Development of the anterior-posterior axis is a self-organizing process in the absence of maternal cues in the mouse embryo.

This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/cr.2015.104This work was supported by Wellcome Trust, Grant ID: 098287 (MZG) and EMBO (MB)

Embryo size regulates the timing and mechanism of pluripotent tissue morphogenesis.

Mammalian embryogenesis is a paradigm of regulative development as mouse embryos show plasticity in the regulation of cell fate, cell number, and tissue morphogenesis. However, the mechanisms behind embryo plasticity remain largely unknown. Here, we determine how mouse embryos respond to an increase in cell numbers to regulate the timing and mechanism of embryonic morphogenesis, leading to the formation of the pro-amniotic cavity. Using embryos and embryonic stem cell aggregates of different size, we show that while pro-amniotic cavity formation in normal-sized embryos is achieved through basement membrane-induced polarization and exocytosis, cavity formation of increased-size embryos is delayed and achieved through apoptosis of cells that lack contact with the basement membrane. Importantly, blocking apoptosis, both genetically and pharmacologically, alters pro-amniotic cavity formation but does not affect size regulation in enlarged embryos. We conclude that the regulation of embryonic size and morphogenesis, albeit concomitant, have distinct molecular underpinnings

Embryo Size Regulates the Timing and Mechanism of Pluripotent Tissue Morphogenesis

Mammalian embryogenesis is a paradigm of regulative development as mouse embryos show plasticity in the regulation of cell fate, cell number, and tissue morphogenesis. However, the mechanisms behind embryo plasticity remain largely unknown. Here, we determine how mouse embryos respond to an increase in cell numbers to regulate the timing and mechanism of embryonic morphogenesis, leading to the formation of the pro-amniotic cavity. Using embryos and embryonic stem cell aggregates of different size, we show that while pro-amniotic cavity formation in normal-sized embryos is achieved through basement membrane-induced polarization and exocytosis, cavity formation of increased-size embryos is delayed and achieved through apoptosis of cells that lack contact with the basement membrane. Importantly, blocking apoptosis, both genetically and pharmacologically, alters pro-amniotic cavity formation but does not affect size regulation in enlarged embryos. We conclude that the regulation of embryonic size and morphogenesis, albeit concomitant, have distinct molecular underpinnings

Epigenetic remodelling licences adult cholangiocytes for organoid formation and liver regeneration.

Following severe or chronic liver injury, adult ductal cells (cholangiocytes) contribute to regeneration by restoring both hepatocytes and cholangiocytes. We recently showed that ductal cells clonally expand as self-renewing liver organoids that retain their differentiation capacity into both hepatocytes and ductal cells. However, the molecular mechanisms by which adult ductal-committed cells acquire cellular plasticity, initiate organoids and regenerate the damaged tissue remain largely unknown. Here, we describe that ductal cells undergo a transient, genome-wide, remodelling of their transcriptome and epigenome during organoid initiation and in vivo following tissue damage. TET1-mediated hydroxymethylation licences differentiated ductal cells to initiate organoids and activate the regenerative programme through the transcriptional regulation of stem-cell genes and regenerative pathways including the YAP-Hippo signalling. Our results argue in favour of the remodelling of genomic methylome/hydroxymethylome landscapes as a general mechanism by which differentiated cells exit a committed state in response to tissue damage.RCUK Cancer Research UK ERC H2020 Wellcome Trus

