Spatial transcriptomic characterization of a Carnegie stage 7 human embryo.

Gastrulation marks a pivotal stage in mammalian embryonic development, establishing the three germ layers and body axis through lineage diversification and morphogenetic movements. However, studying human gastrulating embryos is challenging due to limited access to early tissues. Here we show the use of spatial transcriptomics to analyse a fully intact Carnegie stage 7 human embryo at single-cell resolution, along with immunofluorescence validations in a second embryo. Employing 82 serial cryosections and Stereo-seq technology, we reconstructed a three-dimensional model of the embryo. Our findings reveal early specification of distinct mesoderm subtypes and the presence of the anterior visceral endoderm. Notably, primordial germ cells were located in the connecting stalk, and haematopoietic stem cell-independent haematopoiesis was observed in the yolk sac. This study advances our understanding of human gastrulation and provides a valuable dataset for future research in early human development.