The JAK/STAT signal transduction pathway controls numerous events in Drosophila melanogaster development. Receptors for the pathway have yet to be identified. Here we have identified a Drosophila gene that shows embryonic mutant phenotypes identical to those in the hopscotch (hop)/JAK kinase and marelle (mrl)/Stat92e mutations. We named this gene master of marelle (mom). Genetic analyses place mom's function between upd (the ligand) and hop. We further show that cultured cells transfected with the mom gene bind UPD and activate the HOP/STAT92E signal transduction pathway. mom encodes a protein distantly related to the mammalian cytokine receptor family. These data show that mom functions as a receptor of the Drosophila JAK/STAT signal transduction pathway.

Stem cells will undergo self-renewal to produce new stem cells if they are maintained in their niches. The regulatory mechanisms that recruit and maintain stem cells in their niches are not well understood. In Drosophila testes, a group of 12 nondividing somatic cells, called the hub, identifies the stem cell niche by producing the growth factor Unpaired (Upd). Here, we show that Rap-GEF/Rap signaling controls stem cell anchoring to the niche through regulating DE-cadherin-mediated cell adhesion. Loss of function of a Drosophila Rap-GEF (Gef26) results in loss of both germline and somatic stem cells. The Gef26 mutation specifically impairs adherens junctions at the hub-stem cell interface, which results in the stem cells "drifting away" from the niche and losing stem cell identity. Thus, the Rap signaling/E-cadherin pathway may represent one mechanism that regulates polarized niche formation and stem cell anchoring.

The Drosophila melanogaster JUN N-terminal kinase (DJNK) and DPP (decapentaplegic) signal transduction pathways coordinately regulate epithelial cell sheet movement during the process of dorsal closure in the embryo. By a genetic screen of mutations affecting dorsal closure in Drosophila, we have now identified a multidomain protein, connector of kinase to AP-1 (cka), that functions in the DJNK pathway and controls the localized expression of dpp in the leading-edge cells. We have also investigated how CKA acts. This unique molecule forms a complex with HEP (DJNKK), BSK (DJNK), DJUN, and DFOS. Complex formation activates BSK kinase, which in turn phosphorylates and activates DJUN and DFOS. These data suggest that CKA represents a novel molecule regulating AP-1 activity by organizing a molecular complex of kinases and transcription factors, thus coordinating the spatial-temporal expression of AP-1-regulated genes.Morphogenetic movements play a central role in the establishment of the overall body organization and shape during metazoan development. Most types of morphogenetic movements involve epithelial cell invagination and spreading (epiboly). In Drosophila melanogaster, the morphogenetic movement that occurs during dorsal closure (DC) of the embryonic epidermis has provided an excellent system for characterizing the molecular mechanisms underlying the coordinated movements of epithelial cell layers (8,13,25,26,38).DC is a major morphogenetic event that occurs during midembryogenesis. DC relies predominately on cell shape changes within the postmitotic epidermis. These changes are initiated in two symmetric dorsalmost rows of epidermal cells, known as the leading-edge (LE) cells, followed by the stretching of the more lateral epidermal cells, and are finished with the fusion of the two rows of LE cells at the dorsal midline (4,23,43).Embryos that fail to complete DC due to mutations in the genes required for this process die with a characteristic dorsalopen phenotype (14,27,29,41). Based on molecular data, two types of genes for DC have been identified. The first class identifies cytoskeletal and extracellular matrix components. These molecules may form the mechanical machinery that responds to signaling and drives cell shape changes. The second class identifies signaling molecules, including components in the D. melanogaster JUN N-terminal kinase (DJNK) signal transduction pathway and the dpp signal transduction pathway (8,13,25,26,38).Mutations in DJNK cascade genes block cell shape changes and disrupt organization of the cytoskeleton components at the LE. In addition, dpp gene expression is lost from the LE at the onset of DC. The Drosophila homologue of c -jun (Djun) is a central player in this signal transduction pathway (12,16,32). Djun mutations completely block epithelial cell sheet movement in DC. In doing so, DJUN is a target of the DJNK signal transduction pathway. DJNK may function by phosphorylating and activating DJUN, which in turn induces transcription of dpp in the LE cells during DC (12, 32). ...

