Meeting Abstract
Hox genes are a set of transcription factors important for axial specification during development in bilaterally symmetrical animals (the Bilateria). The presence of Hox genes in the phylum Cnidaria, an outgroup of Bilateria, suggests that the origin of the Hox code and its function in axial patterning may predate Bilaterian evolution. To investigate the role of early Hox genes in axial patterning, we examined Hox gene expression during early development in the model sea anemone, Nematostella vectensis. Using quantitative PCR and in situ hybridization, we have determined that axially distinct Hox expression begins earlier in development than previously reported in cnidarians. At blastula stages, the anterior Hox gene Ax6 is expressed in the animal (oral) hemisphere and the maternally loaded posterior Hox gene Ax1 becomes spatially restricted to the vegetal (aboral) hemisphere. We functionally tested the role of Hox gene expression through mRNA overexpression and morpholino knockdown in early developing embryos. Overexpression and knockdown of the anterior Hox genes Ax6 and Ax6a resulted in hypertrophy or abnormal gastrulation and endomesoderm formation, respectively. Knockdown of Ax1 resulted in the absence of the apical tuft and metamorphosis. Our data also suggest the presence of reciprocal interactions between anterior and posterior Hox genes. We are currently investigating the role of signaling pathways that may be under Hox gene control, and generating stable transgenic animals to further identify the role of Hox genes in axial specification. These data demonstrate that Cnidarian Hox genes play an important role prior to gastrulation in the development of the oral-aboral axis and may provide insight into the earliest roles for Hox gene patterning in the bilaterian radiation.
