Contribution de H2AK119Ub1 dérivée du spermatozoïde au développement embryonnaire précoce du Xénope

Deposition of H2AK119Ub1 by the Polycomb repressive complex plays a key role in the formation of facultative heterochromatin in somatic cells. Here, we assess the contribution of sperm H2AK119Ub1 to embryonic gene expression. In Xenopus laevis, we found that H2AK119Ub1 is conserved during spermiogenesis and early embryonic development, highlighting its credential for a role in transmitting epigenetic information from sperm to embryo. Sperm treated with USP21, an H2A deubiquitylase, just prior to injection into the egg, results in developmental abnormalities. RNA-Seq analyzes in the corresponding embryos demonstrated dysregulation of gene expression after treatment with USP21. ChIP-Seq analyzes revealed an enrichment of the H2AK119Ub1/H3K4me3 bivalent configuration on the regulatory regions of genes sensitive to USP21. Finally, a complementary quantitative ChIP-Seq study indicates that during sperm chromatin replication, H2AK119Ub1 is preferentially retained on regions associated with genes sensitive to USP21, in a context where most of H2AK119Ub1 is diluted. We conclude that the transmission to the embryo of sperm derived H2AK119Ub1 is required for proper early embryonic development and the repression of certain embryonic genes.La déposition de H2AK119Ub1 par le complexe répressif Polycomb joue un rôle clé dans la formation de l’hétérochromatine facultative dans les cellules somatiques. Ici, nous évaluons la contribution de la marque H2AK119Ub1 du spermatozoïde sur l'expression des gènes embryonnaires. Chez Xenopus laevis, nous avons constaté que H2AK119Ub1 est conservé pendant la spermiogenèse et au début du développement embryonnaire, soulignant son potentiel pour un rôle dans la transmission d’informations épigénétiques du spermatozoïde à l'embryon. Le spermatozoïde traité avec USP21, une deubiquitylase H2A, juste avant l'injection dans l'oeuf, entraîne des anomalies du développement. Des analyses RNA-Seq dans les embryons correspondants ont démontré une dérégulation de l’expression génique après traitement par USP21. Des analyses ChIP-Seq ont permis de mettre en évidence un enrichissement de la configuration H2AK119Ub1/H3K4me3 sur les régions régulatrices des gènes sensibles à l'USP21. Enfin, une étude ChIP-Seq quantitative complémentaire indique que lors de la réplication de la chromatine du spermatozoïde, H2AK119Ub1 est retenue préférentiellement sur les régions associées aux gènes sensibles à USP21, dans un contexte où la majeure partie de H2AK119Ub1 est diluée. Nous concluons que la transmission à l’embryon de H2AK119Ub1 dérivée du spermatozoïde est requise pour un bon déroulement du développement embryonnaire précoce et la répression de certains gènes embryonnaires

Study of sperm epigenetic contribution for the regulation of embryonic gene transcription in early development

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The limit of cell specification concept: a lesson from scRNA-Seq on early human development

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NOTO Transcription Factor Directs Human Induced Pluripotent Stem Cell-Derived Mesendoderm Progenitors to a Notochordal Fate

International audienceThe founder cells of the Nucleus pulposus, the centre of the intervertebral disc, originate in the embryonic notochord. After birth, mature notochordal cells (NC) are identified as key regulators of disc homeostasis. Better understanding of their biology has great potential in delaying the onset of disc degeneration or as a regenerative-cell source for disc repair. Using human pluripotent stem cells, we developed a two-step method to generate a stable NC-like population with a distinct molecular signature. Time-course analysis of lineage-specific markers shows that WNT pathway activation and transfection of the notochord-related transcription factor NOTO are sufficient to induce high levels of mesendoderm progenitors and favour their commitment toward the notochordal lineage instead of paraxial and lateral mesodermal or endodermal lineages. This study results in the identification of NOTO-regulated genes including some that are found expressed in human healthy disc tissue and highlights NOTO function in coordinating the gene network to human notochord differentiation

Integrated pseudotime analysis of human pre-implantation embryo single-cell transcriptomes reveals the dynamics of lineage specification

Understanding lineage specification during human pre-implantation development is a gateway to improving assisted reproductive technologies and stem cell research. Here we employ pseudotime analysis of single-cell RNA sequencing (scRNA-seq) data to reconstruct early mouse and human embryo development. Using time-lapse imaging of annotated embryos, we provide an integrated, ordered, and continuous analysis of transcriptomics changes throughout human development. We reveal that human trophectoderm/inner cell mass transcriptomes diverge at the transition from the B2 to the B3 blastocyst stage, just before blastocyst expansion. We explore the dynamics of the fate markers IFI16 and GATA4 and show that they gradually become mutually exclusive upon establishment of epiblast and primitive endoderm fates, respectively. We also provide evidence that NR2F2 marks trophectoderm maturation, initiating from the polar side, and subsequently spreads to all cells after implantation. Our study pinpoints the precise timing of lineage specification events in the human embryo and identifies transcriptomics hallmarks and cell fate markers

Induction of human trophoblast stem cells from somatic cells and pluripotent stem cells

International audienceHuman trophoblast stem cells (hTSCs) derived from blastocysts and first-trimester cytotrophoblasts offer an unprecedented opportunity to study the placenta. However, access to human embryos and first-trimester placentas is limited, thus preventing the establishment of hTSCs from diverse genetic backgrounds associated with placental disorders. Here, we show that hTSCs can be generated from numerous genetic backgrounds using post-natal cells via two alternative methods: (1) somatic cell reprogramming of adult fibroblasts with OCT4, SOX2, KLF4, MYC (OSKM) and (2) cell fate conversion of naive and extended pluripotent stem cells. The resulting induced/converted hTSCs recapitulated hallmarks of hTSCs including long-term self-renewal, expression of specific transcription factors, transcriptomic signature, and the potential to differentiate into syncytiotrophoblast and extravillous trophoblast cells. We also clarified the developmental stage of hTSCs and show that these cells resemble day 8 cytotrophoblasts. Altogether, hTSC lines of diverse genetic origins open the possibility to model both placental development and diseases in a dish