Homeotic transformation of thorax into head: Developmental analysis of a new Antennapedia allele in Drosophila melanogaster☆

Abstract A detailed analysis of the dominant and recessive mutant phenotypes of a recently discovered Antennapedia allele ( Antp PW ) was carried out. In heterozygous Antp PW flies a dominant homeotic transformation of the antenna into a second leg is observed. In addition, the vibrissae are transformed into a sternopleura, a structure which is also derived from the mesothoracic leg disc. Homozygotes survive until the late third larval instar and show a transformation of the mesothoracic segment into prothoracic and probably head structures. The anterior spiracles and the prothoracic (humeral) imaginal discs are degenerated. When homozygous Antp PW imaginal discs are transplanted into genetically marked wild-type hosts, the transformation of eye-antennal discs is identical to the dominant phenotype in heterozygous Antp PW flies, whereas all leg discs and the haltere disc develop into their normal structures. Surprisingly, the proximal compartment of the wing disc, which normally gives rise to the mesonotum, is transformed into head structures whereas the wing part of the disc is unaffected. These results provide further evidence that in the absence of the normal Antp + gene product putative head forming genes are expressed in the mesothorax. A strong correlation between the localization of Antp + transcripts as determined by in situ hybridization in the wild-type, and the sites of mutant defects caused by the recessive loss of Antp function is observed.