Maternally inherited rRNA triggers de novo nucleolus formation in porcine embryos

SummaryThe present study examines the role of RNA polymerase I (RPI)-mediated transcription, maternally inherited rRNA and nucleolar proteins in the resumption of fibrillogranular nucleoli during embryonic genome activation (EGA) in porcine embryos. Late 4-cell embryos were incubated in the absence (control) or presence of actinomycin D (AD) (0.2 μg/ml for inhibition of RPI; 2.0 μg/ml for inhibition of total transcription) and late 2-cell embryos were cultured to the late 4-cell stage with 0.2 μg/ml AD to block EGA. Embryos were then processed for reverse-transcriptase polymerase chain reaction (RT-PCR), and for autoradiography (ARG), transmission electron microscopy (TEM), fluorescence in situ hybridization (FISH), silver staining and immunofluorescence (for RPI). Embryos in the control group displayed extranucleolar and intranucleolar ARG labelling, and exhibited de novo synthesis of rRNA and reticulated functional nucleoli. Nucleolar proteins were located in large foci. After RPI inhibition, nucleolar precursors transformed into segregated fibrillogranular structures, however no fibrillar centres were observed. The localization of rDNA and clusters of rRNA were detected in 57.1% immunoprecipitated (IP) analyzed nucleoli and dispersed RPI; 30.5% of nuclei showed large deposits of nucleolar proteins. Embryos from the AD-2.0 group did not display any transcriptional activity. Nucleolar formation was completely blocked, however 39.4% of nuclei showed rRNA clusters; 85.7% of nuclei were co-localized with nucleolar proteins. Long-term transcriptional inhibition resulted in the lack of ARG and RPI labelling; 40% of analyzed nuclei displayed the accumulation of rRNA molecules into large foci. In conclusion, maternally inherited rRNA co-localized with rDNA and nucleolar proteins can initiate a partial nucleolar assembly, resulting in the formation of fibrilogranular structures independently on activation of RPI-mediated transcription.

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5 NUCLEOLAR DEVELOPMENT REQUIRES TRANSCRIPTIONAL ACTIVITY DURING PORCINE EMBRYONIC GENOME ACTIVATION

Reproduction Fertility and Development ◽

10.1071/rdv19n1ab5 ◽

2007 ◽

Vol 19 (1) ◽

pp. 120 ◽

Cited By ~ 3

Author(s):

O. Svarcova ◽

P. Maddox-Hyttel ◽

H. Niemann ◽

D. Hermann ◽

Z. Rasmussen ◽

...

Keyword(s):

Rna Polymerase ◽

Transcriptional Activity ◽

De Novo ◽

Large Fish ◽

Rt Pcr ◽

Cell Stage ◽

Transcriptional Inhibition ◽

Nucleolar Proteins ◽

Embryonic Genome ◽

Genome Activation

The development of a functional nucleolus accompanying the major embryonic genome activation (EGA) is considered a marker for embryo quality and viability. However, the use of this marker is limited by the lack of accurate knowledge of the biology of embryonic nucleologenesis. The objective of this study was to elucidate the role of RNA polymerase I (RPI) and total transcriptional activity, reflecting EGA, for nucleologenesis in in vivo-developed porcine embryos. Late 4-cell-stage embryos were cultured in the absence (control) or presence of actinomycin D (AD; 0.2 �g mL-1, 3 h for RPI inhibition; 2.0 �g mL-1, 3 h for total transcriptional inhibition). Late 2-cell-stage embryos were cultured to the late 4-cell stage with 0.2 �g mL-1 AD (long-term inhibition) to prevent EGA. Embryos were fixed at the late 4-cell stage and processed for RT-PCR (de novo synthesized rRNA), autoradiography (ARG, following culture with 3H-uridine for the last 20 min before fixation), TEM, FISH (probe-labeling rRNA and rDNA), silver staining of nucleolar proteins, and immunofluorescence for RPI. Control embryos displayed typical extranucleolar and nucleolar ARG labeling, fibrillo-granular nucleoli, and focal RPI localization signaling de novo rRNA synthesis in functional nucleoli, confirmed by RT-PCR. All nuclei showed large FISH clusters (rRNA and rDNA) that in 88% of the cases were co-localized with large foci of silver-stained nucleolar proteins. After RPI inhibition, only extranucleolar ARG labeling was detected and, instead of fibrillo-granular nucleoli, a segregated dense-fibrillar component and a granular component, but no fibrillar centers, were observed. RPI was dispersed in all nuclei, the number of nuclei presenting large FISH clusters decreased to 40%, and only 42% of nuclei showed nucleolar proteins localized to large foci. After total transcriptional inhibition and long-term inhibition, the nuclei did not display any ARG labeling and presented inactive nucleolus precursor bodies indicating lack of rRNA (RT-PCR) and total RNA synthesis. However, 40% of the nuclei in both groups presented large FISH clusters of rRNA. This rRNA is considered as partially processed residues of maternally inherited molecules, and their clustering is most likely independent of EGA. Inhibition of transcriptional activity at the time of EGA caused the dispersion of RPI (de novo synthesized) but did not influence the localization of silver-stained nucleolar proteins to large foci (41%). On the other hand, EGA inhibition caused the lack of RPI labeling and hampered the localization of nucleolar proteins to foci. Differences between these 2 groups could be due to the activation of RNA polymerase II before the 3-h AD treatment. In conclusion, RPI transcription and de novo protein synthesis are required for formation of functional nucleoli. However, the clustering of maternally inherited nucleolar transcripts is independent on transcriptional activity at the time of EGA. Failure in constituent RNA polymerase activation during EGA leads to pattern-specific changes in nucleologenesis, which may serve as a marker for early embryo quality.

