Meeting Abstract
Chitin is the second most abundant biopolymer on earth and is a major component of rigid biological structures such as the outer cuticle of arthropods (i.e. crabs and lobsters) and fungal cell walls. The molecule is produced by a myriad of organisms using a biosynthetic pathway involving enzymes called chitin synthases. Since the discovery of chitin, it had been widely assumed that vertebrates do not produce the polymer themselves. Recently, however, our lab discovered chitin synthase genes within a variety of vertebrates and identified chitin in many places from the gut lumen of zebrafish to the epidermis of both fishes and salamanders. In our ongoing investigations into vertebrate chitin, we unexpectedly discovered chitin within the electrosensory organs (known as ampullae of Lorenzini or AoL), of cartilaginous fish (chondrichthyans). All living organisms emit weak electric fields and chondrichthyans, such as sharks and rays, use their AoL to detect these fields in order to orient towards potential prey or mates. A single AoL consists of a tubular canal that on one side opens to the environment via a pore in the epidermis and terminates in a spherical structure made up of specialized electrosensory cells that are responsible for signal detection. We show that chitin is present within the viscous hydrogel which fills the whole tubular AoL of several evolutionarily distant Chondrichthyan species. In one species, we have identified the sequences of two chitin synthase genes and observed the localized expression of one of these genes to embryonic AoL. These data provide further evidence for the endogenous production of chitin by many types of vertebrates and characterize chitin’s presence in yet another distinct anatomical system. It remains to be studied how chitin contributes to the development and/or function of the chondrichthyan electrosensory system.
