Immunolocalization of hyalin in sea urchin eggs and embryos using an antihyalin-specific monoclonal antibody

Monoclonal antibodies were raised against purified cortical secretory vesicles (CVs) from the eggs of Strongylocentrotus purpuratus. One of the monoclonal antibodies (MAb 69-10, an IgA) was shown by immunofluorescence labeling of intact and detergent-lysed CVs to be directed against a CV content antigen. Immunoblot analysis of CVs revealed that MAb 69-10 bound to a major CV polypeptide with an Mr similar to that of hyalin (i.e., 300,000). MAb 69-10 was subsequently shown to bind to purified hyalin prepared from S. purpuratus and to cross react with hyalin prepared from Lytechinus pictus. Immunogold labeling on thin sections of unfertilized S. purpuratus eggs showed that hyalin was localized to the electron-lucent portion of CVs. This result is in agreement with the labeling pattern obtained by Hylander and Summers (Dev Biol 93:368-380, 1982) using polyclonal antihyalin antibodies. In fertilized eggs and later-stage embryos, hyalin was observed to be located on the external surface of the embryo. MAb 69-10 should be useful in studies of the structure of hyalin and its function in morphogenesis.