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, Slc2a1 and Slc2a3 both of which co-express with the expression of both the mesodermal marker T/Bra and the neural marker Sox2. 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 of T/Bra without affecting the expression of Sox2 and 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 of T/Bra expression in gastruloids.