Comparative analysis of Brachyury T-domains, with the characterization of two new sponge sequences, from a hexactinellid and a calcisponge

The Brachyury family of T-domain containing transcription factor has been recently the subject of a number of Evo-Devo studies, with expression data obtained from a wide sampling of eumetazans, pointing to a possible conserved role in the formation of the blastopore and the extremities of the digestive tract. Here we present a comparative analysis of Brachyury sequences at the metazoan scale, using published data and two new sponge Brachyury sequences. Alignment features, gene phylogeny, and the evolution of variable positions within the T-domain are discussed in the light of available data about functional constraints on the residues. Interestingly, the high sequence divergence observed in Brachyury T-domains from sponges appears to be mostly the consequence of autapomorphic changes within the sponge lineages, rather than the retention of primitive character states.