Blackpatch, a neural degeneration mutation that interacts with the Notch locus in Drosophila

We have identified a gene in Drosophila melanogaster that is involved in the development of the adult eye and optic lobe of the brain and that interacts with facet alleles at the Notch locus. We have named this locus Blackpatch (Bpt). Mutant alleles of Bpt produce a variety of abnormal phenotypes in the presence of facet alleles. These phenotypes include neural degeneration in the eye and in the optic lobe of the adult brain that begins 60 hr after pupariation and produces a dark, necrotic eye spot in the adult eye. Other phenotypes include recessive embryonic lethality, pharate adult lethality, and premature adult death. We have isolated and characterized 10 Bpt alleles, all of which yield the neural eye/brain degeneration phenotype in individuals who are also homozygous or hemizygous for facet mutations. Only some of the facet alleles interact with Bpt. Bpt mutations also interact with the split mutation but do not interact with other types of Notch mutation. Somatic mosaic analysis and imaginal disc transplantation experiments suggest that the optic lobe of the brain may be the focus of Bpt action. We conclude that the Notch and Bpt genes have important functions during the interaction between the retina and the optic lobe of the brain.