Powerful genetic tools, in combination with excellent cytological markers, make the Drosophila system an excellent model to address cell biology and whole-animal problems. We are studying cell signaling in male germline stem cells (GSCs) and animal aging in the Drosophila system. Cancers are age-related diseases and may originate from a few transformed cancer stem cells. The knowledge gained from the Drosophila system will form the scientific foundation for the study of aging, cancer stem cells, and regenerative medicine.The following is a brief description of our approaches and current projects: I. Developing the Drosophila models of the JAK/STAT and JNK/JUN signal transduction pathwaysI identified the Drosophila stat and jun genes' mutations during my postdoctoral fellow research at Harvard Medical School. During my first few years at the National Cancer Institute, my group concentrated on identifying components of the JAK/STAT and JNK/JUN signal transduction pathways to understand the signal transduction mechanism. We first conducted a large-scale, transposon P-element-mediated gene disruption screen. We screened 50,000 single P-element insertion mutations, which enabled us to recover 2500 lethal mutants. Sequences flanking 2300 lethal insertions were determined that identify 900 different genes or ESTs (Oh et al., Genetics, 163:195-201, 2003). We then conducted a secondary germline clonal screen using the library of P-element mutations to identify genes that function in the JAK/STAT and JNK/JUN signal transduction pathways. From that screen, we identified a receptor for the JAK/STAT signal transduction pathway (Chen et al., Genes Dev. 16:388-398, 2002); we also found that Cyclin D/Cdk4 functions in the JAK/STAT signal transduction pathway (Chen et al., Dev Cell 4:179-190, 2003). We further demonstrated that the JAK/STAT pathway and Cyclin D/Cdk4 cooperatively regulate tumor development in the fly blood and eye. In the JNK/JUN signal transduction pathway, we cloned a new gene [connector of kinase to AP-1 (cka)], which encodes a multidoman scaffolding protein of the JNK/JUN signal transduction pathway (Chen et al., Mol. Cell. Biol. 22:1792-1803, 2002). II. Signalings that regulate male GSC self-renewal or differentiationThe JAK/STAT and its interacting signal transduction pathways regulate male GSC self-renewal in Drosophila; the JNK/JUN and its interacting signal transduction pathways regulate stress response and lifespan in the fly. We are currently studying the molecular mechanisms of stem-cell self-renewal and animal aging in Drosophila. The following sections briefly describe our recent accomplishments and continuing works.1. A novel small GTPase guanine nucleotide exchange factor controls stem-cell maintenance through regulating adherens junction positioning and cell adhesion in the Drosophila testis.In a genetic screen for mutations that interact with the JAK/STAT signal transduction pathway in regulating male GSC fates, we identified a novel small GTPase guanine nucleotide exchange factor (NGEF) from our library of P-element mutations. Mutations of NGEF cause loss of both GSCs and somatic stem cells (SSCs) in the fly testis. We demonstrated that the NGEF controls recruitment of stem-cells to the niche by regulating DE-cadherin-mediated cell adhesion. NGEF is enriched at the interface between the hub and stem cells. The NGEF mutation specifically impairs adherens junctions at the hub-stem cell interface, which causes the stem cells to """"""""walk away"""""""" from the niche and lose stem-cell identity. 2. Work is continuing on NGEF.There is one human (hNGEF) and one mouse (mNGEF) homologues of the fly NGEF. a.One fellow is working on knocking out the mNGEF gene. b.The hNGEF was mapped to 4q32.1. Several human disease candidate genes have been mapped to this location
