Embryonic expression of a hemichordate distal-less gene

Hemichordates occupy a critical phylogenetic position among deuterostomes b ecause they exhibit echinoderm-like larval morphology and chordate-like adu lt morphology. Analyses of the expression and function of hemichordate deve lopmental genes will therefore provide insight into the evolution of deuter ostome body plans. The distal-less/dlx gene encodes a homeodomain transcrip tion factor and plays roles in the development of appendages and the brain in a variety of animals. Here we have characterized a distal-less gene (Pf- dlx) of the hemichordate Ptychodera flava. During embryogenesis, Pf-dlx is expressed in the whole aboral ectoderm of the blastula and gastrula. Later, its expression appears in several cells in the boundary region between the oral and aboral ectoderm. The tornaria larvae express Pf-dlx in some speci fic cells of the ciliary band. The results are discussed in terms of an anc estral function of the distal-less/dlx gene in the formation of the nervous system.