Morphological features of the interaction between the im¬ planting blastocyst and the uterine endometrium were studied by electron microscopy, using material fixed in situ. The observations extended from the pre-attachment stage to the completion of tropho¬ blastic erosion of the uterine epithelium and early decidual transforma¬ tion of the stromal cells.After shedding of the zona pellucida, the blastocyst establishes contact with the tips of microvilli and with bleb-like cytoplasmic protrusions of the epithelial cells. Attachment occurred during the afternoon of the 5th day post coitum (p.c.). Patches of'bristle-coated' membrane appeared on the trophoblast membrane at that time. A lattice-like substructure was discernible in the cytoplasmic plaques, which are abundant in the early blastocyst. Sperm-tail inclusions were observed in both trophoblast and inner cell mass as late as Day 5 p.c.By the 6th day p.c., the epithelial microvilli were usually lost and the trophoblast membrane interlocked with that of the epithelial cells, with frequent formation of tight junctions. Leucocytes were occasionally seen in the epithelial layer at the attachment site. Unusually electron-dense cells were often found wedged between the trophoblast and epithelial cells; their possible relation to Wilson bodies is discussed.The earliest morphological response of the stromal cells to blastocyst attachment was the appearance of changes in nuclear shape, chromatin distribution and nucleolar structure in the subepithelial layer. The deeper subepithelial stroma became oedematous, and diapedesis, erythro-phagocytosis and later the formation of sinusoids could be observed.

Progesterone pretreatment (5 mg/day) of ovariectomized\p=m-\ adrenalectomized rats for at least 12 hr abolished the response of the uterine luminal epithelium to oestradiol (0\m=.\2\g=m\g) with respect to (i) mitotic activity, (ii) nucleolar enlargement, and (iii) [3H]uridine uptake, and suppressed the uptake of [3H]oestradiol by the epithelial cells, as judged by dry-mount autoradiography. Progesterone pretreatment for periods exceeding 36 hr redirected the

Trophinin is a membrane protein that mediates apical cell adhesion between trophoblastic cells and luminal epithelial cells of the endometrium and is implicated in the initial attachment during the process of human embryo implantation. The present study identified novel trophinin gene transcripts, which encode proteins structurally distinct from trophinin protein in the mouse. We designated these proteins "magphinins," because they share consensus amino acid sequences with MAGE (melanoma-associated antigen) superfamily proteins. Among many MAGE proteins, magphinins are closely related to NRAGE, which mediates p75 neurotrophin receptor-dependent apoptosis, and necdin, which is a strong suppressor of cell proliferation in post-mitotic neurons. There are three major forms of magphinins, i.e. magphinin-␣, -␤, and -␥, in the mouse, which are formed due to alternative usage of different exons. Northern blot analysis revealed that magphinins are expressed in brain, ovary, testis, and epididymis. In addition, Western blot analysis and in vitro translation experiments showed that magphinins expressed in the mouse ovary and testis are translation products utilizing the second initiation AUG codon and contain an active nuclear localization signal. Ectopic expression of magphinins in mammalian cells resulted in nuclear localization of magphinin and suppressed cell proliferation. Immunohistochemistry of the mouse ovary and testis showed that magphinin proteins are distributed in the cytoplasm of the male and female germ cells, whereas these proteins are translocated to the nucleus at a specific stage of gametogenesis. These results strongly suggest that magphinins regulate cell proliferation during gametogenesis in the mouse.Mammals retain distinctions with regard to the strategies used to protect and nourish their offspring during development, namely by the process of embryo implantation and placentation. The process of implantation varies markedly between species (1), and genes involved in this process display remarkably high spontaneous mutational rates (2), suggesting a strong adaptive selection pressure. The study of human embryo implantation at the molecular level is hampered by the fact that in vivo studies with an implanting embryo in place are difficult to perform and are generally considered ethically unacceptable. To overcome this problem, we established an in vitro cell culture system using two human cell lines, trophoblastic teratocarcinoma HT-H and endometrial adenocarcinoma SNG-M. These two cell types adhered with each other at their respective apical cell membranes and exhibited morphologies resembling the cells at the initial adhesion steps of embryo implantation (3, 4).Using this model system, we identified a unique protein, trophinin, by means of expression cloning. Thus a mammalian expression cDNA library constructed from HT-H cells was transfected into COS cells, and COS cells that became adhesive to SNG-M cells were selected. When COS cells acquired trophinin and trophinin-associated cytoplasmic protein...

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