A three-dimensional human co-culture system reveals reciprocal embryo-endometrial adaptation at implantation onset.

Co-culture of human blastoids or natural blastocysts with decidualized endometrial stromal cells induces trophoblast subsets marked by SDC1 + MMP7 + that emerge at implantation-like progression.

• Why it matters: Early trophoblast–endometrial interface dynamics at implantation onset are poorly resolved in vivo, limiting mechanistic understanding of reciprocal embryo–endometrial adaptation.
• What they did: Using an endometrial assembloid-based three-dimensional co-culture system, the study applied time-series single-cell transcriptomics plus functional perturbation across independent implantation-like systems.
• The result: The SDC1 + MMP7 + trophoblast subsets are reproducibly detected in decidualized stromal co-culture, linked to stromal-derived CSF3 signalling, while endometrium shows enhanced decidualization and glandular hypersecretory transition.