Glycogen and lactate metabolism in mouse fetal Sertoli cells sustain the germ line

Metabolites are key regulators of cell fate decisions, chromatin remodeling, and lineage commitment. While genetic pathways governing testis differentiation are well studied, the role of metabolism remains poorly understood. In this study, we investigate the transient, male-specific accumulation of glycogen in supporting cells of the fetal testis in mice, between embryonic days 11.5 and 13.5. Blocking glycogen metabolism/accumulation in vivo and in vitro is dispensable for Sertoli cell differentiation. However, its disruption leads to reduced lactate production and reduced germ cell number in the testis. Inhibiting lactate transport reveals a critical metabolic coupling between Sertoli and germ cells during early testis development. Surprisingly, external lactate or glucose supplementation fails to rescue the germ cell phenotype. These findings suggest that glycogen accumulation supports a critical developmental window in which both Sertoli and germ cells are metabolically constrained and unable to rely on external carbon sources.