After this initial MS identification, we considered the crossreactivity of the crayfish proteins by western blot analysis using anti-hemocyanin antiserum raised against hemolymph hemocyanin of the shrimp Penaeus semisulcatus (Tom et al., 1993) (Fig.2A). The antibodies cross-reacted with both hemolymph and gastrolith hemocyanins from our crayfish but not with BSA, a negative control. We then employed the antibodies in an immunohistochemical assay
performed on sections of decalcified gastrolith pouches. Hematoxylin and eosin (H&E) staining (Fig.2B, left panel) shows the chitin layers forming the gastrolith matrix surrounded by the gastrolith-forming epithelium and its attached connective tissue. Green fluorescence indicates that the protein is present throughout the width of the chitinous structure but is especially concentrated along specific chitin layers (Fig.2B, middle image). Weak
immunostaining was also observed in the cytoplasm but not in the nuclei of the gastrolith-forming epithelium cells, while a stronger reaction was seen in the surrounding connective tissue (Fig.2B, middle and right panels).