A PROTEIN OF THE BASAL LAMINA OF THE SEA-URCHIN EMBRYO

The purification, biochemical characterization and functional features of a novel extracellular matrix protein are described. This protein i s a component oi the basal lamina found in embryos from the sea urchin species Paracentrotus lividus and Hemicentrotus puicherrimus. The pro tein has been named PI-200K or Hp-200K, respectively, because of the s pecies from which it was isolated and its apparent molecular weight in SDS-PAGE under reducing conditions. It has been purified from unferti lized eggs where it is found packed within cytoplasmic granules, and h as different binding affinities to type I collagen and heparin, as ass essed by affinity chromatography columns. By indirect immunofluorescen ce experiments it was shown that, upon fertilization, the protein beco mes extracellular, polarized at the basal surface of ectoderm cells, a nd on the surface of primary mesenchyme cells at the blastula and gast rula stages, The protein serves as an adhesive substrate, as shown by an in vitro binding assay where cells dissociated from blastula embryo s were settled on 200K protein-coated substrates. To examine the invol vement of the protein in morphogenesis of sea urchin embryo, early bla stula embryos were microinjected with anti-200K Fab fragments and furt her development was followed. When control embryos reached the pluteus stage, microinjected embryos showed severe abnormalities in arms and skeleton elongation and patterning. On the basis of current results, i t was proposed that 200K protein is involved in the regulation of sea urchin embryo skeletogenesis.