Meeting Abstract
Hox genes have long been known to control embryonic formation of the anterior-posterior axis in bilaterians, and more recent work has shown them to be necessary for the formation of the oral-aboral axis during cnidarian embryogenesis. Here we investigate the role of Hox genes during asexual reproduction using the upside-down jellyfish, Cassiopea. Cassiopea is a scyphozoan that reproduces sexually at the medusa stage and asexually at the polyp stage. The clones produced asexually behave like larvae: both use cilia to swim with the future aboral pole facing forward. What genetic signals control the formation of these larva-like clones? Are Hox genes re-deployed in somatic tissue, or is this new individual’s body axis patterned by a different mechanism? To answer these questions, we present phylogenetic analyses of Hox genes from Hydrozoa, Scyphozoa, Staurozoa, and Cubozoa, as well as both both Hexacorallia and Octocorallia within Anthozoa. For the Cassiopea genes identified in this phylogeny, we characterize spatial and temporal expression by in situ hybridization. During embryogenesis, Cassiopea Hox genes are expressed in spatially restricted domains along the oral-aboral axis, consistent with a role in axial patterning and similar to patterns present in other cnidarians. Some Hox genes are also expressed during asexual reproduction in similar patterns, suggesting these genes serve a role after embryonic development to pattern the asexually produced individual. Characterizing the cnidarian Hox genes and understanding the full extent of their roles will provide insight into the Hox complement of the cnidarian-bilaterian ancestor and the origin of both cnidarian and bilaterian body forms.
