The amnion is a critical extra-embryonic structure that supports foetal development, yet its ontogeny remains poorly defined. Here, using single-cell transcriptomics, we identified major cell types and subtypes in the human amnion across the first trimester of pregnancy, broadly categorized into epithelial, mesenchymal and macrophage lineages. We uncovered epithelial–mesenchymal and epithelial–immune transitions, highlighting dynamic remodelling during early pregnancy. Our results further revealed key intercellular communication pathways, including BMP4 signalling from mesenchymal to epithelial cells and TGF-β signalling from macrophages to mesenchymal cells, suggesting coordinated interactions that drive amnion morphogenesis. In addition, integrative comparisons across humans, non-human primates and in vitro stem cell-based models reveal that stem cell-based models recapitulate various stages of amnion development, emphasizing the need for careful selection of model systems to accurately recapitulate in vivo amnion formation. Collectively, our findings provide a detailed view of amnion cellular composition and interactions, advancing our understanding of its developmental role and regenerative potential.
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