Embryonic cell invasiveness: an in vitro study of chick gastrulation

An investigation has been made into some of the possible mechanisms underlying the invasionary activity of gastrulating cells at the primitive streak of the early chick embryo. At gastrulation, epithelial cells in the upper epiblast layer of the embryo undergo a transformation into fibroblastic mesenchyme cells by passage through the primitive streak and penetration of a basement membrane. The resulting cells constitute the first embryonic mesoderm, which then invades the underlying tissue space. This phenomenon has been studied in vitro using the invasion of Matrigel, a reconstituted basement membrane, as a model. Mesoderm cells explanted into this matrix were subjected to treatments aimed at perturbing a number of putative mechanisms for cellular invasion. Application of inhibitors of glycosylation (tunicamycin) and oligosaccharide processing (castanospermine, deoxymannojirimycin, swainsonine) resulted in various degrees of inhibition of invasion. By contrast, cell binding fragments from fibronectin and laminin did not impede invasion, and neither did a panel of enzyme inhibitors, including serine protease and metalloprotease inhibitors. It is concluded that the primary determinant of the invasionary behaviour of these cells at gastrulation is a change in cell surface carbohydrate determinants, and that there is no evidence for the participation of localized enzymic activity. The medial disruption of the basement membrane seen at the primitive streak is therefore most likely to be due to local failure of synthesis, rather than local degradation.