NECTINS IN SEA-URCHIN EGGS AND EMBRYOS

The extracellular matrix of the sea urchin involves a protein with a molecular weight of 180 kDa (sea urchin fibronectin), which corresponds to mammalian fibronectin, and a nectin specific to Echinoidea with a molecular weight of 105-115 kDa (sea urchin nectin). Sea urchin fibronectin and sea urchin nectin have cell adhesion protein properties. They are, however, different from each other in biochemical properties, biological functions and intraembryonic distribution. Sea urchin fibronectin isolated from the sea urchin ovary accelerates scattering of micromere-derived cells and promotes spicule formation of micromeres in vitro. Sea urchin nectins identified so far in Paracentrotus lividus (Lamarck), Temnopleurus hardwicki (Gray) and Pseudocentrotus depressus (A. Agassiz) are presumably homologous molecules displayed in different species. They seem to be secreted into the hyaline layer as its constituents, and to play some role in morphogenesis of the embryo.