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Mouse oocytes nucleoli rescue embryonic development of porcine enucleolated oocytes

Zygote ◽

10.1017/s0967199417000491 ◽

2017 ◽

Vol 25 (6) ◽

pp. 675-685 ◽

Cited By ~ 4

Author(s):

Martin Morovic ◽

Frantisek Strejcek ◽

Shoma Nakagawa ◽

Rahul S. Deshmukh ◽

Matej Murin ◽

...

Keyword(s):

Embryonic Development ◽

De Novo ◽

Blastocyst Stage ◽

Rrna Synthesis ◽

Control Group ◽

Cell Stage ◽

Nucleolar Proteins ◽

Transmission Electron ◽

Binding Factor ◽

Upstream Binding Factor

SummaryIt is well known that nucleoli of fully grown mammalian oocytes are indispensable for embryonic development. Therefore, the embryos originated from previously enucleolated (ENL) oocytes undergo only one or two cleavages and then their development ceases. In our study the interspecies (mouse/pig) nucleolus transferred embryos (NuTE) were produced and their embryonic development was analyzed by autoradiography, transmission electron microscopy (TEM) and immunofluorescence (C23 and upstream binding factor (UBF)). Our results show that the re-injection of isolated oocyte nucleoli, either from the pig (P + P) or mouse (P + M), into previously enucleolated and subsequently matured porcine oocytes rescues their development after parthenogenetic activation and some of these develop up to the blastocyst stage (P + P, 11.8%; P + M, 13.5%). In nucleolus re-injected 8-cell and blastocyst stage embryos the number of nucleoli labeled with C23 in P + P and P + M groups was lower than in control (non-manipulated) group. UBF was localized in small foci within the nucleoli of blastocysts in control and P + P embryos, however, in P + M embryos the labeling was evenly distributed in the nucleoplasm. The TEM and autoradiographic evaluations showed the formation of functional nucleoli and de novo rRNA synthesis at the 8-cell stage in both, control and P + P group. In the P + M group the formation of comparable nucleoli was delayed. In conclusion, our results indicate that the mouse nucleolus can rescue embryonic development of enucleolated porcine oocytes, but the localization of selected nucleolar proteins, the timing of transcription activation and the formation of the functional nucleoli in NuTE compared with control group show evident aberrations.

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Formation of nucleoli in interspecies nuclear transfer embryos derived from bovine, porcine, and rabbit oocytes and nuclear donor cells of various species

Reproduction ◽

10.1530/rep-10-0266 ◽

2011 ◽

Vol 141 (4) ◽

pp. 453-465 ◽

Cited By ~ 21

Author(s):

Irina Lagutina ◽

Valeri Zakhartchenko ◽

Helena Fulka ◽

Silvia Colleoni ◽

Eckhard Wolf ◽

...

