The sea urchin embryo possesses extracellular matrix layers lining the inside of the embryo (the basal lamina) and lining the outside of the embryo. The outer layer is divided into at least two layers, an apical lamina directly attached to the apical ends of the cells, and a slightly more exterior hyaline layer. In this micrograph, the basal lamina is immunostained with a monoclonal antibody (green) and the hyaline layer is immunostained with a second antibody (red).
The next several pages examine the role of the extracellular matrix during gastrulation