Identification of an intact ParaHox cluster with temporal colinearity but altered spatial colinearity in the hemichordate Ptychodera flava

Tetsuro Ikuta, Yi-Chih Chen, Rossella Annunziata, Hsiu-Chi Ting, Che-huang Tung, Ryo Koyanagi, Kunifumi Tagawa, Tom Humphreys, Asao Fujiyama, Hidetoshi Saiga, Nori Satoh, Jr-Kai Yu, Maria Ina Arnone, Yi-Hsien Su

ParaHox and Hox genes are thought to have evolved from a common ancestral ProtoHox cluster or from tandem duplication prior to the divergence of cnidarians and bilaterians. Similar to Hox clusters, chordate ParaHox genes including Gsx, Xlox, and Cdx, are clustered and their expression exhibits temporal and spatial colinearity. In non-chordate animals, however, studies on the genomic organization of ParaHox genes are limited to only a few animal taxa. Hemichordates, such as the Enteropneust acorn worms, have been used to gain insights into the origins of chordate characters. In this study, we investigated the genomic organization and expression of ParaHox genes in the indirect developing hemichordate acorn worm Ptychodera flava.