Unknown,Transcriptomics,Genomics,Proteomics

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The methyltransferase Setdb1 is essential for meiosis and mitosis in mouse oocytes and early embryo

ABSTRACT: Oocytes develop the competence for meiosis and early embryogenesis during their growth. Setdb1 is a histone H3 lysine 9 (H3K9) methyltransferase required for post-implantation development and has been implicated in the transcriptional silencing of genes and endogenous retroviral elements (ERVs). To address its role in oogenesis and pre-implantation development, we conditionally deleted Setdb1 in growing oocytes. Loss of Setdb1 expression greatly impaired meiosis. It delayed meiotic resumption, altered the dynamics of chromatin condensation, and impaired kinetochore-spindle interactions, bipolar spindle organization, and chromosome segregation in more mature oocytes. The observed phenotypes related to changes in abundance of specific transcripts in mutant oocytes. Setdb1 maternally deficient embryos arrested during pre-implantation development and showed comparable defects during cell cycle progression and in chromosome segregation. Finally, transcriptional profiling data indicate that Setdb1 down-regulates rather than silences expression of ERVK and ERVL-MaLR retrotransposons and associated chimearic transcripts during oogenesis. Our results identify Setdb1 as a novel meiotic and embryonic competence factor in meiosis and mitosis, safeguarding genome integrity at the onset of life. We performed expression profiling on pools of 16 denuded GV-oocytes isolated per mouse. We used oocytes from 4 Setdb1 f/+; Zp3-cre mice and 2 Setdb1 f/- mice as controls and oocytes from 4 Setdb1 f/-; Zp3-cre mice as mutant.

ORGANISM(S): Mus musculus

SUBMITTER: Antoine Peters

PROVIDER: E-GEOD-82002 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Mutation studies always defined the functions of the zona pellucida (ZP) as extracellular, namely: to encase the oocytes in ovarian follicles, to ensure species-specific sperm binding, and to dampen shear stress on the embryo surface. Therefore, mutations in the three ZP mouse genes ZP1, ZP2 or ZP3 cause primary infertility due to empty follicles, polyspermic fertilization or harmful contact between embryos and oviductal epithelium. However, the concepti of ZP2-null and ZP3-null oocytes were still unviable also when the defects were obviated by monospermic fertilization in vitro and blastocyst transfer to uterus (PMID 11245577). This suggests that the tasks of ZPs don’t end in the extracellular space as previously assumed, but there may be also intracellular functions yet to be discovered. The present study tested if experimentally induced degradation of intracellular ZP3 impacted on the development and transcriptome of mouse embryos. To this end we degraded ZP3 using its antibody in conjunction with the ubiquitin-protein ligase TRIM21. This method is known as 'Trim-away' (PMID 29153837). Briefly, in this method a cell (e.g. oocyte) expressing TRIM21 is supplied e.g. injected with a specific antibody to a protein of interest, in this case ZP3. As a result, the ternary complex (target protein-antibody-TRIM21) is destroyed in the proteasome. TRIM21 is here always to be understood as translation product of microinjected mCherry-Trim21 mRNA. We compared two experimental groups, as follows. Pronuclear-stage oocytes (B6C3F1 x CD1) were microinjected with approx. 100 picoliters of mix comprised of mCherry-Trim21 mRNA 0.2 mg/mL + anti-ZP3 antibody (Proteintech 21279-1-AP) 1 mg/mL + dextran beads 0.02 mg/mL, forming a group named 'Trim-away ZP3' group, in triplicate. As a reference, pronuclear-stage oocytes were microinjected with the same mixture as above, except that the antibody buffer was used in lieu of the antibody itself, in triplicate, forming a group named ‚no Trim'. To identify differently expressed genes we compared group 'Trim-away ZP3' with group ‘no Trim’. Ten hours after microinjection, embryos were collected and lysed for transcriptome analysis. Transcriptome analysis revealed that embryos of group 'Trim-away ZP3' and group ‘no Trim' differed in gene expression and were resolved in principal component analysis. The data support a conclusion that ZP3 found inside the embryo was not merely a remnant from oogenesis, but served an intracellular, post-fertilization role during mouse preimplantation development.

