The contribution of single-cell omics technologies to improve knowledge on human early embryo development

Understanding human early embryo development from fertilization to gastrulation is essential to improve medically assisted reproduction. Faced with technical and ethical limitations, research into peri-implantation stages has been transformed by the recent onset of single-cell omics technologies. These approaches encompassing transcriptomics, epigenomics, and proteomics now enable unprecedented resolution of cellular heterogeneity, lineage specification, and spatial organization during early development. Here, we review the major discoveries permitted by single-cell omics methods, presented chronologically to reflect the progression of embryonic development. We address, among others, the delineation of blastomere contributions, mechanisms of embryonic genome activation, and the sequential specification of the trophectoderm, epiblast, and hypoblast lineages. We also explore how single-cell omics clarifies the effects of aneuploidy, uncovers mural-polar trophectoderm maturation, revises X chromosome regulation, and enables identification of rare post-implantation populations like primordial germ cells and amnion.