Person:

Diaz Cuadros, Margarete

Formation of the body of vertebrate embryos proceeds sequentially by posterior addition of tissues from the tail bud. Cells of the tail bud and posterior Presomitic Mesoderm (PSM), which control posterior elongation (1), exhibit a high level of aerobic glycolysis which is reminiscent of the metabolic status of cancer cells experiencing Warburg effect (2, 3). Glycolytic activity downstream of FGF controls Wnt signaling in the tail bud (3). In the Neuro-Mesodermal precursors (NMP) of the tail bud (4), Wnt signaling promotes the mesodermal fate required for sustained axial elongation, at the expense of the neural fate (3, 5). How glycolysis regulates Wnt signaling in the tail bud is currently unknown. Here we used chicken embryos and human tail bud-like cells differentiated in vitro from induced Pluripotent Stem (iPS) cells to show that these cells exhibit an inverted pH gradient, with extracellular pH (pHe) lower than intracellular pH (pHi), as observed in cancer cells (6). Our data suggest that glycolysis increases extrusion of lactate coupled to protons via the monocarboxylate (MCT) symporters. This contributes to elevate the pHi in these cells, creating a favorable chemical environment for non-enzymatic β-catenin acetylation downstream of Wnt signaling. As acetylated β-catenin promotes mesodermal rather than neural fate (7), this ultimately leads to activation of mesodermal transcriptional Wnt targets and specification of the paraxial mesoderm in tail bud precursors. Our work supports the notion that some tumor cells reactivate a developmental metabolic program.

Animals display significant inter-species variation in the rate of embryonic development despite broad conservation of the overall sequence of developmental events. Differences in biochemical reaction speeds, including the rates of protein production and degradation, are thought to be responsible for species-specific rates of development [1-3]. However, the cause of differential biochemical reaction speeds between species remains unknown. Using pluripotent stem cells, we have established an in vitro system that recapitulates the two-fold difference in developmental rate between mouse and human embryos. This system provides a quantitative measure of developmental speed as revealed by the period of the segmentation clock, a molecular oscillator associated with the rhythmic production of vertebral precursors. Using this system, we showed that mass-specific metabolic rates scale with developmental rate and are therefore elevated in mouse cells compared to human cells. We further showed that reducing these metabolic rates by inhibiting the electron transport chain slowed down the segmentation clock by impairing the cellular NAD+/NADH redox balance and, further downstream, lowering the global rate of protein synthesis. Conversely, increasing the NAD+/NADH ratio in human cells by overexpression of the NADH oxidase LbNOX increased translation rate and accelerated the segmentation clock. These findings represent a starting point for the manipulation of developmental rate, with multiple translational applications including the acceleration of human PSCs differentiation for disease modeling and cell-based therapies.