Cross-species insights into placental evolution and diseases at the single-cell resolution.

The placenta is essential for fetal development, yet its molecular evolution across mammals remains elusive. Here, we present a comprehensive single-cell transcriptomic atlas of ~300,000 cells from ten species representing the four primary placental types: discoid, cotyledonary, diffuse, and zonary. Our cross-species analysis identifies trophoblast lineages as the primary drivers of placental diversification. By reconstructing differentiation trajectories, we elucidate the regulatory networks shaping trophoblast development across diverse architectures. We propose that the unique gene expression profile of human trophoblasts underlies the susceptibility to preeclampsia and miscarriage. Functional experiments demonstrate that TGIF1 acts as a key upstream regulator of extravillous trophoblast growth and migration. TGIF1 and its targets, including ADAM12, WNT3A, and ZNF831, are associated with preeclampsia and pregnancy loss. Collectively, this high-resolution framework provides fundamental insights into the molecular evolution of the placenta and its contribution to reproductive success and diseases.