scholarly journals Peculiarities of the molecular composition of heterochromatin associated with pronucleoli in mouse embryos

2019 ◽  
Vol 23 (2) ◽  
pp. 129-134 ◽  
Author(s):  
I. O. Bogolyubova ◽  
Z. K. Sailau ◽  
D. S. Bogolyubov
Keyword(s):  
Mouse Embryos ◽  
Molecular Composition ◽  
Epigenetic Mark ◽  
Exon Junction Complex ◽  
Cell Cleavage ◽  
Embryonic Genome ◽  
Early Embryos ◽  
Mammalian Embryos ◽  
Typical Component ◽  
Genome Activation

The nucleus of pre-implantation mammalian embryos is characterized by peculiar structural organization. At the initial stages of cleavage, the nucleus of the embryo contains the so-called nucleolus precursor bodies (NPBs) or pronucleoli rather than functionally active nucleoli. The NPBs are fibrillar electron-dense structures inactive in RNA synthesis. The vast majority of NPBs are surrounded by a ring-shaped zone of transcriptionally inactive heterochromatin. Intriguingly, these zones contain not only tri-methylated histone Н3K9me3 as an epigenetic mark of repressed chromatin but also acetylated histone H4K5ac, a well-known marker of active chromatin. Immunocytochemical data suggest that the molecular composition of this ‘ring heterochromatin’ in mouse embryos changes during the realization of embryonic genome activation events, as well as during artificial suppression of transcription. In zygotes, some factors of mRNA biogenesis including splicing factor SC35 (SRSF2) and basal transcription factor TFIID are detectable in the ring chromatin. At later stages of development, other nuclear proteins such as Y14, a core component of the exon-exon junction complex (EJC), as well as the proteins involved in chromatin remodeling (ATRX, Daxx) are also detectable in this area. A typical component of the ‘ring heterochromatin’ is actin. Anti-actin immunocytochemical labeling is most expressed at the two-cell cleavage stage after activation of the embryonic genome. Indicatively, the molecular composition of the ‘ring heterochromatin’ associated with different NPBs may differ significantly even in the same nucleus. This seems to reflect the functional heterogeneity of morphologically similar NPBs according to their competence to the process of nucleologenesis. Here, we discuss briefly some peculiarities of the molecular composition and possible functions of the NPB-associated heterochromatin in mouse early embryos.

scholarly journals The role of ZFP57 and additional KRAB-zinc finger proteins in the maintenance of human imprinted methylation and multi-locus imprinting disturbances

2020 ◽  
Vol 48 (20) ◽  
pp. 11394-11407
Author(s):  
Ana Monteagudo-Sánchez ◽  
Jose Ramon Hernandez Mora ◽  
Carlos Simon ◽  
Adam Burton ◽  
Jair Tenorio ◽  
...  
Keyword(s):  
Zinc Finger ◽  
Expression Profiling ◽  
Zinc Finger Proteins ◽  
Early Embryogenesis ◽  
Mouse Embryos ◽  
Parental Origin ◽  
Embryonic Genome ◽  
Repressor Complex ◽  
Genome Activation

Abstract Genomic imprinting is an epigenetic process regulated by germline-derived DNA methylation that is resistant to embryonic reprogramming, resulting in parental origin-specific monoallelic gene expression. A subset of individuals affected by imprinting disorders (IDs) displays multi-locus imprinting disturbances (MLID), which may result from aberrant establishment of imprinted differentially methylated regions (DMRs) in gametes or their maintenance in early embryogenesis. Here we investigated the extent of MLID in a family harbouring a ZFP57 truncating variant and characterize the interactions between human ZFP57 and the KAP1 co-repressor complex. By ectopically targeting ZFP57 to reprogrammed loci in mouse embryos using a dCas9 approach, we confirm that ZFP57 recruitment is sufficient to protect oocyte-derived methylation from reprogramming. Expression profiling in human pre-implantation embryos and oocytes reveals that unlike in mice, ZFP57 is only expressed following embryonic-genome activation, implying that other KRAB-zinc finger proteins (KZNFs) recruit KAP1 prior to blastocyst formation. Furthermore, we uncover ZNF202 and ZNF445 as additional KZNFs likely to recruit KAP1 to imprinted loci during reprogramming in the absence of ZFP57. Together, these data confirm the perplexing link between KZFPs and imprint maintenance and highlight the differences between mouse and humans in this respect.

scholarly journals Micronucleus formation causes perpetual unilateral chromosome inheritance in mouse embryos

