Distribution of fibronectin in the ectoderm of gastrulating chick embryos

Abstract

A GLYCOPROTEIN known as large external transformation-sensitive (LETS) protein, cell surface protein (CSP) or fibronectin^1–3 can be identified on the surface of various cell types¹. This protein has a molecular weight of 210,000–250,000 and is closely related to the cold-insoluble globulin found in serum and to the factor needed for cell spreading in vitro^4,5. In culture many cells secrete fibronectin into the growth medium and on to the substratum^6–8; fibroblasts and other cells of mesodermal origin produce particularly large amounts. However, in the early mammalian embryo fibronectin is present in basement membranes before the mesoderm has formed, when the embryo consists only of ectoderm and endoderm⁹. Adult epithelia also produce fibronectin in vitro¹⁰, and it forms a component of epithelial basement membranes in vivo^11–13. We have applied an immunofluorescent technique to whole mounts of early chick embryos to examine the distribution and possible morphogenetic function of fibronectin. We discuss our results here, and suggest that fibronectin is involved in morphogenetic movement during early development.