IDENTIFICATION OF A CELL LINEAGE-SPECIFIC GENE CODING FOR A SEA-URCHIN ALPHA-2(IV)-LIKE COLLAGEN CHAIN

We report the isolation of several overlapping cDNAs from an embryonic library of Strongylocentrotus purpuratus coding for a novel sea urchi n collagen chain. The conceptual amino acid translation of the cDNAs i ndicated that the protein displays the structural features of a verteb rate type IV-like collagen a chain. In addition to a putative 31-resid ue signal peptide, the sea urchin molecule contains a 14-residue amino terminal non collagenous segment, a discontinuous 1,477 amino acid tr iple helical domain, and a 225-residue carboxyl-terminal domain rich i n cysteines. The amino- and carboxyl-terminal non collagenous regions of the echinoid molecule are remarkably similar to the 7 S and carboxy l-terminal non-collagenous (NC1) domains of the alpha 1 and alpha 2 ch ains of vertebrate type IV collagen. The sequence similarity and disti nct structural features of the 7 S and NC1 domains strongly suggest th at the sea urchin polypeptide is evolutionarily related to the alpha 2 (TV) class of collagen chains. Finally, in situ hybridizations reveale d that expression of this collagen gene is restricted to the mesenchym e cell lineage of the developing sea urchin embryo.