Abstract
Embryo implantation is a complex process consisting of multiple cross-talks between
maternal and embryonic cells. Defining the mechanisms underlying implantation at molecular
level is challenging task in reproductive biology. In order to identify molecules
involved in cellular interactions between trophoblastic and endometrial epithelial
cells, we have established two human cell lines, trophoblastic HT-H and endometrial
epithelial SNGM. These two cell types exhibit cell adhesion at their respective apical
cell membranes. Molecules involved in this unique cell adhesion were identified by
expression complementary DNA cloning and were named trophinin, tastin, and bystin.
Trophinin is a membrane protein thought to have self-binding activity and thus mediates
homophilic cell adhesion. Tastin and bystin are cytoplasmic proteins required for
trophinin to exhibit cell adhesion activity. Trophinin is strongly expressed in trophectoderm
of monkey blastocysts. In human endometrium, trophinin is expressed for a limited
period in the luminal epithelium at the time expected for implantation. In human placenta,
trophinin, tastin, and bystin are strongly expressed in trophoblast and endometrium
at the uteroplacental interface at an early stage in pregnancy. All these molecules
disappear from the human placenta in the second trimester. The unique expression pattern
and cell adhesion activity exhibited by trophinin, tastin, and bystin suggest strongly
the involvement of these molecules in the initial attachment of blastocyst to uterus.
Keywords:
Trophinin - tastin - bystin - implantation - cloning
