Fibronectin and laminin in the extracellular matrix and basement membrane of sea urchin embryos.

Fibronectin and laminin have been found in the extracellular matrix and in the basement membrane of sea urchin embryos during early development. These glycoproteins are also found on the cell surfaces of the outer epithelial layer and on the secondary mesenchyme cells within the blastocoel. The similarity of functions of the extracellular matrix and basement membrane is discussed, as is the similarity of their molecular components. These observations suggest the possibility that fibronectin and laminin form a continuous matrix surrounding the cells which links the outer ECM (hyaline layer) to the inner ECM (basement membrane). Such a network could coordinate the various activities of the embryo during early morphogenesis.