Pl-nectin, a discoidin family member, is a ligand for beta C integrins in the sea urchin embryo.

Pl-nectin is a component of the extracellular matrix that surrounds embryos of the sea urchin Paracentrotus lividus. Pl-nectin mediates adhesion of dissociated embryonic cells to substrates and interfering with ectodermic cells contacting Pl-nectin results in defects in skeleton growth and morphogenesis. Recently, we reported that Pl-nectin is a new member of the discoidin family, in agreement with the notion that many discoidin-containing proteins are involved in cell adhesion processes as integrin ligands. To better understand the molecular basis for the interaction of Pl-nectin with ectoderm, we investigated the hypothesis that Pl-nectin is an integrin ligand in sea urchin embryos. We show that in P. lividus embryos, beta C-containing integrins localize to the apical surface of ectodermic cells, which are in contact with Pl-nectin. Immunoprecipitation experiments indicate that the two proteins are part of a complex in vivo and affinity chromatography indicates that beta C-containing integrin receptors bind purified PI-nectin. These data support a model in which ectodermic integrins binding to Pl-nectin mediate cellular adhesion to the hyaline layer. Regulated adhesion of cells to the hyaline layer is a critical component of several morphogenetic processes and the identification of the receptors and ligands involved provides new opportunities to investigate the underlying molecular mechanisms of ECM adhesion and morphogenesis. (C) 2010 Elsevier B.V. All rights reserved