Dynamic remodeling of epithelial junctions in trophoblast cells of the mammalian blastocyst

Proper junction organization within the trophectoderm is essential for blastocyst integrity and implantation. Epithelial junctions are well characterized in many somatic cell types with a typical apical-basal arrangement of junction type: tight junctions, adherens junctions, and then desmosomes. Here, we reveal that the early mural trophoblast of both mouse and human blastocysts exhibit a distinct junction arrangement in which desmosomes are positioned medially within adherens junctions, leaving a basal E-cadherin "tail", which colocalizes with ATP1A1, a marker for Na⁺/K⁺-ATPase pumps. As blastocysts develop and expand approaching hatching and implantation, the organization of junctions in mural trophoblast shifts to the canonical arrangement, and we show that this reorganization requires the ATPase pump function. Together, these data uncover a dynamic remodeling of trophoblast junctions, suggesting a novel connection between junction organization, blastocyst maturation, hatching, and successful implantation.