Keyword(s):

Nuclear Transfer ◽

De Novo ◽

Mammalian Species ◽

Housekeeping Genes ◽

Cell Stage ◽

Whole Process ◽

Embryonic Genome ◽

Donor Nucleus ◽

Donor Cells ◽

Genome Activation

The most successful development of interspecies somatic cell nuclear transfer (iSCNT) embryos has been achieved in closely related species. The analyses of embryonic gene activity in iSCNT embryos of different species combinations have revealed the existence of significant aberrations in expression of housekeeping genes and genes dependent on the major embryonic genome activation (EGA). However, there are many studies with successful blastocyst (BL) development of iSCNT embryos derived from donor cells and oocytes of animal species with distant taxonomical relations (inter-family/inter-class) that should indicate proper EGA at least in terms of RNA polymerase I activation, nucleoli formation, and activation of genes engaged in morula and BL formation. We investigated the ability of bovine, porcine, and rabbit oocytes to activate embryonic nucleoli formation in the nuclei of somatic cells of different mammalian species. In iSCNT embryos, nucleoli precursor bodies originate from the oocyte, while most proteins engaged in the formation of mature nucleoli should be transcribed from genes de novo in the donor nucleus at the time of EGA. Thus, the success of nucleoli formation depends on species compatibility of many components of this complex process. We demonstrate that the time and cell stage of nucleoli formation are under the control of recipient ooplasm. Oocytes of the studied species possess different abilities to support nucleoli formation. Formation of nucleoli, which is a complex but small part of the whole process of EGA, is essential but not absolutely sufficient for the development of iSCNT embryos to the morula and BL stages.

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61 REVERSIBLE INHIBITION OF BOVINE MINOR EMBRYONIC GENOME ACTIVATION IMPAIRS PRE-IMPLANTATION DEVELOPMENT

Reproduction Fertility and Development ◽

10.1071/rdv29n1ab61 ◽

2017 ◽

Vol 29 (1) ◽

pp. 138

Author(s):

R. P. Nociti ◽

R. V. Sampaio ◽

V. F. M. H. de Lima ◽

R. M. Schultz ◽

P. J. Ross

Keyword(s):

Rna Polymerase ◽

Rna Polymerase Ii ◽

Reversible Inhibitor ◽

Blastocyst Formation ◽

Cell Stage ◽

Developmental Potential ◽

Embryonic Genome Activation ◽

Transcriptional Inhibition ◽

Embryonic Genome ◽

Genome Activation

Bovine pre-implantation embryos can develop in the absence of gene expression up to the 8/16-cell stage, the time when the major embryonic genome activation (EGA) occurs. Some embryonic genes, however, are transcribed before EGA (minor EGA). This study used a reversible inhibitor of RNA Polymerase II (5,6 dichlorobenzimidazole 1-β-D-ribofuranoside; DRB) to assess the importance of minor EGA for development to the blastocyst stage. Oocytes were matured and inseminated in vitro, and the fertilized eggs were cultured in supplemented KSOMaa and allocated to different treatments 16 h post-insemination (hpi). Development was recorded at 44 and 72 hpi, and the incidence of blastocyst formation on Day 7 (IVF = Day 0) was recorded. Data were analysed by ANOVA followed by Duncan test. First, we tested different DRB concentrations [50 μM (D50), 75 μM (D75), 100 μM (D100), and dimethyl sulfoxide vehicle control (CTRL)] to block development to blastocyst when continuously present. Only embryos in CTRL produced blastocysts (45.0 ± 5.8%; 4 replicates with a total of 391 oocytes examined). No difference in development was observed at 44 h (57.9 ± 16.5, 53.3 ± 10.5, 60.5 ± 19.0, and 52.3 ± 5.8% for D50, D75, D100, and CTRL, respectively) and 72 h (78.9 ± 8.8, 66.1 ± 11.7, 71.5 ± 16.5, and 70.8 ± 5.6% for D50, D75, D100, and CTRL, respectively). Next, in 7 replicates (751 oocytes) we determined the effect of blocking transcription (50 μM DRB) spanning 2 embryo stages (periods of 28 h), initiated at 16 hpi (1&2C), 30 hpi (2&4C), and 44 hpi (4&8C). Controls included DRB treatment from 16 to 72 hpi (1–8C) and CTRL. There was no difference in development at 44 and 72 h. The incidence of blastocyst formation, however, was significantly decreased in all treatment groups compared with CTRL (27.7 ± 4.7; 15.1 ± 3.5; 23.3 ± 3.1; 20.5 ± 1.9; and 42.1 ± 3.2% for 1&2C, 2&4C, 4&8C, 1–8C, and CTRL, respectively). Finally, in 12 replicates (1499 oocytes), the effect of blocking transcription for 14-h periods, spanning mostly a unique cleavage stage, was evaluated. The DRB treatment (50 μM) started at 16 hpi (1C), 30 hpi (2C), 44 hpi (4C), and 58 hpi (8C). Furthermore, 1–16C and CTRL treatments were included. No difference in development at 44 and 72 h were observed. Development to the blastocyst was significantly lower from CTRL (46.0 ± 3.2%) in 2C, 4C, 8C, and 1–16C (28.9 ± 3.9, 26.1 ± 4.2, 30.1 ± 4.8, and 18.9 ± 3.2%, respectively) but not in 1C (34.7 ± 4.4%). In summary, continuous transcriptional inhibition using DRB resulted in a developmental block at the time of major EGA, similar to α-amanitin treatment (an irreversible RNA Polymerase II inhibitor). Transcriptional inhibition during single cleavage stages was sufficient to decrease the developmental potential of the embryo. We conclude that minor EGA has an important role for bovine development. This work was funded by NIH-NICHD R01HD070044 to P. J. Ross. R. P. Nociti was sponsored by CNPQ; R. V. Sampaio was sponsored by FAPESP.