Modelling thyroid embryogenesis using embryonic stem cells

Congenital hypothyroidism (CH) is the most frequent of the rare endocrine diseases (e.g. Addison's disease, Cushing's syndrome, Congenital adrenal hyperplasia.), which affects 1:2000 – 4000 newborns. If not immediately diagnosed after birth, thyroid hormones deficiency causes severe defects in brain and skeletal development leading to a complex clinical scenario called cretinism. CH can be due to a defective synthesis of thyroid hormones (dyshormonogenesis) or an abnormal embryonic development of the gland. Data obtained using knockout mouse models have shown the pivotal role of four specific transcription factors (NKX2.1, PAX8, FOXE1 and HHEX) for the correct organogenesis or function of the gland. Although mutations in those genes have been identified in few cases of CH patients, the pathogenetic mechanisms remain still elusive in the vast majority of CH cases (95%).For the identification of new genes and molecular events controlling thyroid organogenesis it would be useful to develop an in vitro cellular model to recapitulate thyroid embryogenesis in a dish. Embryonic Stem Cells (ESCs) have recently emerged as system model to recapitulate the embryogenesis of several tissues in vitro.Induced overexpression of defined transcription factors has been shown to have a directing effect on the differentiation of pluripotent stem cells into specific cell types. In this thesis I show that a transient overexpression of the transcription factors NKX2.1 and PAX8 is sufficient to direct the differentiation of murine ESCs into thyroid follicular cells (TFC) and promotes in vitro self- assembly of TFC into three-dimensional follicular structures, when associated to a subsequent thyrotropin (TSH) treatment. Cells differentiated by this protocol showed significant iodide organification activity, a hallmark of thyroid tissue function. Importantly, athyroid mice grafted with mESC-derived thyroid follicles show normalization of plasma T4 levels with concomitant decrease of plasma TSH. In addition, a full normalization of body temperature at 4 weeks after transplantation was observed. Together, these data clearly demonstrate that grafting of our mESC-derived thyroid cells rescues the hypothyroid state and triggers symptomatic recovery along with the normalization of plasma hormone concentrations. The high efficiency of TFC differentiation and follicle morphogenesis in our system will provide an unprecedented opportunity for future studies to decipher regulatory mechanisms involved in embryonic thyroid development, a major research need towards an improved understanding of the molecular mechanisms underlying congenital hypothyroidism, the most common congenital endocrine disorder in humans.Doctorat en Sciences biomédicales et pharmaceutiquesinfo:eu-repo/semantics/nonPublishe

Concerted cell divisions in embryonic visceral endoderm guide anterior visceral endoderm migration.

Migration of Anterior Visceral Endoderm (AVE) is a critical symmetry breaking event in the early post-implantation embryo development and is essential for establishing the correct body plan. Despite much effort, cellular and molecular events influencing AVE migration are only partially understood. Here, using time-lapse live imaging of mouse embryos, we demonstrate that cell division in the embryonic visceral endoderm is coordinated with AVE migration. Moreover, we demonstrate that temporal inhibition of FGF signalling during the pre-implantation specification of embryonic visceral endoderm perturbs cell cycle progression, thus affecting AVE migration. These findings demonstrate that coordinated cell cycle progression during the implantation stages of development is important for post-implantation morphogenesis in the mouse embryo

Generation of Functional Thyroid Tissue Using 3D-Based Culture of Embryonic Stem Cells.

During the last decade three-dimensional (3D) cultures of pluripotent stem cells have been intensively used to understand morphogenesis and molecular signaling important for the embryonic development of many tissues. In addition, pluripotent stem cells have been shown to be a valid tool for the in vitro modeling of several congenital or chronic human diseases, opening new possibilities to study their physiopathology without using animal models. Even more interestingly, 3D culture has proved to be a powerful and versatile tool to successfully generate functional tissues ex vivo. Using similar approaches, we here describe a protocol for the generation of functional thyroid tissue using mouse embryonic stem cells and give all the details and references for its characterization and analysis both in vitro and in vivo. This model is a valid approach to study the expression and the function of genes involved in the correct morphogenesis of thyroid gland, to elucidate the mechanisms of production and secretion of thyroid hormones and to test anti-thyroid drugs.info:eu-repo/semantics/publishe

Modeling Brain Tumors: A Perspective Overview of in vivo and Organoid Models

Brain tumors are a large and heterogeneous group of neoplasms that affect the central nervous system and include some of the deadliest cancers. Almost all the conventional and new treatments fail to hinder tumoral growth of the most malignant brain tumors. This is due to multiple factors, such as intra-tumor heterogeneity, the microenvironmental properties of the human brain, and the lack of reliable models to test new therapies. Therefore, creating faithful models for each tumor and discovering tailored treatments pose great challenges in the fight against brain cancer. Over the years, different types of models have been generated, and, in this review, we investigated the advantages and disadvantages of the models currently use