Somatic cells compartmentalise their carbohydrate metabolism to sustain germ cell survival.

To ensure success in reproduction, organisms dedicate substantial resources to supporting the germline. In testes, somatic gonadal cells form a barrier that isolates germ cells from circulating nutrients, raising the question of how germ cell metabolism is sustained and how somatic cells ensure that sufficient resources are directed to the germline. Here, we use lineage-specific genetic manipulations and metabolite reporters to show that Drosophila somatic gonadal cells break down circulating sugars to produce and shuttle lactate to germ cells in vivo, thus sustaining their survival. Further, we uncover that somatic cells ensure the allocation of carbohydrate metabolites specifically to germ cell support and that increasing autonomous consumption of carbohydrates in somatic cells increases germ cell death. Thus, germ cell survival depends on functional metabolic compartmentalisation within gonadal somatic support cells.