MOLECULAR-GENETICS OF ARISTALESS, A PRD-TYPE HOMEO BOX GENE INVOLVED IN THE MORPHOGENESIS OF PROXIMAL AND DISTAL PATTERN ELEMENTS IN A SUBSET OF APPENDAGES IN DROSOPHILA

Viable azistaless (al) mutations of Drosophila affect pattern elements at both ends of the proximodistal axis in a subset of adult appendages. The al gene has been cloned and identified by P-element-mediated germ-line transformation with a genomic DNA fragment, which rescues a lethal mutation of al as well as aspects of the adult al phenotype. The al gene contains a prd-type homeo domain and a Pro/Gln-rich domain and, hence, probably encodes a transcription factor. Its transcript distribution in third-instar imaginal discs closely corresponds to the anlagen of the tissues that later become visibly affected in adult al mutants. The striking similarity of a bimodal al expression in different imaginal discs indicates that al is under the control of a ''prepattern,'' which is shared at least among antennal, leg, and wing discs. The al gene is also transcribed during embryogenesis. Apart from a function in the ontogeny of specific larval head and tail organs, its embryonic transcript pattern suggests a possible role in early imaginal disc development.