CHARACTERIZATION AND LOCALIZED EXPRESSION OF THE LAMININ-BINDING PROTEIN P40 (LBP/P40) GENE DURING SEA-URCHIN DEVELOPMENT/

We have isolated and characterized the expression of a cDNA clone from the sea urchin Strongylocentrotus purpuratus that encodes a protein v ery similar to LBP/p40, originally identified as a nonintegrin, 67-kDa laminin binding protein. The deduced amino acid sequence of the prote in, which we call spLBP/p40, shows significant similarity with the LEP /p40 from other sources, although significant divergence does occur at the carboxyl end. The S. purpuratus mRNA is present as a maternal tra nscript and its level remains constant until activation of zygotic tra nscription at the hatching blastula stage, whereupon the total spLBP/p 40 increases through the pluteus larval stage. Adult tissues also cont ain the spLBP/p40 mRNA. Both maternal and zygotic transcripts are tran slated as determined by their presence in polysomes. Immunoblot analys is using an antibody raised against a recombinant fusion protein indic ates that the concentration of the spLBP/p40 protein remains constant during development despite the postblastula increase in mRNA concentra tion. However, the spatial distribution of the protein changes from a uniform, intracellular distribution in all cells of cleavage and blast ula stages to localized, elevated levels in cells of the gut, primary mesenchyme, and oral epithelium of prism larvae. The distribution of s pLBP/p40 mRNA at different developmental stages, analyzed by in situ h ybridization, reflects that of the protein. Our results argue against a laminin binding function for this protein; instead they place the sp LBP/p40 gene in a class of previously described sea urchin genes invol ved in growth and proliferation. (C) 1995 Academic Press, Inc.