Recent molecular approaches to elucidate the mechanism of embryo implantation: Trophinin, bystin, and tastin as molecules involved in the initial attachment of blastocysts to the uterus in humans

Elucidation of the implantation mechanism in humans at the molecular level has been difficult because of methodological restrictions. Instead of using human materials during the implantation period, two human tumor cell lines that respectively mimic the biological behaviors of a blastocyst and uteri ne luminal epithelial cells were utilized success fully to identify three n ovel adhesion molecules named trophinin, bystin, and tastin. Trophinin is a membrane protein strongly expressed both on the apical surface of the trop hectoderm of a simian blastocyst and at a putative implantation site of the human endometrium. Bystin and tastin are cytoplasmic proteins that associa te with trophinin by presumably forming an active adhesion machinery The ex pression patterns of these molecules are suggestive of their involvement in the initial blastocyst attachment to the uterus as well as in the subseque nt placental development. Future perspectives in molecular implantation res earch are also discussed in relation to breakthroughs in assisted reproduct ion.