YOHKAICHIYA, T., HOSHIAI, H. and YAJIMA, A. Fibronectin Localization in the Mouse Embryo from the Blastocyst Stage to the Egg Cylinder Stage In Vitro. Tohoku J. exp. Med., 1988, 154 (3), 261-269 - Fibronectin has the characteristics of adhesiveness and cell migration promotion which may play important roles in embryo implantation. Using the direct and indirect immunofluorescence techniques, we found fibronectin on the blastocyst, and the trophoblast cells of the egg cylinder stage embryo, especially at the sites of cell spreading, as well as the inner cell mass. The results show that (i) fibronectin is used for the initial cell attachment to the plastic dish, and (ii) during the course of embryo growth in vitro, the trophoblast cells spread over the plastic dish in the area of cells which contain many granules of fibronectin.