the kinesin-3 family of motor proteins, has been shown to play crucial roles in inducing mitotic arrest, apoptosis, and mitotic cell death. However, its roles during oocyte meiotic maturation have not been fully defined. In this study, we report that Kif16A exhibits unique accumulation on the spindle apparatus and colocalizes with microtubule fibers during mouse oocyte meiotic maturation. Targeted depletion of Kif16A using gene-targeting siRNA disrupts the progression of the meiotic cell cycle. Furthermore, Kif16A depletion leads to aberrant spindle assembly and chromosome misalignment in oocytes. Our findings also indicate that Kif16A depletion reduces tubulin acetylation levels and compromises microtubule resistance to depolymerizing drugs, suggesting its crucial role in microtubule stability maintenance. Notably, we find that the depletion of Kif16A results in a notably elevated incidence of defective kinetochore-microtubule attachments and the absence of BubR1 localization at kinetochores, suggesting a critical role for Kif16A in the activation of the spindle assembly checkpoint (SAC) activity. Additionally, we observe that Kif16A is indispensable for proper actin filament distribution, thereby impacting spindle migration. In summary, our findings demonstrate that Kif16A plays a pivotal role in regulating microtubule and actin dynamics crucial for ensuring both spindle assembly and migration during mouse oocyte meiotic maturation.

Keywords:  KIF16A; kinetochore‐microtubule attachment; oocyte meiosis; spindle assembly; spindle migration

DOI:  https://doi.org/10.1096/fj.202400989R
Hum Mol Genet. 2024 Jun 13. pii: ddae096. [Epub ahead of print]

The maternal protein NLRP5 stabilizes UHRF1 in the cytoplasm: implication for the pathogenesis of multilocus imprinting disturbance.

Motoko Unoki, Shuhei Uemura, Akihiro Fujimoto, Hiroyuki Sasaki.

  We have recently discovered that the so-called subcortical maternal complex (SCMC) proteins composing of cytoplasmic lattices are destabilized in Uhrf1 knockout murine fully grown oocytes (FGOs). Here we report that human UHRF1 interacts with human NLRP5 and OOEP, which are core components of the SCMC. Moreover, NLRP5 and OOEP interact with DPPA3, which is an essential factor for exporting UHRF1 from the nucleus to the cytoplasm in oocytes. We identify that NLRP5, not OOEP, stabilizes UHRF1 protein in the cytoplasm utilizing specifically engineered cell lines mimicking UHRF1 status in oocytes and preimplantation embryos. Further, UHRF1 is destabilized both in the cytoplasm and nucleus of Nlrp5 knockout murine FGOs. Since pathogenic variants of the SCMC components frequently cause multilocus imprinting disturbance and UHRF1 is essential for maintaining CpG methylation of imprinting control regions during preimplantation development, our results suggest possible pathogenesis behind the disease, which has been a long-standing mystery.

Keywords:  MLID; NLRP5; SCMC; UHRF1; multilocus imprinting disturbance

DOI:  https://doi.org/10.1093/hmg/ddae096
Mol Reprod Dev. 2024 Jun;91(6): e23763

Estrogen influences the transzonal projection assembly of cumulus-oocyte complexes through G protein-coupled estrogen receptor during goat follicle development.

Rui Xu, Dongxu Wen, Lu Yin, Yaju Tang, Sihai Lu, Yan Gao, Meng-Hao Pan, Bin Han, Baohua Ma.

  Estrogen is an important hormone that plays a role in regulating follicle development and oocyte maturation. Transzonal projections (TZPs) act as communication bridges between follicle somatic cells and oocytes, and their dynamic changes are critical for oocyte development and maturation. However, the roles and mechanisms of estrogen in regulating TZPs during follicular development are not yet understood. We found that the proportion of oocytes spontaneously resuming meiosis increases as the follicle grows, which is accompanied by rising estrogen levels in follicles and decreasing TZPs in cumulus-oocyte complex. To further explore the effect of elevated estrogen levels on TZP assembly, additional estrogen was added to the culture system. The increased estrogen level significantly decreased the mRNA and protein expression levels of TZP assembly-related genes. Subsequent research revealed that TZP regulation by estrogen was mediated by the membrane receptor GPER and downstream ERK1/2 signaling pathway. In summary, our study suggests that estrogen may regulate goat oocyte meiosis arrest by decreasing TZP numbers via estrogen-mediated GPER activation during follicle development.

Keywords:  estrogen; goat follicle; oocyte; transzonal projections

DOI:  https://doi.org/10.1002/mrd.23763
FASEB J. 2024 Jul 15. 38(13): e23739

Arf6 GTPase deficiency leads to porcine oocyte quality decline during aging.

