Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(農学) / 甲第19026号 / 農博第2104号 / 新制||農||1030 / 31977 / 京都大学大学院農学研究科応用生物科学専攻 / (主査)教授 今井 裕, 教授 久米 新一, 教授 松井 徹 / 学位規則第4条第1項該当

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第19026号 / 農博第2104号 / 新制||農||1030(附属図書館) / 学位論文||H27||N4908(農学部図書室) / 31977 / 京都大学大学院農学研究科応用生物科学専攻 / (主査)教授 今井 裕, 教授 久米 新一, 教授 松井 徹 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Preimplantation is a short yet critical time period for the embryo that includes dramatic changes in gene expression and developmental potential. During early cleavage, a combination of maternal and zygotic factors program the embryonic genome. These dynamic events result in critical differentiation steps including the first lineage specification (ICM and TE), which is required for implantation. The first half of this thesis investigates the role of Smyd3 as a possible maternal-effect gene, which was identified through an mRNA-based expression assay. Using a Smyd3 conditional allele to remove the function of the protein, we were able to confirm successful allelic recombinations but were unable to confirm the absence of the protein. Due to a lack of a phenotype, two conclusions were made: 1) If we did disrupt Smyd3 function, the lack of a phenotype indicates that Smyd3 is not a maternal-effect gene, and is not required for embryonic viability or adult fertility. 2) It is possible that newly-annotated transcripts are responsible for the necessity of Smyd3, and that the conditional allele used did not disrupt the function of Smyd3. The second half of this thesis uses a reverse genetic RNAi screen that identified Wdr74 as being required for the critical first steps of mammalian development. Knockdown of Wdr74 results in embryos that develop normally until the morula stage but fail to form blastocysts or properly specify the inner cell mass and trophectoderm. In Wdr74-deficient embryos, we find activated Trp53-dependent apoptosis as well as a global reduction of RNA polymerase I, II and III transcripts. In Wdr74-deficient embryos, blocking Trp53 function rescues blastocyst formation and lineage differentiation. These results indicate that Wdr74 is required for RNA transcription, processing and/or stability during preimplantation development and is an essential gene in the mouse.

O arsênio inorgânico, um contaminante ambiental, produz uma série de respostas de estresse em células de mamíferos, incluindo o comprometimento da função mitocondrial, acompanhado por inibição do crescimento celular e carcinogênese. Como previamente identificamos efeitos deletérios do comprometimento da função mitocondrial e dos radicais livres do oxigênio na oogênese, investigamos os efeitos do arsenito na meiose, no desenvolvimento embrionário pré-implantação e na apoptose embrionária em camundongos. Camundongas com 6 semanas de idade foram tratadas com baixa (0,16 mg) ou média dose de arsenito (0,32 mg), por meio de 7 injeções intraperitoneais, 1 a cada 2 dias, durante 14 dias. Os controles foram injetados com solvente. A incidência de anomalias meióticas, caracterizadas por anormalidades do fuso celular e/ou mal alinhamento cromossômico, foi significantemente aumentada tanto nos oócitos in vivo ovulados, como nos in vitro maturados, oriundos dos animais tratados com arsenito. Foram detectadas reduções significativas das taxas de clivagem (24 horas de cultivo), de formação de mórula (72 h) e de desenvolvimento para blastocisto (96 h), nos embriões dos grupos tratados com arsenito. Apesar do número total de núcleos não ter diferido significativamente entre os blastocistos dos grupos controle e de tratamento, a percentagem de núcleos apoptóticos foi significantivamente maior nos blastocistos derivados dos animais tratados com a dose média de arsenito. Estes dados sugerem que o arsenito causa aberrações meióticas, que podem contribuir tanto para o comprometimento do desenvolvimento embrionário pré-implantação, como para a apoptose embrionária. / Inorganic arsenic, an environmental contaminant, produces a variety of stress responses in mammalian cells, including mitochondrial uncoupling accompanied by growth inhibition and carcinogenesis. Because previously we identified detrimental effects of mitochondrial uncoupling, and reactive oxygen species (ROS) on oogenesis, we investigated effects of arsenite on meiosis, early embryo development, and apoptosis in mice. Six-week-old CD-1 mice were treated with either low (0.16mg) or medium (0.32mg) doses of arsenite every two days by 7 intraperitoneal injections for 14 days, and controls were injected with solvent. The incidence of meiotic anomalies, characterized by spindle disruption and/or chromosomal misalignment or spreading, was significantly increased in both in vivo and in vitro treated oocytes. Further, we found a significant decrease in cleavage rates at 24h, morula formation at 72h, and development to blastocyst at 96h in treated groups. Although the total number of nuclei in developed blastocysts did not significantly differ between the treated and control groups, the percentage of apoptotic nuclei was significantly increased in blastocysts derived from the medium dose treated group. These data suggest that arsenite causes meiotic aberrations, which may contribute to decreased cleavage and preimplantation development, as well as increased apoptosis.

