Developmental studies of lethality associated with the antennapedia gene complex in Drosophila melanogaster

A number of dominant homoeotic mutations are localized to the proximal right arm of chromosome 3 of Drosophila melanogaster and are thought to represent members of a gene complex that controls normal determinative decisions in the head and thorax. We have designated this complex the Antennapedia gene complex (ANT-C). Developmental studies were done to investigate the nature of the lethality associated with members of two of the complementation groups within ANT-C. The first complementation group, represented by the mutant Multiple Sex Combs (Msc) is characterized by embryonic lethality when heterozygous with a deletion of the ANT-C. The second complementation group consists of Antennapedia (Antp), Antennapedia-Extra Sex Combs (Antp^Scx), and the lethals recovered as revertants of Antp^Ns. When heterozygous for a deletion of the ANT-C or in heterozygous condition with each other, the members of this group show effective lethal phases spanning from embryo-larval boundary to late larval stages. Wakimoto and Kaufman (1981) show that the Antp⁺ gene acts to establish normal determinative states in the thorax. In the present work, transplantation of eye-antennal disks from lethal individuals heterozygous for two different Antp^Ns revertant chromosomes into wild-type hosts allowed the assessment of the function of the Antp⁺ allele in the antenna. Since these transplants formed only antennal structures and showed no evidence of the antennal → leg transformation seen in Antp^Ns controls, we conclude that the wild-type function of the Antp locus is not necessary for the establishment and/or maintenance of the antennal determined state. We suggest that regulatory mechanisms associated with the Antp⁺ structural gene normally function both to allow its expression in the thorax and to repress it in the antenna.