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The role of RNA-polymerase II transcription in embryonic nucleologenesis by bovine embryos

Biologia ◽

10.2478/s11756-010-0046-2 ◽

2010 ◽

Vol 65 (3) ◽

Author(s):

Mária Kovalská ◽

Ida Petrovičová ◽

František Strejček ◽

Marian Adamkov ◽

Erika Halašová ◽

...

Keyword(s):

Rna Polymerase ◽

Rna Polymerase Ii ◽

De Novo ◽

Control Group ◽

Bovine Embryos ◽

Embryonic Genome Activation ◽

Embryonic Genome ◽

Autoradiographic Labeling ◽

Genome Activation

AbstractThe early stages of embryonic development are maternally driven. As development proceeds, maternally inherited informational molecules decay, and embryogenesis becomes dependent on de novo synthesized RNAs of embryonic genome. The aim of the present study is to investigate the role of de novo transcription in the development of embryos during embryonic genome activation. Autoradiography for detection of transcriptional activity and transmission electron microscopy were applied in in vitro produced bovine embryos cultured to the late 8-cell stage with or without (control group) α-amanitin, specific inhibitor of RNA-polymerases II and III transcription. The α-amanitin (AA) groups presented three sets of embryos cultivated with AA in different time intervals (6, 9 and 12 h). In control group, nucleoplasm and nucleolar structures displayed strong autoradiographic labeling and showed initial development of fibrillo-granular nucleoli. In α-amanitin groups, lack of autoradiographic labeling and disintegrated nucleolus precursor bodies (NPBs) stage were observed. Inhibition of RNA polymerase II (RNA pol II) already in the early phases of embryonic genome activation has detrimental effect on nucleolar formation and embryo survival, what was shown for the first time.

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The embryonic nucleologenesis during inhibition of major transcriptional activity in bovine preimplantation embryos

Biologia ◽

10.2478/s11756-012-0066-1 ◽

2012 ◽

Vol 67 (4) ◽

Author(s):

Mária Kovalská ◽

Marián Hruška-Plocháň ◽

Oľga Østrup ◽

Marian Adamkov ◽

Ján Lehotský ◽

...

Keyword(s):