2016 ◽  
Vol 113 (3) ◽  
pp. 626-631 ◽  
Author(s):  
Cayetana Vázquez-Diez ◽  
Kazuo Yamagata ◽  
Shardul Trivedi ◽  
Jenna Haverfield ◽  
Greg FitzHarris
Keyword(s):  
Chromosome Segregation ◽  
High Frequency ◽  
Mouse Embryos ◽  
Cell Lineages ◽  
Daughter Cells ◽  
Cell Divisions ◽  
Embryonic Genome ◽  
Mammalian Embryos ◽  
Kinetics Of ◽  
Functional Kinetochore

Chromosome segregation defects in cancer cells lead to encapsulation of chromosomes in micronuclei (MN), small nucleus-like structures within which dangerous DNA rearrangements termed chromothripsis can occur. Here we uncover a strikingly different consequence of MN formation in preimplantation development. We find that chromosomes from within MN become damaged and fail to support a functional kinetochore. MN are therefore not segregated, but are instead inherited by one of the two daughter cells. We find that the same MN can be inherited several times without rejoining the principal nucleus and without altering the kinetics of cell divisions. MN motion is passive, resulting in an even distribution of MN across the first two cell lineages. We propose that perpetual unilateral MN inheritance constitutes an unexpected mode of chromosome missegregation, which could contribute to the high frequency of aneuploid cells in mammalian embryos, but simultaneously may serve to insulate the early embryonic genome from chromothripsis.

scholarly journals 2 The landscape of accessible chromatin in bovine oocytes and early embryos

2020 ◽  
Vol 32 (2) ◽  
pp. 125
Author(s):  
H. Ming ◽  
J. Sun ◽  
R. Pasquariello ◽  
J. R. Herrick ◽  
Y. Yuan ◽  
...  
Keyword(s):  
Regulatory Networks ◽  
Bovine Embryo ◽  
Embryonic Genome Activation ◽  
Genome Wide ◽  
Embryonic Genome ◽  
Early Embryos ◽  
Germinal Vesicles ◽  
Genome Activation ◽  
Bovine Oocytes ◽  
Accessible Chromatin

Chromatin reorganization governs gene expression regulation during pre-implantation development. However, the global chromatin landscape and its dynamics in this period remain unexplored in bovine. In this study, we constructed a genome-wide map of accessible chromatin in bovine oocytes and early embryos using an improved assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq). We analysed pools of 20 germinal vesicles or MII oocytes or 2-, 4-, 8-, 16-cell, morula, and blastocyst stage invitro-produced embryos. We conducted ATAC-seq on six pools for each stage and an additional four pools of invivo-derived morula and blastocysts and six replicates using individual Day 14 elongating embryos. We obtained ~110 million paired end reads uniquely mapped to the bovine reference genome for each stage. Hierarchical clustering, t-distributed stochastic neighbour embedding, and principal component analysis showed four distinct patterns for open chromatin status: (1) low accessibility in germinal vesicles and MII oocytes and in 2- and 4-cell embryos; (2) significantly elevated accessibility in 8-cell, 16-cell, and morula embryos; (3) less accessibility in blastocysts; and (4) extremely high accessibility in elongating embryos. This dynamic and sequential chromatin remodelling is consistent with transcription activation during the bovine minor embryonic genome activation from fertilization to 4-cell, major embryonic genome activation at 8-cell, first differentiation at blastocyst and drastic transcription initiation for embryo elongation. Genome-wide characteristics of accessible chromatin showed (1) accessible chromatin near the transcription start sites of active genes and CpG-rich promoters; (2) widespread accessible chromatin regions extensively overlapped with transposable elements; (3) distal peaks preferentially enriched for repeats including LINE, SINE, and LTR from 8-cell to morula embryos, especially for LTR, whereas enrichment in simple repeats were found from oocytes to 4-cell and in elongating embryos; and (4) highly stage-specific transcription factor motifs in distal peaks were unveiled. By integrating the maps of chromatin accessibility with bovine embryo transcriptomes and DNA methylomes, we found promoter accessibility and DNA methylation in bovine embryos correlated with both gene activities and CpG densities. Most importantly, we constructed the regulatory networks of stage-specific expressed genes and stage-specific activated genes with three omics datasets in bovine early embryos and revealed conserved and distinctive transcriptional regulatory networks between invivo- and invitro-derived embryos. This comprehensive analysis revealed critical features of the chromatin landscape and epigenetic reprogramming during bovine early embryo development.

scholarly journals Improving the Quality of Oocytes with the Help of Nucleolotransfer Therapy

