Expression of fibronectin and a fibronectin-binding molecule during preimplantation development in the mouse

Using an indirect immunofluorescent technique, expression ofcell surface fibronectin and a cell surface fibronectin-bindingmolecule was studied during mouse embryo preimplantation development.We also studied the expression of fibronectin on immunosurgicallyisolated inner cell masses (ICMs) and regenerated mouse blastocysts.Fibronectin and the fibronectin-binding molecule were not detectedat the morula stage. From the early to late blastocyst stage,fibronectin expression increased on the trophectoderm. Expressionof the fibronectin-binding molecule was found only in the polartrophectoderm region of the early blastocyst, then in the polarand mural trophectoderm regions of the middle blastocyst. Inthe late blastocyst stage, this fibronectin-binding moleculewas only present in the mural trophectoderm. Fibronectin expressionby ICMs of early blastocysts was more intense than that of lateblastocysts. After 24 h of culture, 10% of ICMs isolated fromearly blastocysts regenerated a trophectoderm which stainedintensively for fibronectin in the mural and polar trophectodermregions. After 48 h of culture, regenerated blastocyst-likestructures closely resembled the normally obtained late blastocystsand stained for fibronectin in the mural and polar trophectodermregions. The significance of the results is discussed in relationto mouse embryo development, trophectoderm formation and blastocystimplantation.