Characterization of a polymorphic protein localized to vascular epithelium in Botryllus schlosseri: role in tunic synthesis?

To develop an antibody-based screen for epitopes involved in botryllid historecognition, BALB/c mice were immunized with whole Botryllus schlosseri colonies. Resulting monoclonal antibodies were screened for alpha or beta fusibility types using enzyme-linked immunosorbent assay (ELISA) and immunohistochemical staining. One monoclonal antibody (109) that recognized a polymorphic epitope was further analyzed by Western blotting. It binds a species-specific epitope localized to the atrial siphon and blood vessels. The epitope does not cosegregate with fusibility type. A complementary DNA clone encoding this antigen contains an endoplasmic reticulum retention motif. Polymorphism observed on Western blots was confirmed by Northern blot analysis. This antigen provides a new polymorphic marker that may be useful in studies of tunic formation.