Meeting Abstract
The Hox family of transcription factors have been well studied in many bilaterian clades and are generally thought to translate positional information along the primary body axis, the anterior-posterior axis, according to a “Hox code”. The Hox code includes aspects of spatial and temporal colinearity and functional dominance of more posterior Hox genes known as “posterior prevalence”. Here we use qPCR to show that Hox genes from a member of the sister group (Cnidaria) to the bilaterians, the starlet sea anemone, Nematostella vectensis, are activated earlier than previously reported and in a temporally colinear manner according to the presumed ancestral cnidarian Hox cluster. A bona fide anterior Hox gene (Ax6) is expressed at the animal (oral) pole and a bona fide posterior Hox gene (Ax1) in the vegetal (aboral) pole at blastula stage embryos. Using antisense morpholino knockdown and mRNA overexpression we show that, each gene not only patterns the differentiation of its own expression domain (e.g. anterior Hox expression is required for gastrulation/endomesoderm formation and oral development), but also impacts the development of the opposing pole, together patterning the entire oral-aboral axis. Furthermore, Ax6 and Ax1 interact with one another to control their respective oral and aboral expression domains. Interestingly we have noted that the posterior Hox gene negatively regulates oral development while the anterior Hox gene does not directly regulate aboral specification, thus showing signs of bilaterian “posterior prevalence”. These data support an ancient role for Hox genes to pattern the primary body axis of the cnidarian-bilaterian ancestor prior to gastrulation, demonstrate a rudimentary Hox code, and provide additional evidence that the oral pole of cnidarians is homologous to the anterior pole of bilaterians.
