Multiple Hox/HOM-class homeoboxes in Platyhelminthes.

The importance of the Hox/HOM class of homeobox genes in early anterior-posterior pattern formation and the conserved genomic organization of this gene family provides an interesting study in genome evolution. The Platyhelminthes (flatworms) are a basal metazoan group with a simple bilateral body plan. We used the polymerase chain reaction (PCR) to detect Hox/HOM-class homeobox genes from species representing two classes of flatworms. Seven planarian and five trematode Hox/HOM-class homeoboxes were found. The sequences of the genes are consistent with the presence of one Hox/HOM-type cluster in the flatworms. Further analysis of this putative cluster may be expected to provide outgroup information for studying the evolution of the Hox/HOM clusters in the higher metazoa.