Chitin the Good Fight – Identification and Description of Chitin and Its Genes in Cnidaria

Abstract

This dissertation explores broad aspects of chitin biology in Cnidaria, with the aim of incorporating glycobiology with evolution and development. Chitin is the second-most abundant biological polymer on earth and is most commonly known in metazoans as a structural component of arthropod exoskeletons. This work seeks to determine whether chitin is more broadly distributed within early-diverging metazoans than previously believed, and whether it has novel non-structural applications in cnidarians. The Cnidaria (i.e., medusae, corals, sea anemones, cubomedusae, myxozoans) comprises over 11,000 described species exhibiting highly diverse morphologies, developmental programs, and ecological niches. Chapter 1 explores the distribution of chitin synthase (CHS) genes across Cnidaria. These genes are present in all classes and are expressed in life stages or taxa that do not have any reported chitinous structures. To further elucidate the biology of chitin in cnidarian soft tissues, in Chapters 2 and 3 I focus on the model sea anemone Nematostella vectensis, which has three chitin synthase genes – each with a unique suite of domains. Adult and developmental data show that the CHS genes are differentially expressed in Nematostella tissues, indicating that the chitin molecule has an integral role in the biology of this species. Disruption of genomic sequences for chitin synthase genes results in disorganized morphology in larvae and polyps, and a lack of spirocyst development. Histochemical labeling shows that chitin is distributed widely in endodermal and ectodermal tissues, and that it comprises the tubule of spirocysts. In the Appendix, I discuss a putative CHS gene cloned from the ctenophore species Pleurobrachia bachei. Chitin histochemical labeling localizes to a portion of the tentacle bulbs in both P. bachei and Mnemiopsis leidyi. Spacial gene expression of the putative Pb-CHS also localizes to the tentacle bulb. Understanding how early-diverging phyla like Cnidaria employ chitin may provide new insight into hitherto unknown functions of polysaccharides in animals as well as their role in the evolution of biological novelty.