Séminaire de l’Institut Jacques Monod – Olivier Pourquié

Invité par l’équipe Ribes/Nedelec, Olivier Pourquié (Frank Burr Mallory Professor of Pathology, Brigham and Women’s Hospital; Professor of Genetics, Harvard Medical School) présentera un séminaire de l’Institut Jacques Monod sur le thème :

Deconstructing human musculo-skeletal development in vitro 

Résumé :

Skeletal muscles and vertebrae derive from precursors located in the embryonic segments called somites. These structures form periodically from a posterior tissue called Presomitic Mesoderm (PSM). The rhythmic formation of somites involves a molecular oscillator called segmentation clock which drives pulses of Notch, Wnt and FGF signaling in the PSM. Virtually nothing is known on human somitogenesis as it proceeds between 3- and 5-weeks post conception when embryos are extremely difficult to access. We have developed protocols to differentiate human pluripotent stem cells (ES/iPS) in vitro into PSM. Single cell RNA-sequencing comparison of these human cells differentiating in vitro with mouse embryo PSM reveals that they faithfully recapitulate the PSM differentiation sequence in vitro. Using our in vitro system as a proxy for human somitogenesis, we were able to demonstrate that human iPS reporter cells harboring a HES7 fluorescent reporter differentiated to PSM exhibit 5-hour oscillations, thus identifying the human segmentation clock. We have also succeeded in generating PSM organoids that can sequentially form somites exhibiting a normal antero-posterior pattern in vitro. We have taken advantage of these in vitro systems to perform experiments otherwise unfeasible in model organisms. We have generated a human iPS cell line lacking all HOX clusters and demonstrated that while it differentiates to the paraxial mesoderm fate, it is unable to generate somites. By mimicking key signaling events leading to muscle formation in the embryo, we developed directed differentiation protocols which recapitulate the developmental sequence of myogenesis. We then used these cells to generate new in vitro models of Duchenne Muscular Dystrophy and to pioneer the production of human satellite cells for cell therapy strategies for muscular dystrophies. Our work provides a framework to study early stages of human myogenesis which are poorly accessible in the embryo.