Mannose is crucial for mesoderm specification and symmetry breaking in gastruloids
Patterning and growth are fundamental features of embryonic development that must be tightly coordinated during morphogenesis. As metabolism can control cell growth while also providing mechanistic links to developmental signalling pathways, it is ideally placed to enable this coordination. To understand how metabolism impacts early mesoderm specification, we used mouse embryonic stem (ES) cell-derived gastruloids, as these enable temporal control over metabolic manipulations and can be generated in large quantities. Gastruloids show mosaic expression of two glucose transporters,Slc2a1andSlc2a3both of which co-express with the expression of both the mesodermal markerT/Braand the neural markerSox2. To understand the significance of cellular glucose uptake in development, we used the glucose metabolism inhibitor 2-deoxy-D-glucose (2-DG). 2-DG specifically blocks the expression ofT/Brawithout affecting the expression ofSox2and abolishes axial elongation in gastruloids. Surprisingly, removing glucose completely from the medium did not phenocopy 2-DG treatment despite a significant decline in glycolytic intermediates occurring under both conditions. As 2-DG can also act as a competitive inhibitor of mannose, we added mannose together with 2-DG and found that it could rescue the mesoderm specification. Together, our results show that while mannose is crucial for mesoderm specification, the glycolytic pathway is dispensable at early stages ofT/Braexpression in gastruloids. Overall design: We treated gastruloids with 5mM of a glucose metabolism inhibitor 2-Deoxy-D-Glucose (2-DG), 0mM and 63.75 mM (3X) of glucose between day 3-4 of gastruloid development and compared the transcriptome of these treatments with that of the control i.e.gastruloids  treated with 21.25mM (1X) Glucose.