Immunolocalization of Dpfp1, a byssal protein of the zebra mussel Dreissena polymorpha

The zebra mussel is one of only a few freshwater bivalves known to produce a byssus, This fibrous, proteinaceous and highly cross-linked structure all ows the mussel to attach to a variety of substrata and contributes to its n otoriety as a major freshwater biofouling species. We have successfully exp ressed a full-length version of Dreissena polymorpha foot protein 1 (Dpfp1) , a putative byssal thread precursor, and have used the recombinant protein as an antigen for polyclonal antibody production. Antisera obtained from r abbits immunized with recombinant Dpfp1 recognize the protein in western bl ots of extracts from foot tissue and byssal threads. On the basis of this e vidence, we conclude that Dpfp1 is a byssal precursor protein manufactured and stored in the foot of the mussel, Immunohistochemical localization of D pfp1 suggests that the protein is localized in secretory granules in a larg e gland surrounding the ventral groove of the foot. Only a subset of these glandular cells stockpiles the protein, implying that the zebra mussel foot is a complex organ capable of several distinct secretory activities involv ed in byssal thread formation. The uniform distribution of Dpfp1-containing cells suggests that the protein is a significant load-bearing component of zebra mussel byssal threads, although a more rigorous test of this hypothe sis awaits ultrastructural localization of the protein in mature byssal thr eads.