The effect of hexapeptides on attachment and outgrowth of mouse blastocysts cultured in vitro: evidence for the involvement of the cell recognition tripeptide Arg-Gly-Asp.

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Abstract
Differentiation of the nonadherent trophectoderm cells of the mammalian embryo into attachment competent trophoblast cells appears to be a prerequisite to invasion of the uterine stroma. To investigate the molecular basis of trophoblast differentiation free of maternal environmental constraints, we used a model system in which attachment and outgrowth of trophoblast cells occurs in vitro. Recently, it was found that either fibronectin or laminin, both of which are extracellular matrix glycoproteins of the uterine stroma, will support trophoblast outgrowth in vitro. In this study we report that the outgrowth of blastocysts on fibronectin-coated dishes is inhibited in a dose-dependent manner by the presence of a hexapeptide containing the sequence Arg-Gly-Asp, which has been shown previously to be recognized by the fibronectin receptor. This peptide had no effect on lamin-mediated trophoblast outgrowth, suggesting that the trophoblasts contain different cell surface receptors for fibronectin and laminin. Trophoblast attachment and limited outgrowth also could be obtained on dishes to which the hexapeptide Gly-Arg-Gly-Asp-Ser-Pro was coupled. Under these conditions, however, outward migration of the trophoblast cells appeared to be reduced. Vitronectin, another adhesion molecule that apparently binds to cells via a cell surface receptor that recognizes Arg-Gly-Asp sequences, also was capable of supporting trophoblast outgrowth. These findings suggest that differentiation of cells of the trophectoderm into trophoblast cells with an invasive phenotype may involve the production of cell surface receptors for fibronectin and possibly for other proteins that contain the Arg-Gly-Asp recognition sequence.