THE HOMEOBOX GENE CUT INTERACTS GENETICALLY WITH THE HOMEOTIC GENES PROBOSCIPEDIA AND ANTENNAPEDIA

The cut locus (ct) codes for a homeodomain protein (Cut) and controls the identity of a subset of cells in the peripheral nervous system in Drosophila. During a screen to identify ct-interacting genes, we obser ved that flies containing a hypomorphic ct mutation and a heterozygous deletion of the Antennapedia complex exhibit a transformation of mout hparts into leg and antennal structures similar to that seen in homozy gous proboscipedia (pb) mutants. The same phenotype is produced with a ll heterozygous pb alleles tested and is fully penetrant in two differ ent ct mutant backgrounds. We show that this phenotype is accompanied by pronounced changes in the expression patterns of both ct and pi, in labial discs. Furthermore, a significant proportion of ct mutant flie s that are heterozygous for certain Antennapedia (Antp) alleles have t horacic defects that mimic loss-of-function Antp phenotypes, and ectop ic expression of Cut in antennal discs results in ectopic Antp express ion and a dominant Antp-like phenotype. Our results implicate ct in th e regulation of expression and/or function of two homeotic genes and d ocument a new role of ct in the control of segmental identity.