Evolutionarily divergent transcriptomic programs in ovarian folliculogenesis across mice, monkeys and humans

Understanding the mechanisms for human ovarian folliculogenesis is fundamental to reproductive biology and medicine. Here, we investigated transcriptomic dynamics in individual oocytes and their associated granulosa cells (GCs) during folliculogenesis in mice, monkeys and humans. Unlike mouse oocytes, which exhibited stage-specific, stepwise transcriptomic maturation, monkey and human oocytes showed minimal transcriptomic changes until the secondary follicle stage and could be broadly categorized as either immature or mature. In all three species, most highly variable genes during oocyte growth displayed monotonic up- or downregulation, with limited overlap in highly variable genes across species. GCs exhibited similarly species-specific transcriptomic trajectories. Correspondingly, intercellular communication pathways, including ligand-receptor signaling, gap junctions, and metabolic coupling between oocytes and GCs, demonstrated substantial species-specific differences. Nonetheless, X-chromosome dosage compensation and repression of evolutionarily young transposons were conserved across species. We established in vitro culture systems supporting preantral to antral follicle development in monkeys and humans, revealing relatively normal oocyte transcriptome maturation but aberrant GC profiles. By delineating interspecies differences in folliculogenesis, this study provides a framework for understanding human ovarian development and advancing its in vitro reconstruction.