One of the biggest challenges currently facing the field of molecular oncology and developmental biology is to understand the complexity of signalling networks. One of the major coordinators in the signal networks is the Jun oncogene. Unraveling Jun's in vivo function will greatly advance our knowledge of signal transduction pathways in oncogenesis and development. We recently isolated the Drosophila jun (Djun) mutations and have shown that it relays JNK pathway to DPP (Drosophila TGF-b) pathway in regulating epithelial cell sheet movement for pattern formation of Drosophila embryo. The major goal of this research project is to dissect this Jun-mediated signal transduction pathway in Drosophila. Our major accomplishments this year are:1. We conducted a genetic screen for new components in this pathway and identified 15 new mutations. We mapped 10 of these mutations relative to known genetic markers by classical genetic techniques. These mutations have been carefully scrutinized genetically and phenotypically. Complementation tests have been done to assign these mutations to known genes, where possible. Detailed analysis of interesting mutations in both novel and previously identified loci are being pursued at molecular level.2. We have characterized one of the above mutations at molecular level. Mutation in this gene results in dpp overexpression in the leading edge cells, a phenotype that suggests that this gene may identify a negative regulator in the Jun pathway. The protein is predominantly localized in the nuclei. In tissue culture, this gene represses Jun's activity in activating gene transcription through AP-1 binding site. This gene may identify a JUN inhibitor, it was named Kjun (Killer of jun). Kjun encodes a 730 amino acid novel protein with several protein-protein interaction motifs.3. We plan to perform molecular genetic characterization of Kjun in both Drosophila and mouse. Work has begun to: (1) perform a comprehensive phenotypical analysis of Kjun in Drosophila, (2) identify KJUN domains that inhibit DJUN activity, (3) generate Kjun null mouse, (4) isolate KJUN interacting proteins, and (5) isolate genentic suppressors of a hypomorphic Kjun allele.