2021 ◽  
Vol 14 (4) ◽  
pp. 328
Author(s):  
Michal Benc ◽  
Frantisek Strejcek ◽  
Martin Morovic ◽  
Alexandra Bartkova ◽  
Matej Murin ◽  
...  
Keyword(s):  
Ribosome Biogenesis ◽  
Rrna Synthesis ◽  
Comprehensive Overview ◽  
Compact Structure ◽  
Embryonic Genome Activation ◽  
Embryonic Genome ◽  
Early Embryos ◽  
The One ◽  
Almost All ◽  
Genome Activation

The nucleolus is an important nucleus sub-organelle found in almost all eukaryotic cells. On the one hand, it is known as a differentiated active site of ribosome biogenesis in somatic cells, but on the other hand, in fully grown oocytes, zygotes, and early embryos (up to the major embryonic genome activation), it is in the form of a particular homogenous and compact structure called a fibrillar sphere. Nowadays, thanks to recent studies, we know many important functions of this, no doubt, interesting membraneless nucleus sub-organelle involved in oocyte maturation, embryonic genome activation, rRNA synthesis, etc. However, many questions are still unexplained and remain a mystery. Our aim is to create a comprehensive overview of the recent knowledge on the fibrillar sphere and envision how this knowledge could be utilized in further research in the field of biotechnology and nucleolotransfer therapy.

scholarly journals Embryonic gene transcription in the spiny mouse (Acomys cahirinus): an investigtion into the embryonic genome activation

2018 ◽  
Author(s):  
Jared Mamrot ◽  
David K. Gardner ◽  
Peter Temple-Smith ◽  
Hayley Dickinson
Keyword(s):  
Gene Expression ◽  
Embryonic Development ◽  
Gene Transcription ◽  
De Novo ◽  
Mouse Embryos ◽  
Spiny Mouse ◽  
Acomys Cahirinus ◽  
Embryonic Genome Activation ◽  
Embryonic Genome ◽  
Genome Activation

Our understanding of genetic mechanisms driving early embryonic development is primarily based on experiments conducted on mice, however translation of findings can be limited by physiological differences between mice and humans. To address this, we investigated whether the spiny mouse (Acomys cahirinus) is a closer model of early human embryonic development due to their more human-like endocrine profile. We therefore characterised the initiation of gene transcription in the spiny mouse embryo and compared the pattern of gene expression during the embryonic genome activation (EGA) with common mouse and human embryos. Naturally-mated spiny mouse embryos were obtained at the 2-cell, 4-cell and 8-cell stages of development (n=4 biological replicates per stage). RNA-Seq of these samples produced 709.1M paired-end reads in total. De novo assembly of reads was conducted using Trinity. Embryo-specific transcripts were extracted from the de novo assembly and added to the reference spiny mouse transcriptome. Transcription was first detected between the 2-cell and 4-cell stages for the majority of genes (n=3,428), with fewer genes first transcribed between the 4-cell and 8-cell stages (n=1,150). The pattern of gene expression in spiny mouse embryos during this period of development is more human-like than common mouse embryos. This is the first evidence the spiny mouse may provide a more suitable model of human embryonic development. The improved reference Acomys cahirinus transcriptome is publically accessible, further increasing the value of this tool for ongoing research. Further investigation into early development in the spiny mouse is warranted.

scholarly journals Nucleologenesis and Nucleolotransfer in Mammalian Oocytes: A Review

2017 ◽  
Vol 40 (2) ◽  
pp. 117-124 ◽  
Author(s):  
Michal Benc ◽  
Frantisek Strejcek ◽  
Matej Murin ◽  
Martin Morovic ◽  
Stanislava Martinkova ◽  
...  
Keyword(s):  
Embryonic Development ◽  
Structural Changes ◽  
Regulation Of Transcription ◽  
Cleavage Stage ◽  
Early Cleavage ◽  
Oocyte Growth ◽  
New Information ◽  
Embryonic Genome ◽  
Early Embryos ◽  
Genome Activation

AbstractAn effort to improve development potential of early embryos is one of the main goals of biotechnology in the area of reproductive biology with application in veterinary or human medicine. Recent observations of the function of nucleolus or rather its forms before, during and after the fertilisation or parthenogenetic activation show the key role(s) of nucleolus in the processes of early genome activation. The nucleolus is a subnuclear structure (organelle) mainly involved in regulation of transcription and translation. This organelle has been characterized in detail by immunofluorescence, cell transfection and proteomics. This data was, however, mostly obtained in nucleoli of differentiated eukaryotic cells. Much less is known about the nucleolar structural changes and related functional processes in growing and fully grown mammalian oocytes, zygotes and early cleavage stage embryos, especially in the context of embryonic genome activation. It has been shown, that nucleoli in mammalian oocytes and early embryos have several forms and functions, which vary during the oocyte growth and embryonic development. Certain functions have not been fully described or explained, yet. The method of enucleolation, which allows to remove nucleoli from the oocytes or to exchange nucleoli between oocytes or zygotes, together with their proteomic and structural analyses brought new information about functions of nucleoli in oocytes and early cleavage-stage embryos and allowed to explain some new key roles of nucleoli during oocyte maturation and early embryonic development.

