Expression of dachshund in wild-type and Distal-less mutant Tribolium corroborates serial homologies in insect appendages

We isolated the homologue of the Drosophila gene dachshund (dac) from the b eetle Tribolium castaneum. Tc'dac is expressed in all appendages except uro gomphi and pleuropodia. Tc'dac is also active in the head lobes, in the ven tral nervous system, in the primordia of the Malpighian tubules and in bila teral stripes corresponding to the presumptive dorsal midline. Expression o f Tc'dac in the labrum lends support to the interpretation that the insect labrum is derived from a metameric appendage. The legs of Tribolium accommo date two Tc'dac domains, of which the more distal one corresponds to the si ngle dac domain described for Drosophila leg discs. In contrast to Drosophi la, where this domain is thought to intercalate between the homothorax (hth ) and the Distal-less (Dll) domains, in Tribolium it arises from within the Dll domain. In embryos mutant for the TC'Dll gene we find that the distal Tc'dac domain in the legs, as well as the expression in the labrum, are del eted while the proximal leg domain and the mandibular expression are unaffe cted. Based on Tc'dac expression in wild-type and mutant embryos, we demons trate serial homology of the complete mandible with the coxa of the thoraci c legs, which affirms the gnathobasic nature of the insect mandible.