Messenger Rna ◽

Actinomycin D ◽

De Novo ◽

Specific Inhibitor ◽

Preimplantation Embryos ◽

Control Group ◽

Cell Stage ◽

Initial Development ◽

Embryonic Genome ◽

Autoradiographic Labeling

AbstractCommon features of embryonic genome activation in mammalian and non-mammalian embryos are the colocalization of pre-assembled complexes of maternally inherited nucleolar proteins, the so-called nucleolus precursor bodies and de novo synthesized transcripts with ribosomal DNA. The de novo transcription of messenger RNA and ribosomal RNA proteins is required for the development of functional nuclei during the major activation of the embryonic genome. The aim of our work was to investigate to what extent. Autoradiography and transmission electron microscopy has been applied in in vitro produced bovine embryos. The embryos were cultured to the late 8-cell stage with: α-amanitin; a specific inhibitor of RNA-polymerases II and III transcription; actinomycin D; a specific inhibitor of RNA polymerase I transcription; and without inhibitors (control group). Nucleoplasm and nucleolar structures displayed strong autoradiographic labeling and showed the initial development of fibrillo-granular nucleoli in the control group. In α-amanitin groups, however, in both inhibited groups of embryos, lack of autoradiographic labeling and disintegrated nucleolus precursor bodies stage were observed. Our study of α-amanitin as well as in actinomycin D groups proves inhibition of transformation nucleolus precursor bodies to active nucleoli. From our results follows, actinomycin D is able to penetrate through zona pellucida, what was shown for the first time.

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Expression of the HSP 70.1 gene, a landmark of early zygotic activity in the mouse embryo, is restricted to the first burst of transcription

Development ◽

10.1242/dev.121.1.113 ◽

1995 ◽

Vol 121 (1) ◽

pp. 113-122 ◽

Cited By ~ 4

Author(s):

E. Christians ◽

E. Campion ◽

E.M. Thompson ◽

J.P. Renard

Keyword(s):

Dna Replication ◽

Mouse Embryo ◽

Culture Conditions ◽

Hsp 70 ◽

Cell Stage ◽

Embryonic Genome ◽

Genome Activation ◽

Alpha Amanitin ◽

Zygotic Genome

Activation of the mouse embryonic genome at the 2-cell stage is characterized by the synthesis of several alpha-amanitin-sensitive polypeptides, some of which belong to the multigenic hsp 70 family. In the present work we show that a member of this family, the HSP 70.1 gene, is highly transcribed at the onset of zygotic genome activation. Transcription of this gene began as early as the 1-cell stage. Expression of the gene continued through the early 2-cell stage but was repressed before the completion of the second round of DNA replication. During this period we observed that the level of transcription was modulated by in vitro culture conditions. The coincidence of repression of HSP70.1 transcription with the second round of DNA replication was not found for other transcription-dependent polypeptides synthesized at the 2-cell stage.

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Human embryonic genome activation initiates at the one-cell stage

Cell Stem Cell ◽

10.1016/j.stem.2021.11.012 ◽

2021 ◽

Author(s):

Maki Asami ◽

Brian Y.H. Lam ◽

Marcella K. Ma ◽

Kara Rainbow ◽

Stefanie Braun ◽

...

Keyword(s):

Cell Stage ◽

Embryonic Genome Activation ◽

Embryonic Genome ◽

The One ◽

Genome Activation

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Early cleavage to formation of the unilaminar blastocyst in the marsupial Antechinus stuartii: ultrastructure

Reproduction Fertility and Development ◽

10.1071/r96049 ◽

1997 ◽

Vol 9 (2) ◽

pp. 201 ◽

Cited By ~ 9

Author(s):

Henry Sathananthan ◽

Lynne Selwood ◽

Isabel Douglas ◽

Kamani Nanayakkara

Keyword(s):

Smooth Endoplasmic Reticulum ◽

Spindle Pole ◽

Blastocyst Stage ◽

Cell Junctions ◽

Cell Stage ◽

Transmission Electron ◽

Embryonic Genome ◽

Antechinus Stuartii ◽

First Time

The development of Antechinus stuartiifrom the 2-cell stage to the blastocyst stage in vivo was examined by routine transmission electron microscopy. The 2–8-cell stages had a similar organization of organelles, whereas the 16- to 32-cell stages had pluriblast cells and trophoblast cells forming an epithelium closely apposed to the zona pellucida. Specialized cell–zona plugs were formed at the 8-cell stage, and primitive cell junctions appeared in later conceptuses. The cytoplasmic organelles included mitochondria, lysosomes, aggregates of smooth endoplasmic reticulum, lipid and protein yolk bodies and fibrillar arrays, possibly contractile in function. Nuclei had uniformly-dispersed dense chromatin. Nucleoli of 2–4-cell conceptuses were dense, compact and fibrillar, and those of 8-cell conceptuses and later conceptuses were finely granular and became progressively reticulated. The embryonic genome is probably not switched on before the 8-cell stage. Sperm tails were detected in cells in several early conceptuses. The yolk mass had the same organelles as cells. Centrioles were discovered for the first time in marsupial conceptuses. These were prominently situated at a spindle pole in a 32-cell blastomere and were associated with a nucleus and sperm tail at the 4-cell stage. It is very likely that the paternal centrosome is inherited at fertilization and perpetuated in Antechinus embryos during cleavage.

