Cross-species single-cell transcriptomic analyses reveal evolutionary conservation and diversification of ovarian tissues

BACKGROUND: The ovary is a central female reproductive organ responsible for producing oocytes and secreting steroid hormones. To investigate the molecular similarities and potential evolutionary origins of the ovary across vertebrates, we integrated publicly available single-cell and single-nucleus transcriptomic data from nine species, including oviparous animals (fish and chicken) and viviparous mammals (mouse, rat, sheep, goat, yak, monkey, and human). RESULTS: We generated a multi-species ovarian atlas comprising 186,748 cells and identified nine cell types. Cross-species comparative analysis identified conserved and species-specific features in granulosa cells (GCs) and stromal cells (SCs), including gene expression patterns, signaling pathways, and cell-cell communication networks. For example, proliferation-associated genes such as CKAP5, MCM3, and GINS1 were shared across vertebrates in GC-3, highlighting the evolutionary conservation of the molecular machinery underlying granulosa cell division. A comparison of granulosa cell subtypes further revealed species-specific gene co-expression patterns in oviparous and viviparous species, indicating adaptations for their different reproductive strategies. Stromal cells showed strong evolutionary conservation, as core extracellular matrix genes (e.g., COL6A1, FSTL1, ACTN1) were co-expressed across species in SC-1. Moreover, the conserved ligand-receptor pairs such as COL4A1-CD44, COL1A1-SDC4, LAMB1-ITGA6-ITGB1, and VEGFA-NRP2 constituted fundamental signaling axes of follicle development, while interactions such as PPIA-BSG in mouse and MDK-NCL in human were higher in these species compared with others, reflecting species-specific ovarian cell communication during evolution. CONCLUSIONS: These findings provide comprehensive insights into the molecular evolution and cellular diversity of the ovary, offering a valuable resource for understanding ovarian biology and evolutionary mechanisms.