A HOMEOBOX GENE OF THE ORTHODENTICLE FAMILY IS INVOLVED IN ANTERO-POSTERIOR PATTERNING OF REGENERATING PLANARIANS

We studied the expression of DtOtx, a homeobox gene of the freshwater planarian Dugesia tigrina closely related to the Drosophila orthodenti cle (otd) and vertebrate Otx genes, which are known to control head de velopment in both fruit flies and vertebrates. DtOtx was not significa ntly expressed in adult planarians but it was activated within one hou r in regenerating tissues with a clearly asymmetric pattern. Animals s ectioned transversally, either between the head and the pharynx, or ca udal to the pharynx, give rise to a head-containing fragment regenerat ing a tail region and to a tail-containing fragment regenerating a hea d region. DtOtx was found to be activated in both regeneration blastem as but its transcripts were much more abundant in the head-regeneratin g tissues than in the tail-regenerating tissues. The same asymmetric d istribution of DtOtx transcripts was observed in central portions of t he body regenerating both head and tail structures and in animals late rally regenerating after a longitudinal cut. These data suggest a role of this gene in patterning the body axis of these primitive bilateria , at least during regeneration.