Sipunculan ParaHox genes

Our perspective on the origin and evolution of the Hox gene cluster changed with the discovery of the ParaHox gene cluster in amphioxus (Cephalochorda ta; Branchiostoma floridae) (Brooke et al. 1998). The ParaHox gene cluster contains three homeobox genes (Gsx, Xlox, Cdx) and is deduced to be a paral ogue (evolutionary sister) of the Hox gene cluster. If this deduction is co rrect, animals with Hox genes should also possess ParaHox genes. Paradoxica lly, however, only deuterostome animals have thus far been shown to contain all three ParaHox genes. Here we report the cloning of all three ParaHox g enes from each of two species within the phylum Sipuncula. This is the firs t demonstration of all three ParaHox genes in the genome of a protostome an imal and confirms that the common ancestor of protostomes and deuterostomes possessed all three ParaHox genes. Furthermore, it implies that the ParaHo x genes are of sufficient functional importance in both protostomes and deu terostomes that they have all been conserved in both of these bilaterian cl ades.