NECTINS IN SEA-URCHIN EGGS AND EMBRYOS

The extracellular matrix of the sea urchin involves a protein with a m olecular 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 fibron ectin and sea urchin nectin have cell adhesion protein properties. The y are, however, different from each other in biochemical properties, b iological functions and intraembryonic distribution. Sea urchin fibron ectin isolated from the sea urchin ovary accelerates scattering of mic romere-derived cells and promotes spicule formation of micromeres in v itro. Sea urchin nectins identified so far in Paracentrotus lividus (L amarck), 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 const ituents, and to play some role in morphogenesis of the embryo.