O arsênio inorgânico, um contaminante ambiental, produz uma série de respostas de estresse em células de mamíferos, incluindo o comprometimento da função mitocondrial, acompanhado por inibição do crescimento celular e carcinogênese. Como previamente identificamos efeitos deletérios do comprometimento da função mitocondrial e dos radicais livres do oxigênio na oogênese, investigamos os efeitos do arsenito na meiose, no desenvolvimento embrionário pré-implantação e na apoptose embrionária em camundongos. Camundongas com 6 semanas de idade foram tratadas com baixa (0,16 mg) ou média dose de arsenito (0,32 mg), por meio de 7 injeções intraperitoneais, 1 a cada 2 dias, durante 14 dias. Os controles foram injetados com solvente. A incidência de anomalias meióticas, caracterizadas por anormalidades do fuso celular e/ou mal alinhamento cromossômico, foi significantemente aumentada tanto nos oócitos in vivo ovulados, como nos in vitro maturados, oriundos dos animais tratados com arsenito. Foram detectadas reduções significativas das taxas de clivagem (24 horas de cultivo), de formação de mórula (72 h) e de desenvolvimento para blastocisto (96 h), nos embriões dos grupos tratados com arsenito. Apesar do número total de núcleos não ter diferido significativamente entre os blastocistos dos grupos controle e de tratamento, a percentagem de núcleos apoptóticos foi significantivamente maior nos blastocistos derivados dos animais tratados com a dose média de arsenito. Estes dados sugerem que o arsenito causa aberrações meióticas, que podem contribuir tanto para o comprometimento do desenvolvimento embrionário pré-implantação, como para a apoptose embrionária. / Inorganic arsenic, an environmental contaminant, produces a variety of stress responses in mammalian cells, including mitochondrial uncoupling accompanied by growth inhibition and carcinogenesis. Because previously we identified detrimental effects of mitochondrial uncoupling, and reactive oxygen species (ROS) on oogenesis, we investigated effects of arsenite on meiosis, early embryo development, and apoptosis in mice. Six-week-old CD-1 mice were treated with either low (0.16mg) or medium (0.32mg) doses of arsenite every two days by 7 intraperitoneal injections for 14 days, and controls were injected with solvent. The incidence of meiotic anomalies, characterized by spindle disruption and/or chromosomal misalignment or spreading, was significantly increased in both in vivo and in vitro treated oocytes. Further, we found a significant decrease in cleavage rates at 24h, morula formation at 72h, and development to blastocyst at 96h in treated groups. Although the total number of nuclei in developed blastocysts did not significantly differ between the treated and control groups, the percentage of apoptotic nuclei was significantly increased in blastocysts derived from the medium dose treated group. These data suggest that arsenite causes meiotic aberrations, which may contribute to decreased cleavage and preimplantation development, as well as increased apoptosis.

La chromatine embryonnaire subit des changements nécessaires pour l’établissement d’un nouveau programme développemental. Ce travail a étudié l’organisation de l’hétérochromatine au cours du développement sous trois facettes. La première étant celle de d’hétérochromatine constitutive, à travers, l’établissement forcé de la marque H4K20me3 qui provoque un arrêt du développement préimplantatoire. Ce phénotype dépend spécifiquement de l’activité de la methyltransferase SUV4-20h2 et induit l’activation de la voie de signalisation ATR qui bloque la phase de réplication. En deuxième partie, l’hétérochromatine facultative a été le sujet d’une analyse de l’expression des protéines du complexe non-canonique PRC1 et de la modification H2AK119ub qui en résulte. Finalement, une analyse de la chromatine embryonnaire a été mise en place et a permis la détection des changements de niveau de compaction au cours du développement préimplantatoire. / Embryonic chromatin undergoes necessary changes to establish a new developmental program. This work has addressed the organization of heterochromatin in preimplantation embryos from three angles. The first part probed the absence of constitutive heterochromatin by forcing the establishment of the H4K20me3 mark which results in an embryonic arrest prior to the 2-cell stage. This phenotype is due to the specific histone methyl-transferase activity of SUV4-20h2 and is induced by ATR activation which blocks replication. In the second part, facultative heterochromatin was studied by analyzing the levels of several members of the non-canonical PRC1 complex as well as the resultant modification H2AK119ub. Finally, an analysis of the embryonic chromatin was set up and allowed for the measurement of changes in the chromatin openness during preimplantation development.

