Multiple endocrine neoplasia type 1 (MEN1) is a rare disease caused by mutations in the tumor suppressive gene MEN1. The 3 cardinal lesions are primary hyperparathyroidism, pituitary tumors, and neuroendocrine duodeno-pancreatic tumors. 27 to 70% of MEN1 patients die due to the disease. Despite a very specific phenotype, a large number of sporadic index cases receive a negative or uninformative genetic testing. The identification of mutation is essential to do the diagnosis in patients with an incomplete phenotype, but also to allow genetic counseling in families. Moreover, MEN1 is a long-life treating disease in which the lesions can occurred at any age, with no genotype-phenotype correlation. The disease penetrance is complete, but the phenotypical expression is variable, even within the same family. We reported that patients with MEN1 mosaic mutation have a phenotype as severe as patients with heterozygous mutation Our aim is to improve the diagnosis of MEN1 by developing i) tools to search for unconventional anomalies such as MEN1 mosaicism, promotor and deep-intronic mutation, and ii) functional analysis of sequence variants of uncertain significance. For that, we will use DNA and RNA sequencing of blood samples by next generation sequencing, and we will use a human organoid model of pituitary tumor that we developed in which the VSI will be introduced using Crispr-Cas9. Our second aim is to develop, characterize and compare by using a mosaic disease model, the tumor phenotypes of mouse models with mono- or bi-allelic inactivation of the Men1 gene in neural-crest derived cells at different time points of their pre- and post-natal differentiation. We will study the consequences of MEN1 deficiencies in tissues and the non-cell-autonomous factors that can lead to the development of tumors, in order to better understand the expression variability, and to identify, in very original way, new translational and actionable therapeutic leads.

We will determine the mechanisms of lineage segregation of the cardiopharyngeal mesoderm and investigate defective lineage segregation in syndromes with head and heart defects, with simultaneous lineage and transcriptomic approaches in vivo and in a novel in vitro model. The cardiopharyngeal mesoderm is a cell population that participates in several lineages of the head and heart, with the existence of bi-potent progenitors contributing to muscles of the head and heart. The early steps of cardiopharyngeal mesoderm specification have been poorly explored and a certain number of questions remains to be addressed: Is there a multipotent progenitor that contributes to all cardiopharyngeal mesoderm lineages? When, where and how do cell fate decisions occur? Nobody has investigated precisely what happens during the early steps of cardiopharyngeal specification and how these steps are affected in the velocardiofacial syndrome, a rare congenital disease where both the head and heart are affected. This is however critical to improve the diagnosis and care of patients with these rare diseases. To determine the mechanisms of cardiopharyngeal mesoderm specification in congenital diseases, HEARTIST aims to: 1) Model normal cardiopharyngeal mesoderm lineage segregation, 2) Test cardiopharyngeal mesoderm lineage segregation in syndromic models. HEARTIST will go beyond the state of the art by using simultaneous lineage and transcriptomic approaches in mouse models and in a novel in vitro model of gastrulation derived from mouse embryonic stem cells. HEARTIST is built on solid preliminary results. This ambitious project will enhance our knowledge on cardiopharyngeal mesoderm specification and the mechanisms of congenital diseases that affect multiple organs and improve the diagnosis and care of patients. HEARTIST is built on 2 teams with complementary and solid expertise on cardiopharyngeal mesoderm lineages and gastrulation.

Congenital heart defects affect 1% of live births and have a major impact on mortality and morbidity. The most frequent anomalies affect essential barriers known as septa that separate pulmonary and systemic blood flow within the heart. Despite this clinical imperative, the mechanisms of septum morphogenesis are poorly understood. Insights have come from the realisation that cardiac septa arise at the boundary between early differentiating myocardium of the first heart field (FHF) and cells derived from the second heart field (SHF). New evidence reveals that transient coexpression of FHF and SHF regulators, followed by downregulation of SHF genes, precisely defines the sites of both atrial and ventricular septa. These findings indicate that the heart field interface is a boundary organiser that orchestrates cardiac septation. However, downstream effector genes driving boundary formation and initiating septal morphogenesis have yet to be identified. The overall objective of our project is to uncover how cells at the heart field interface establish a boundary and direct septum morphogenesis. Using in vivo mouse genetic lineage and functional analyses, quantitative imaging, spatial transcriptomics, together with in vitro embryo and gastruloid culture, we will dissect the genetic and cellular events regulating 1) boundary formation at the heart field interface and 2) morphogenesis of the muscular interventricular septum. Our experimental approach builds on new findings that dynamic changes in progenitor cell transcription, including downregulation of Hox gene expression, demarcate septal primordia along a common heart field boundary and that retinoic acid signaling is required for morphogenesis of the muscular ventricular septum, implicating a novel zipper mechanism initiating at the heart field interface. Our results will provide fundamental insights into mechanisms of organogenesis and a new paradigm for understanding the origins of congenital heart defects.

The embryonic heart elongates by addition of epithelial progenitor cells from the second heart field to the growing arterial and venous cardiac poles. Failure of this process results in congenital heart defects. The T-box transcription factors Tbx1 and Tbx5, major genes implicated in 22q11.2 and Holt-Oram Syndrome respectively, demarcate anterior and posterior second heart field subpopulations giving rise to arterial and venous pole myocardium. Recent work has shown that these subdomains originate in a common progenitor population and that differential epithelial cell properties, including adhesion, shape and tension, accompany the segregation of arterial and venous pole progenitor cells. However, how patterning events are coupled to the epithelial properties of the progenitor cell field is unknown. Our project aims to characterise the genetic and cellular mechanisms driving progenitor cell patterning in the epithelial second heart field. We will use mouse genetics, imaging and transcriptomics to define regulatory events upstream and downstream of Tbx1 and Tbx5 and their impact on the epithelial properties of second heart field cells.

Cardiovascular diseases are the leading cause of death in industrialized countries. Cardiac diseases are characterized by cardiomyocyte deficiency and impaired heart function that ultimately leads to congestive heart failure. Conventional treatments do not correct the defects in cardiomyocyte numbers and the prognosis of congestive heart failure remains poor. Specific needs remain for new strategies to enhance cardiac regeneration and to replace cardiomyocytes following injury. Nowadays, the stimulation of terminally differentiated cardiomyocyte proliferation represents the main therapeutic approach for heart regeneration. We recently uncovered that the modulation of the hypoxic and metabolic status of adult cardiomyocytes promotes heart regeneration. The MetabOx-Heart project aims to decipher the interplay between hypoxic and metabolic signaling to induce heart regeneration. This will lead to original and innovative concepts contributing to advances in heart repair and regeneration.