Evolutionary history of the Brachyury gene in Hydrozoa: duplications, divergence and neofunctionalization.

Abstract

Brachyury, a member of T-box gene family, is widely known for its major role in mesoderm specification in bilaterians. It is also present in non-bilaterian metazoans, such as cnidarians, where it acts as a component of an axial patterning system. In this study, we present a phylogenetic analysis of Brachyury genes within phylum Cnidaria, investigate differential expression and address a functional framework of Brachyury paralogs in hydrozoan Dynamena pumila. Our analysis indicates two duplication events of Brachyury in the cnidarian lineage: in the common ancestor of the Medusozoa clade and at the base of the class Hydrozoa. We designate result of the first step as Brachyury2 and of the second as Brachyury3. Brachyury1 and 2 display a conservative expression pattern marking the oral pole of the body axis in D. pumila. On the contrary, Brachyury3 expression was detected in scattered presumably nerve cells of the D. pumila larva. Pharmacological modulations indicated that Brachyury3 is not under regulation of cWnt signalling in contrast to the other two Brachyury genes. Divergence in expression patterns and regulation suggest neofunctionalization of Brachyury3 in hydrozoans.