Meeting Abstract
The gastrovascular cavity (GVC) is the primary site of digestion and nutrient absorption in cnidarians (hydroids, jellies, etc) and is lined by a layer of tissue derived from the embryonic endoderm. In most cnidarians, the GVC is populated by numerous enzymatic gland cells. Curiously, among anthozoans (corals, sea anemones, etc.), the GVC is lined by endoderm but the gland cells are restricted to the ectodermal layer of the pharynx and mesenteries. To better understand the relationship between cell identity and embryonic tissue identity, we characterized the development and cell biology of tissues associated with the GVC in the model sea anemone, Nematostella vectensis. Using light and electron microscopy, we describe the presence of several distinct gland cell types in the ectodermal portion of the pharynx and mesenteries in adult anemones. We further characterize the molecular identity of the mesenteries using RNA-Seq and show that the top-expressed genes from this tissue share homology with vertebrate digestive enzymes including chymotrypsins, phospholipase A2, and chitinase. Using in situ hybridization, we demonstrate the expression of several of these genes in ectodermal cells of the presumptive pharynx/mesenteries just after gastrulation, suggesting that enzyme-secreting cells are among the first internal cells to be specified in N. vectensis. While many of the upregulated genes from the mesenteries of N. vectensis are also specific to the gland cell lineage in Hydra, in the former these cells are derived from ectoderm and in the latter from endoderm. These data suggest that mis-expression of an endodermal cell lineage in an ectodermal tissue may have shaped the evolution of digestive system in cnidarians.