Kun-Huan Zhang, Le Jiao, Yue Wang, Shao-Chen Sun.

  Arf6 is a member of ADP-ribosylation factor (Arf) family, which is widely implicated in the regulation of multiple physiological processes including endocytic recycling, cytoskeletal organization, and membrane trafficking during mitosis. In this study, we investigated the potential relationship between Arf6 and aging-related oocyte quality, and its roles on organelle rearrangement and cytoskeleton dynamics in porcine oocytes. Arf6 expressed in porcine oocytes throughout meiotic maturation, and it decreased in aged oocytes. Disruption of Arf6 led to the failure of cumulus expansion and polar body extrusion. Further analysis indicated that Arf6 modulated ac-tubulin for meiotic spindle organization and microtubule stability. Besides, Arf6 regulated cofilin phosphorylation and fascin for actin assembly, which further affected spindle migration, indicating the roles of Arf6 on cytoskeleton dynamics. Moreover, the lack of Arf6 activity caused the dysfunction of Golgi and ER for protein synthesis and signal transduction. Mitochondrial dysfunction was also observed in Arf6-deficient porcine oocytes, which was supported by the increased ROS level and abnormal membrane potential. In conclusion, our results reported that insufficient Arf6 was related to aging-induced oocyte quality decline through spindle organization, actin assembly, and organelle rearrangement in porcine oocytes.

Keywords:  Arf6; actin; organelle; porcine oocyte; spindle

DOI:  https://doi.org/10.1096/fj.202400893R
Open Biol. 2024 Jun;14(6): 240065

Greatwall-Endos-PP2A/B55Twins network regulates translation and stability of maternal transcripts in the Drosophila oocyte-to-embryo transition.

Hélène Rangone, Laura Bond, Timothy T Weil, David M Glover.

  The transition from oocyte to embryo requires translation of maternally provided transcripts that in Drosophila is activated by Pan Gu kinase to release a rapid succession of 13 mitotic cycles. Mitotic entry is promoted by several protein kinases that include Greatwall/Mastl, whose Endosulfine substrates antagonize Protein Phosphatase 2A (PP2A), facilitating mitotic Cyclin-dependent kinase 1/Cyclin B kinase activity. Here we show that hyperactive greatwallScant can not only be suppressed by mutants in its Endos substrate but also by mutants in Pan Gu kinase subunits. Conversely, mutants in me31B or trailer hitch, which encode a complex that represses hundreds of maternal mRNAs, enhance greatwallScant . Me31B and Trailer Hitch proteins, known substrates of Pan Gu kinase, copurify with Endos. This echoes findings that budding yeast Dhh1, orthologue of Me31B, associates with Igo1/2, orthologues of Endos and substrates of the Rim15, orthologue of Greatwall. endos-derived mutant embryos show reduced Me31B and elevated transcripts for the mitotic activators Cyclin B, Polo and Twine/Cdc25. Together, our findings demonstrate a previously unappreciated conservation of the Greatwall-Endosulfine pathway in regulating translational repressors and its interactions with the Pan Gu kinase pathway to regulate translation and/or stability of maternal mRNAs upon egg activation.

Keywords:  Drosophila; Endosulfine; Greatwall; Pan Gu kinase; maternal transcripts; oocyte-to-embryo transition

DOI:  https://doi.org/10.1098/rsob.240065
Nat Commun. 2024 Jun 19. 15(1): 5247

DNA replication in early mammalian embryos is patterned, predisposing lamina-associated regions to fragility.

Shuangyi Xu, Ning Wang, Michael V Zuccaro, Jeannine Gerhardt, Rajan Iyyappan, Giovanna Nascimento Scatolin, Zongliang Jiang, Timour Baslan, Amnon Koren, Dieter Egli.

DNA replication in differentiated cells follows a defined program, but when and how it is established during mammalian development is not known. Here we show using single-cell sequencing, that late replicating regions are established in association with the B compartment and the nuclear lamina from the first cell cycle after fertilization on both maternal and paternal genomes. Late replicating regions contain a relative paucity of active origins and few but long genes and low G/C content. In both bovine and mouse embryos, replication timing patterns are established prior to embryonic genome activation. Chromosome breaks, which form spontaneously in bovine embryos at sites concordant with human embryos, preferentially locate to late replicating regions. In mice, late replicating regions show enhanced fragility due to a sparsity of dormant origins that can be activated under conditions of replication stress. This pattern predisposes regions with long neuronal genes to fragility and genetic change prior to separation of soma and germ cell lineages. Our studies show that the segregation of early and late replicating regions is among the first layers of genome organization established after fertilization.

DOI: https://doi.org/10.1038/s41467-024-49565-7