In many tissues, two or more types of stem cells share a niche, and how the stem cells coordinate their self-renewal and differentiation is poorly understood. In the Drosophila testis, germ line stem cells (GSCs) and somatic cyst progenitor cells (CPCs) contact each other and share a niche (the hub). The hub expresses a growth factor Unpaired (Upd) that activates the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway in GSCs to regulate the stem cell self-renewal. Here, we demonstrate that the JAK/STAT signaling also regulates CPCs self-renewal. We also show that a negative regulator, the suppressor of cytokine signaling 36E (SOCS36E), suppresses JAK/ STAT signaling in somatic cells, preventing them from out-competing the GSCs. Furthermore, through selectively manipulating the JAK/STAT signaling level in either CPCs or GSCs, we demonstrate that the somatic JAK/STAT signaling is essential for self-renewal and maintenance of both CPCs and GSCs. These data suggest that a single JAK/STAT signal from the niche orchestrate the competitive and dependent co-existence of GSCs and CPCs in the Drosophila testis niche.

Birt-Hogg-Dube´syndrome (BHD) is a rare, inherited genodermatosis characterized by hair follicle hamartomas, kidney tumors and spontaneous pneumothorax. The BHD locus was mapped to chromosome 17p11.2 by linkage analysis, and germline mutations in a novel gene (BHD) were identified in a panel of BHD families. Using RNA interference to decrease expression of the Drosophila BHD homolog (DBHD), we have demonstrated that DBHD is required for male germline stem cell (GSC) maintenance in the fly testis. Reduction of DBHD gene activity suppresses the GSC overproliferation phenotype associated with overexpression of either unpaired (upd) or decapentaplegic (dpp). Further genetic interaction experiments suggest that DBHD regulates GSC maintenance downstream or in parallel of the JAK/ STAT and Dpp signal-transduction pathways. These findings suggest that the BHD protein may regulate tumorigenesis through modulating stem cells in human.

The JAK/STAT signal transduction pathway regulates many developmental processes in Drosophila. However, the functional mechanism of this pathway is poorly understood. In this report, we identify the Drosophila cyclin-dependent kinase 4 (Cdk4), which exhibits embryonic mutant phenotypes identical to those in the Hopscotch/JAK kinase and stat92E/STAT mutations. Specific genetic interactions between Cdk4 and hop mutations suggest that Cdk4 functions downstream of the HOP tyrosine kinase. We further show that Cyclin D-Cdk4 (as well as Cyclin E-Cdk2) binds and regulates STAT92E protein stability. STAT92E regulates gene expression for various biological processes, including the endocycle S phase. These data suggest that Cyclin D-Cdk4 and Cyclin E-Cdk2 play more versatile roles in Drosophila development.

Sperm storage in the female is a key factor for reproductive success in a variety of organisms, including Drosophila melanogaster. The spermathecae (SP) are the Drosophila organs for long-term storage. While wild-type female flies have two SP, occasionally, three or four SP have been observed in mutant flies. However, the molecular mechanism of SP formation is unknown. Here we show that loss of function of a Drosophila Rap-GEF (GEF26) result in an occurrence of the supernumerary SP; females have three SP (varies from 11 to 62% in different allele combinations) instead of the normal two SP. In addition, the Gef26 mutant flies also have ectopic wing veins and extra mechanosensory organs. The supernumerary SP phenotype of the Gef26 mutation can be enhanced by the Drosophila Rap mutations and rescued by overexpressing the cell adhesion molecule DE-cadherin. These data suggest that the Rap-GEF/Rap signaling controls the formation of supernumerary spermathecae through modulating cell adhesion in Drosophila.

With the completion of the nucleotide sequences of several complex eukaryotic genomes, tens of thousands of genes have been predicted. However, this information has to be correlated with the functions of those genes to enhance our understanding of biology and to improve human health care. The Drosophila transposon P-element-induced mutations are very useful for directly connecting gene products to their biological function. We designed an efficient transposon P-element-mediated gene disruption procedure and performed genetic screening for single P-element insertion mutations, enabling us to recover 2500 lethal mutations. Among these, 2355 are second chromosome mutations. Sequences flanking >2300 insertions that identify 850 different genes or ESTs (783 genes on the second chromosome and 67 genes on the third chromosome) have been determined. Among these, 455 correspond to genes for which no lethal mutation has yet been reported. The Drosophila genome is thought to contain ∼3600 vital genes; 1400 are localized on the second chromosome. Our mutation collection represents ∼56% of the second chromosome vital genes and ∼24% of the total vital Drosophila genes.