Blastocyst cells forming extraembryonic structures:
Blastocyst differentiation yields two lineages: inner cell mass pluripotent and outer trophoblast. Trophoblast cells after compaction express Cdx2 driven by nuclear YAP-TEAD activity where Hippo pathway inactive. These cells proliferate to form cytotrophoblast and syncytiotrophoblast contributing to placenta, chorion, and implantation invasion secreting hCG and facilitating uterine interface. Inner cell mass generates embryo proper, not extraembryonic placenta. Polar bodies degenerate, zona pellucida is extracellular coat shed before implantation. Therefore trophoblast represents exclusive progenitor of extraembryonic supportive structures required for maternal-fetal exchange, immune tolerance and endocrine support during pregnancy development progression.
Ref: Posfai et al., Dev Biol 2021: Trophectoderm lineage specification and placental derivatives of blastocyst.