scholarly journals Analysis of active chromatin modifications in early mammalian embryos reveals uncoupling of H2A.Z acetylation and H3K36 trimethylation from embryonic genome activation

Epigenetics ◽  
2012 ◽  
Vol 7 (7) ◽  
pp. 747-757 ◽  
Author(s):  
Ana Bošković ◽  
Ambre Bender ◽  
Laurence Gall ◽  
Celine Ziegler-Birling ◽  
Nathalie Beaujean ◽  
...  
Keyword(s):  
Chromatin Modifications ◽  
Active Chromatin ◽  
Embryonic Genome Activation ◽  
Embryonic Genome ◽  
Mammalian Embryos ◽  
Genome Activation

Cyclin B1 levels in the porcine 4-cell stage embryo

Zygote ◽  
2002 ◽  
Vol 10 (1) ◽  
pp. 79-84 ◽  
Author(s):  
Aaron J. Bonk ◽  
Jon E. Anderson ◽  
Lalantha R. Abeydeera ◽  
Billy N. Day ◽  
Randall S. Prather
Keyword(s):  
Cyclin B1 ◽  
Cell Stage ◽  
Protein Levels ◽  
Cell Cleavage ◽  
Embryonic Genome ◽  
Stage Embryo ◽  
Polymerase Inhibitor ◽  
Genome Activation

The relative quantity of cyclin B1 was determined during the development of in vitro and in vivo derived porcine 4-cell embryos by western blotting and immunolocalised during the 4-cell stage. After cleavage to the 4-cell stage cyclin B1 localised to the cytoplasm at the 5, 10, 18 and 25 time points and localised to the nucleus 33 h post 4-cell cleavage (P4CC). The relative abundance of cyclin B1 was not significantly different in in vivo or in vitro derived 4-cell stage embryos cultured in the absence of the RNA polymerase inhibitor α-amanitin. Cyclin B1 protein was not detectable in embryos cultured in medium without α-amanitin for 5, 10, 18 or 25 h P4CC followed by culture in medium with α-amanitin to 33 P4CC. These results suggest that the maternal to zygotic transition of mRNA production that occurs at the 4-cell stage of the pig embryo does not result in an increase in cyclin B1 production. In addition, cyclin B1 protein levels remained constant in the absence of embryonic genome activation at the 4-cell stage.

scholarly journals Exploring the function of long non-coding RNA in the development of bovine early embryos

2015 ◽  
Vol 27 (1) ◽  
pp. 40 ◽  
Author(s):  
Julieta Caballero ◽  
Isabelle Gilbert ◽  
Eric Fournier ◽  
Dominic Gagné ◽  
Sara Scantland ◽  
...  
Keyword(s):  
Cumulus Cells ◽  
Culture Conditions ◽  
Translation Control ◽  
Functional Characterisation ◽  
Non Coding Rna ◽  
Activation Of Transcription ◽  
Embryonic Genome ◽  
Early Embryos ◽  
Developmental Rates ◽  
Genome Activation

Now recognised as part of the cellular transcriptome, the function of long non-coding (lnc) RNA remains unclear. Previously, we found that some lncRNA molecules in bovine embryos are highly responsive to culture conditions. In view of a recent demonstration that lncRNA may play a role in regulating important functions, such as maintenance of pluripotency, modification of epigenetic marks and activation of transcription, we sought evidence of its involvement in embryogenesis. Among the numerous catalogued lncRNA molecules found in oocytes and early embryos of cattle, three candidates chosen for further characterisation were found unexpectedly in the cytoplasmic compartment rather than in the nucleus. Transcriptomic survey of subcellular fractions found these candidates also associated with polyribosomes and one of them spanning transzonal projections between cumulus cells and the oocyte. Knocking down this transcript in matured oocytes increased developmental rates, leading to larger blastocysts. Transcriptome and methylome analyses of these blastocysts showed concordant data for a subset of four genes, including at least one known to be important for blastocyst survival. Functional characterisation of the roles played by lncRNA in supporting early development remains elusive. Our results suggest that some lncRNAs play a role in translation control of target mRNA. This would be important for managing the maternal reserves within which is embedded the embryonic program, especially before embryonic genome activation.

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