GENETIC DISSECTION OF POINTED, A DROSOPHILA GENE ENCODING 2 ETS-RELATED PROTEINS

The Drosophila gene pointed (pnt) is required for the differentiation of a number of tissues during embryogenesis, including the ventral ect oderm, the nervous system, the tracheal system and certain muscle fibe rs. The phenotypes associated with strong pointed alleles are reflecte d by a complex pointed expression pattern during embryogenesis. Two pr omoters, PI and P2, separated by some 50 kb of genomic sequences, dire ct the transcription of two different transcript forms, encoding two d ifferent proteins related to the ETS family of transcription factors. To assess the individual functions of the two different pointed protei n forms, we have generated new pointed alleles affecting either the P1 or the P2 transcript, termed PI and P2 alleles, respectively. Genetic analysis reveals partial heteroallelic complementation between certai n pointed PI and P2 alleles. Surviving trans-heterozygous flies have r ough eyes, abnormal wings and halteres, suggesting a requirement for p ointed function during their imaginal disc development. Further geneti c analysis demonstrates that expression of a given pointed P2 allele d epends on trans-acting transcriptional regulatory sequences. We have i dentified two chromosomal domains with opposite regulatory effects on the transcriptional activity of the pointed P2 promoter, one trans-act ivates and the other trans-represses pointed P2 expression. By deletio n mapping we were able to localize these control regions within the 5' region of the pointed P2 transcript.