Serological and partial molecular characterization of a Thy-1 homolog in tunicates.

The occurrence of a Thy-1 homolog in the tissues of the advanced invertebrate group of tunicates has been investigated by using two monoclonal antibodies specific to rodent Thy-1.1 determinants and a heterologous anti-rat Thy-1 antiserum. In cellular and soluble-phase radioimmunoassays for Thy-1 using intact hemocytes, tissue extracts and hemolymph, membrane-bound and soluble Thy-1.1 cross-reacting determinants have been detected. Immunoprecipitation experiments with hemocyte deoxycholate extracts and hemolymph, labeled with 125I by lactoperoxidase/chloramine T and with NaB3H4 by galactose oxidase, established the association of the Thy-1.1 cross-reacting determinants with a single glycoprotein of apparent m.w. estimated at 27 000 in hemocytes and 22 500 in hemolymph by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The significance of this finding is discussed in relation to the phylogenetic emergence of the Thy-1 molecule during evolution.