Cloning and developmental expression of amphioxus Dachschund

The nuclear factor dachshund (dac) is a key regulator of eye and leg development in Drosophila. We have cloned a Dachshund homologue from an invertebrate chordate amphioxus (Branchiostoma floridae). Sequence comparison reveals a high degree of similarity of amphioxus Dachshund (AmphiDach) to the known vertebrate and Drosophila dachshund genes. AmphiDach is first expressed in the prospective paraxial mesoderm at the gastrula stage. At the early neurula stage, expression is detected in developing somites and anterior endoderm, but in late neurula transcripts are present exclusively in the most posterior region of the cerebral vesicle and the anterior pharynx endoderm. Then, in larva, AmphiDach is localized in photoreceptive neurons of the frontal eye, infundibular organ, and endostyle as well as in Hesse organs and in nerve cells scattered along the nerve cord. Comparison of Dach expression in amphioxus and vertebrates suggests that such patterns are relatively similar (because they are expressed in somites, photoreceptor cells and CNS), even if expression of AmphiDach in the endostyle has no counterparts in its vertebrate homolog, the thyroid.