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69 GLOBAL H3k9ac AND H3k27me3 EXPRESSION IN BLASTOMERES FROM 8- TO 16-CELL STAGE BOVINE EMBRYOS

Reproduction Fertility and Development ◽

10.1071/rdv26n1ab69 ◽

2014 ◽

Vol 26 (1) ◽

pp. 148

Author(s):

C. S. Oliveira ◽

N. Z. Saraiva ◽

L. Z. Oliveira ◽

R. V. Serapião ◽

M. R. de Lima ◽

...

Keyword(s):

Monoclonal Antibody ◽

Histone Modifications ◽

Pearson Correlation ◽

Developmental Competence ◽

Bovine Embryos ◽

Cell Stage ◽

Embryonic Genome Activation ◽

Embryonic Genome ◽

Group A ◽

Genome Activation

Embryonic genome activation is a crucial step in early embryo development, and is accompanied by a dramatic change in the epigenetic profile of blastomeres. Histone modifications related to euchromatin and heterochromatin can be important parameters to infer developmental competence, as they are affected by manipulation and environmental stress conditions. The aim of this study was to characterise permissive (H3k9ac) and repressive (H3k27me3) histone modifications during the embryonic genome activation cell cycle in bovine embryos, regarding correlation between those marks and variance among blastomeres. For that, bovine embryos were produced by IVF and cultured in SOF medium supplemented with 5 mg mL–1 of BSA and 2.5% FCS in 5% O2 in an air atmosphere for 5 days (70 h after IVF). The 8 to 16 cell embryos were fixed in 4% paraformaldehyde and submitted to H3k9ac and H3k27me3 immunofluorescence assay (mouse anti-H3K9ac monoclonal antibody, 1 : 200; Sigma; rabbit anti-H3k27me3 monoclonal antibody, 1 : 200; Upstate, Charlottesville, VA, USA). Nuclei were counterstained with Hoechst 33342. Images of each embryo were captured (AxioCam, Carl Zeiss, São Paulo, Brazil) and measured for nuclear fluorescence intensity in each blastomere using Adobe Photoshop CS3 (Adobe Systems, San Jose, CA, USA). Mean levels were compared using the Mann-Whitney test and variances were compared using F-test (SAS 9.1, SAS Institute Inc., Cary, NC, USA; P = 0.05). We evaluated 2 replicates and 12 embryos during the transition from the 8 to 16 cell stages, totaling 169 blastomeres. Global H3k27me3 levels varied accordingly to H3k9ac levels, as indicated by a high Pearson correlation coefficient (r = 0.913). Levels of each blastomere were normalized to the lowest level obtained within each embryo. Some embryos displayed a high variation between blastomeres, and, for further analysis, we divided the embryos into groups: group A for embryos that presented similar H3k9ac levels between blastomeres (8 embryos, 66%), and group B for embryos that exhibited higher heterogeneity between blastomeres (at least 2 blastomeres presenting a 2-fold increase compared to the lowest blastomere; 4 embryos, 33%). Mean H3k9ac and H3k27me3 normalized levels were lower for group A [H3k9ac: 1.35 ± 0.29 (A), 1.94 ± 1.02* (B); H3k27me3: 1.33 ± 0.24 (A), 1.99 ± 0.77 (B)], and group A displayed lower variance values (H3k9ac: 0.07 (A), 1.05* (B); H3k27me3: 0.06 (A), 0.60 (B)]. Within each embryo, blastomeres were sorted in ascending order for H3k9ac level (1 to 16), and compared between groups A and B. We detected that mean levels differed (P < 0.05) between groups from blastomere 9 to 16 for H3k9ac and 10 to 16 for H3k27me3. Therefore, in 8- to 16-cell stage embryos, the H3k27me3 repressive mark is highly correlated with the H3k9ac permissive mark. Also, our results describe the presence of 2 distinguishable populations of bovine embryos at this stage, considering their epigenetic status. One population presented similar levels of repressive and permissive marks among blastomeres, whereas the second one displayed a remarkable variation among their blastomeres. This observation should be further studied, as it might reflect distinct cleavage pattern embryos and blastomere competence. The authors acknowledge FAPESP, FAPERJ and CNPq for financial support.

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