ABSTRACT
Chitin is synthesized by a variety of organisms using enzymes called chitin synthases and was recently discovered in a number of aquatic vertebrates. In our ongoing investigations into the presence of vertebrate chitin, we unexpectedly found evidence of the polysaccharide within the electrosensory organs, known as Ampullae of Lorenzini, of diverse chondrichthyan fishes. Experiments with histochemical reagents, chemical analyses, and enzymatic digestions suggested that chitin is a component of the hydrogel filling the structures. Further, in situ hybridization with a sequence from the little skate (Leucoraja erinacea) revealed that chitin synthase expression is localized to cells inside the organs. Collectively, these findings suggest that chondrichthyan fishes endogenously synthesize chitin and beg further investigation into the function of chitin in the electrosensory system.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Subtle changes were made to the text and title. We clarified that the distribution of CBD signals were not on their own demonstrative of chitin. Further, we included new FTIR data (Fig. S2) from gel material subjected to our improved polysaccharide extraction protocol. We also added additional data to Fig. S2, namely SEM & AFM images of polysaccharides extracted from AoL gel as well as monosaccharide analysis of the gel before and after polysaccharides were extracted.
