MCT1 governs a metabolic checkpoint at pachytene during spermatogenesis

results in a complete arrest at the pachytene stage, characterized by defective homologous recombination, persistent DNA damage, and failure to activate the meiotic transcriptional program. Multi-omic analyses reveal that loss of MCT1 induces a metabolic stress-like state, suppresses expression of key meiotic regulators, and disrupts progression through the pachytene checkpoint. Mechanistically, we demonstrate that MCT1-mediated lactate influx drives histone H4 lysine 12 lactylation (H4K12la) at promoters of meiotic genes, thereby epigenetically licensing their expression. In the absence of MCT1, H4K12la deposition is lost at meiotic loci and redistributed toward stress-response pathways. Together, our findings suggest MCT1-mediated metabolism as an instructive signal that integrates metabolic state with epigenetic regulation to govern meiotic cell-fate progression, defining a previously unrecognized metabolic checkpoint at pachytene.