Project description:Mutation studies always defined the functions of the zona pellucida (ZP) as extracellular, namely: to encase the oocytes in ovarian follicles, to ensure species-specific sperm binding, and to dampen shear stress on the embryo surface. Therefore, mutations in the three ZP mouse genes ZP1, ZP2 or ZP3 cause primary infertility due to empty follicles, polyspermic fertilization or harmful contact between embryos and oviductal epithelium. However, the concepti of ZP2-null and ZP3-null oocytes were still unviable also when the defects were obviated by monospermic fertilization in vitro and blastocyst transfer to uterus (PMID 11245577). This suggests that the tasks of ZPs don’t end in the extracellular space as previously assumed, but there may be also intracellular functions yet to be discovered. The present study tested if experimentally induced degradation of intracellular ZP3 impacted on the development and transcriptome of mouse embryos. To this end we degraded ZP3 using its antibody in conjunction with the ubiquitin-protein ligase TRIM21. This method is known as 'Trim-away' (PMID 29153837). Briefly, in this method a cell (e.g. oocyte) expressing TRIM21 is supplied e.g. injected with a specific antibody to a protein of interest, in this case ZP3. As a result, the ternary complex (target protein-antibody-TRIM21) is destroyed in the proteasome. TRIM21 is here always to be understood as translation product of microinjected mCherry-Trim21 mRNA. We compared two experimental groups, as follows. Pronuclear-stage oocytes (B6C3F1 x CD1) were microinjected with approx. 100 picoliters of mix comprised of mCherry-Trim21 mRNA 0.2 mg/mL + buffer of ZP3 antibody + dextran beads 0.02 mg/mL as tracer, forming a group named 'Trim21 overexpression', in quadruplicate. As a reference, pronuclear-stage oocytes were microinjected with mCherry-Trim21 mRNA 0.2 mg/mL + anti-ZP3 antibody (Proteintech 21279-1-AP) 1 mg/mL + dextran beads, forming a group named 'Trim-away ZP3' group, in triplicate. To identify differently expressed genes we compared group 'Trim-away ZP3' with group 'Trim21 overexpression'. In addition, a single 'non-manipulated' sample was also incuded merely to confirm that Trim21 was detectable in the two experimental groups, but not in the non-microinjected embryos. On the day after microinjection, embryos were collected and lysed for transcriptome analysis. Those of group 'Trim21 overexpression' were at the 2-cell stage so as the non-manipulated embryos, whereas those of group 'Trim-away ZP3' were arrested at the 1-cell stage. Transcriptome analysis revealed that embryos of group 'Trim-away ZP3' and 'group 'Trim21 overexpression' differed in the expression of 197 of 11137 genes (t test, FDR<0.05). The data support a conclusion that ZP3 found inside the embryo was not merely a remnant from oogenesis, but served an intracellular, post-fertilization role during mouse preimplantation development.

Project description:In mammals, totipotent pre-implantation embryos are formed by fusion of highly differentiated oocytes and spermatozoa. Acquisition of totipotency concurs with remodeling of chromatin states of parental genomes (âepigenetic reprogrammingâ), changes in maternally contributed transcriptome and proteome, and zygotic genome activation. Genomes of mature germ cells are more proficient in supporting embryonic development than those of somatic cells. It is currently unknown whether transgenerational inheritance of chromatin states present in mature gametes underlies the efficacy of early embryonic development after natural conception. Here, we show that Ring1 and Rnf2, two core components of the Polycomb Repressive Complex 1 (PRC1), serve redundant gene regulatory functions during oogenesis that are required to support embryonic development beyond the two-cell stage. Numerous developmental regulatory genes that are established Polycomb targets in various somatic cell types are de-repressed in Ring1/Rnf2 double mutant (dm) fully grown germinal vesicle (GV) oocytes. Translation of tested aberrant maternal transcripts is, however, delayed until after fertilization. Exchange of maternal pro-nuclei between control and Ring1/Rnf2 maternally dm early zygotes demonstrates an essential role for Ring1 and Rnf2 during oogenesis in defining cytoplasmic and nuclear maternal contributions that are both essential for proper initiation of embryonic development. A large number of genes up-regulated in Ring1/Rnf2 dm GV oocytes harbor PRC2-mediated histone H3 lysine 27 trimethylation (H3K27me3) in spermatozoa and in embryonic stem cells (ESCs), and are repressed during normal oogenesis and early embryogenesis. These data strongly support the model that Polycomb acts in the female and male germline to silence differentiation inducing genes and to program chromatin states, thereby sustaining developmental potential across generations. Expression profiling of late 2-cell embryos was performed with the following genotypes: maternal Ring1-Rnf+ (control), maternal Ring1-Rnf2- (maternal Ring1/Rnf2 double mutant). These embryos were obtained by crossing Ring1-/-Rnf2F/F control females or Ring1-/-Rnf2F/F Zp3-cre expreimental females, respectively, to Ring1+/+Rnf2F/F control males. To distinguish between maternal transcripts present in the 2-cell embryo and newly (embryonicaly) transcribed transcripts, embryos from both genotypes were either not treated (expression profiling therefore shows all maternal and embryonic transcripts) or alpha-amanitin treated (alpha-amanitin inhibits de novo transcription, therefore expression profiling of treated embryos will only show maternal transcripts). 11 samples were analyzed: 3 biological replicates (except alpha-amanitin treated maternal Ring1/Rnf2 double mutant, where only 2 replicates were analyzed) of each genotype and treatment group were analyzed. Each sample contains 40 late 2-cell embryos.

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The methyltransferase Setdb1 is essential for meiosis and mitosis in mouse oocytes and early embryo

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