cDNA for R-cognin: homology with a multifunctional protein

Retina cognin (R-cognin) is a developmentally regulated 50-kDa protein that was isolated from chicken embryo retina cell membranes. It mediates the adhesion and reaggregation in vitro of retina cells from chicken and mouse embryos, but not of cells from other tissues, and may be involved in neuronal differentiation. We report here the cloning of a cDNA for R-cognin. A chicken embryo retina cDNA library was constructed in lambda gt11 vector and was screened with polyclonal R-cognin antiserum, yielding several immunoreactive clones. Antiserum prepared to the R-cognin-beta-galactosidase fusion protein produced by one recombinant lysogen recognized the 50-kDa R-cognin protein derived from retina cell membranes. This antiserum inhibited the reaggregation of dissociated retina cells and immunostained chicken embryo retina tissue in a pattern similar to that obtained with R-cognin antiserum. In vitro translation of RNA from a cDNA subclone yielded a 50-kDa protein that was recognized by R-cognin antiserum on a Western blot. By these criteria we identify the cDNA clone as representative of the gene encoding R-cognin. This cDNA is nearly identical to a major portion of the cDNA for the multifunctional protein that is the beta subunit of prolyl 4-hydroxylase and has both protein disulfide isomerase activity and thyroid hormone-binding activity. These findings demonstrate that R-cognin differs from other cell adhesion molecules and suggest possible mechanisms for its action in cell adhesion and neuronal differentiation.