Les marqueurs épigénétiques, en particulier la méthylation de l’ADN des gènes soumis à empreinte parentale, sont sensibles aux changements environnementaux. Les techniques de l’aide médicalisée à la procréation (AMP) nécessitant la manipulation des gamètes et des embryons in vitro et dans la plupart des cas la stimulation hormonale de l’ovulation des patientes, peuvent interférer avec la reprogrammation et/ou le maintien de la méthylation des gènes soumis à empreinte. Afin d’évaluer ce risque nous avons analysé le profil de méthylation de KvDMR1, qui régule l’expression de KCNQ1OT1, dans des ovocytes humains mûris in vivo ou in vitro, provenant de patientes stimulées ou non. Nos résultats montrent que la mise en place de la méthylation au niveau de KvDMR1 se poursuit au cours de la maturation de l’ovocyte après reprise de la méiose, in vivo et in vitro et que la superovulation des patientes en AMP génère des ovocytes épigénétiquement immatures. Par ailleurs, l’étude de la méthylation de KvDMR1 et de H19 DMR (qui régule l’expression d’Igf2 et H19) dans des embryons issus d’ICSI, évolutifs ou présentant un défaut de développement, n’établit pas de lien entre les dérégulations de l’empreinte et l’arrêt du développement embryonnaire au stade blastocyste. / Epigenetic modifications, particularly DNA methylation of imprinted genes are sensible to environment. Techniques of assisted reproduction require in vitro manipulation of gamete and embryos and currently superovulation of patients. These technologies may interfere with eprogramming and maintenance of methylation at imprinted genes. To evaluate such a risk, we have determined the methylation profile of KvDMR1, the region that regulates KCNQ1OT1 imprinted gene, in human oocytes retrieved from stimulated or unstimulated cycles, at different phases of their maturation in vivo or in vitro. Our results show that the timing of establishment of the methylation profile of KvDMR1 covers the maturation phase of 199 oocyte growth, in vivo and in vitro, and that hyperstimulation likely recruits young follicles epigenetically immature. Analysis of the methylation profile of KvDMR1 and H19DMR (DMR of IGF2/H19) in ICSI embryos suggests that imprinting disorders are not responsible of embryo developmental failure prior the blastocyst stage

No description available.

Les techniques d’assistance médicale à la procréation particulièrement l’induction de l’ovulation, la maturation in vitro des ovocytes et la culture embryonnaire prolongée impliquent la manipulation des gamètes ainsi que les embryons à des moments critiques de leur maturation et développement qui sont également des étapes clé du remodelage épigénétique. Par conséquent, elles pourraient interférer avec la reprogrammation épigénétique, en particulier la mise en place de la méthylation des gènes soumis a empreinte au cours de l'ovogenèse, ou son maintien au cours du développement préimplantatoire. Afin d’évaluer ce risque nous avons analysé le profil de méthylation de KvDMR1, qui régule l’expression de KCNQ1OT1, dans des ovocytes humains mûris in vivo ou in vitro, provenant de patientes stimulées ou non. Nos résultats montrent que la mise en place de la méthylation au niveau de KvDMR1 se poursuit au cours de la maturation de l’ovocyte du stade VG au stade MII, in vivo et in vitro et que l’induction ovarienne des patientes génère des ovocytes épigénétiquement immatures. Par ailleurs, l’étude de la méthylation de H19 DMR qui régule l’expression d’Igf2 et H19 dans des embryons d’ICSI, atypiques bloqués en culture prolongée et dans les spermes correspondants met en évidence une hypométhylation de l'allèle paternel et une méthylation de l'allèle maternel dans certains embryons, sans que l'on puisse établir de lien entre les dérégulations de l’empreinte et l’arrêt du développement au stade blastocyste. / Assisted reproductive technologies particularly the induction of ovulation, oocytes in vitro maturation, and prolonged embryo culture require in vitro manipulation of gamete and embryos at critical times of their maturation and development. In consequence, they may interfere with epigenetic reprogramming and affect particularly demethylation and remethylation of imprinted genes. To evaluate such a risk, we have determined the methylation profile of KvDMR1, the region that regulates KCNQ1OT1 imprinted gene, in human oocytes retrieved from stimulated or unstimulated cycles, at different phases of their maturation in vivo or in vitro. Our results show that the timing of establishment of the methylation profile of KvDMR1 covers the maturation phase of oocyte growth, in vivo and in vitro, and that hyperstimulation likely recruits young follicles epigenetically immature. Analysis of the methylation profile of H19DMR (DMR of IGF2/H19) in atypical ICSI embryos and corresponding sperm suggests that imprinting disorders are not responsible of embryo developmental failure prior the blastocyst stage.