Project Summary/Abstract The proposed project is focused on the crosstalk between metabolism and cell fate during development of the paraxial mesoderm, the tissue which forms skeletal muscles and vertebrae. One striking characteristic of this tissue is its segmentation into repeated structures termed somites, a process driven by a molecular oscillator called segmentation clock [1]. Defects in paraxial mesoderm development can lead to severe malformations such as congenital scoliosis, spina bifida or caudal agenesis. The paraxial mesoderm arises from a population of progenitors located in the primitive streak and tail bud. Remarkably, these progenitor cells exhibit aerobic glycolysis and an inverted intra- vs. extracellular pH gradient, which are characteristic of the Warburg effect of cancer cells [2, 3]. In the tailbud, we demonstrated that glycolysis increases the intracellular pH to promote acetylation of -catenin and Wnt activation, which ultimately leads to paraxial mesoderm induction [3]. As these processes are difficult to study in vivo, we have developed in vitro systems in which embryonic stem (ES) cells or induced pluripotent stem (iPS) cells can be efficiently differentiated toward the paraxial mesoderm fate recapitulating the normal features of its metabolism, signaling and even oscillations of the segmentation clock [4-7]. We will now take advantage of these in vitro systems, as well as mouse and chicken embryos, to characterize in detail the role of aerobic glycolysis in paraxial mesoderm development to see how it relates to the Warburg effect. In this application, we propose to carry out large scale multi-omics experiments (metabolomics, transcriptomics, proteomics, epigenomics) and live imaging of cellular metabolic state to characterize the impact of metabolic transitions on the regulation of gene expression, protein function and cell fate. As the physiological significance of the Warburg effect is not well understood, carefully dissecting its role in the embryo might help shed light on its role in cancer. Finally, we propose to use in vivo, ex vivo and in vitro systems recapitulating the oscillations of the segmentation clock to study the role of metabolism in the control of the oscillatory period. We will analyze the differences in metabolism regulation between mouse and human paraxial mesoderm cells, with special focus on mitochondrial respiration. The period of the oscillations diverges significantly between the two species and can be used as a proxy for developmental timing to try to understand why human development proceeds more slowly than mouse development. We expect these experiments to shed light on the molecular basis of developmental timing, which is tightly linked to longevity in mammals.