What's new in edition 48 part January 2007 Gene sites new with this edition

The Interactive Fly was first released July/August 1996, with updates provided at approximately one month intervals, through September 1997 (edition 13). Updating quarterly started with edition 14. With edition 40, the Interactive Fly began to schedule updates three times a year: fall, winter and spring.

Gene sites new with this edition of the Interactive Fly:

Centrosomin

A mitosis-specific Aurora-A kinase has been implicated in microtubule organization and spindle assembly in diverse organisms. However, exactly how Aurora-A controls the microtubule nucleation onto centrosomes is unknown. This study shows that Aurora-A specifically binds to the COOH-terminal domain of a Drosophila centrosomal protein, centrosomin (CNN), which has been shown to be important for assembly of mitotic spindles and spindle poles. Aurora-A and CNN are mutually dependent for localization at spindle poles, which is required for proper targeting of γ-tubulin and other centrosomal components to the centrosome. The NH₂-terminal half of CNN interacts with γ-tubulin, and induces cytoplasmic foci that can initiate microtubule nucleation in vivo and in vitro in both Drosophila and mammalian cells. These results suggest that Aurora-A regulates centrosome assembly by controlling the CNN's ability to targeting and/or anchoring γ-tubulin to the centrosome and organizing microtubule-nucleating sites via its interaction with the COOH-terminal sequence of CNN (Terada, 2003).

Dishevelled Associated Activator of Morphogenesis

Formins are involved in a wide range of cellular processes that require the remodeling of the actin cytoskeleton. This study analyzes a novel Drosophila formin, belonging to the recently described DAAM subfamily. In contrast to previous assumptions, it is shown that DAAM plays no essential role in planar cell polarity signaling, but it has striking requirements in organizing apical actin cables that define the taenidial fold pattern of the tracheal cuticle. These observations provide evidence the first time that the function of the taenidial organization is to prevent the collapse of the tracheal tubes. The results indicate that although DAAM is regulated by RhoA, it functions upstream or parallel to the non-receptor tyrosine kinases Src42A and Tec29 to organize the actin cytoskeleton and to determine the cuticle pattern of the Drosophila respiratory system (Matusek, 2006).

DNA replication-related element factor

The promoters of Drosophila genes encoding DNA replication-related proteins contain transcription regulatory element DRE (5'-TATCGATA) in addition to E2F recognition sites. A specific DRE-binding factor, DNA replication-related element factor or DREF, positively regulates DRE-containing genes. In addition, it has been reported that DREF can bind to a sequence in the hsp70 scs' chromatin boundary element that is also recognized by boundary element-associated factor, and thus DREF may participate in regulating insulator activity. To examine DREF function in vivo, transgenic flies were established in which ectopic expression of DREF was targeted to the eye imaginal discs. Adult flies expressing DREF exhibited a severe rough eye phenotype. Expression of DREF induces ectopic DNA synthesis in the cells behind the morphogenetic furrow that are normally postmitotic, and abolishes photoreceptor specifications of R1, R6, and R7. Furthermore, DREF expression caused apoptosis in the imaginal disc cells in the region where commitment to R1/R6 cells takes place, suggesting that failure of differentiation of R1/R6 photoreceptor cells might cause apoptosis. The DREF-induced rough eye phenotype is suppressed by a half-dose reduction of the E2F gene, one of the genes regulated by DREF, indicating that the DREF overexpression phenotype is useful to screen for modifiers of DREF activity. Among Polycomb/trithorax group genes, it was found that a half-dose reduction of some of the trithorax group genes involved in determining chromatin structure or chromatin remodeling (brahma, moira, and osa) significantly suppresses and that reduction of Distal-less enhances the DREF-induced rough eye phenotype. The results suggest a possibility that DREF activity might be regulated by protein complexes that play a role in modulating chromatin structure. Genetic crosses of transgenic flies expressing DREF to a collection of Drosophila deficiency stocks allowed identification of several genomic regions, deletions of which caused enhancement or suppression of the DREF-induced rough eye phenotype. These deletions should be useful to identify novel targets of DREF and its positive or negative regulators (Hirose, 2001).

Draper

Axon pruning is a common phenomenon in neural circuit development. Previous studies demonstrate that the engulfing action of glial cells is essential in this process. The underlying molecular mechanisms, however, remain unknown. draper (drpr), encoding an EGF-repeat single-pass transmembrane domain receptor, and ced-6, a phosphotyrosine-binding (PTB) domain protein each of which are essential for the clearance of apoptotic cells in C. elegans, function in the glial engulfment of larval axons during Drosophila metamorphosis. The drpr mutation and glia-specific knockdown of drpr and ced-6 by RNA interference suppress glial engulfment, resulting in the inhibition of axon pruning. drpr and ced-6 interact genetically in the glial action. Disruption of the microtubule cytoskeleton in the axons to be pruned occurs via ecdysone signaling, independent of glial engulfment. These findings suggest that glial cells engulf degenerating axons through drpr and ced-6. It is proposed that apoptotic cells and degenerating axons of living neurons are removed by a similar molecular mechanism (Awasaki, 2006).

Drosomycin

The initial description of the anti-fungal peptide Drosomycin is found in a study by Fehlbaum (1994). In response to a septic injury (pricking with a bacteria-soaked needle) larvae and adult Drosophila produce considerable amounts of a 44-residue peptide containing 8 cysteines engaged in intramolecular disulfide bridges. The peptide is synthesized in the fat body, a functional homologue of the mammalian liver, and secreted into the blood of the insect. It exhibits potent antifungal activity but is inactive against bacteria. This novel inducible peptide, Drosomycin, shows a significant homology with a family of 5-kDa cysteine-rich plant antifungal peptides isolated from seeds of Brassicaceae. This finding underlines that plants and insects can rely on similar molecules in their innate host defense (Fehlbaum, 1994).

Fps oncogene analog

Fes/Fer non-receptor tyrosine kinases regulate cell adhesion and cytoskeletal reorganisation through the modification of adherens junctions. Unregulated mammalian Fes/Fer kinase activity has been shown to lead to tumours in vivo. Drosophila Fer localises to adherens junctions in the dorsal epidermis and regulates a major morphological event, dorsal closure. Mutations in Src42A cause defects in dorsal closure similar to those seen in dfer mutant embryos. Furthermore, Src42A mutations enhance the dfer mutant phenotype, suggesting that Src42A and DFer act in the same cellular process. DFer is required for the formation of the actin cable in leading edge cells and for normal rates of dorsal closure. A gain-of-function mutation in dfer (dfer^gof) expresses an N-terminally fused form of the protein, similar to oncogenic forms of vertebrate Fer. dfer^gof blocks dorsal closure and causes axon misrouting. In dfer loss-of-function mutants ß-catenin (Armadillo) is hypophosphorylated, whereas in dfer^gof ß-catenin is hyperphosphorylated. Phosphorylated ß-catenin is removed from adherens junctions and degraded, thus implicating DFer in the regulation of adherens junctions (Murray, 2006),

Lazaro

During receptor-activated cell signaling cascades, it is important that the resynthesis of biochemical substrates is tightly coupled to their consumption by enzymatic reactions. This is particularly necessary in the context of neuronal signaling cascades, where at high rates of receptor stimulation, significant depletion of substrates might otherwise occur. An essential step in Drosophila phototransduction is the hydrolysis of phosphatidylinositol 4,5 bisphosphate (PI(4,5)P₂) by phospholipase Cβ (PLCβ) to generate a second messenger that opens the light-activated channels TRP and TRPL. Although the identity of this messenger remains unknown, recent evidence has implicated diacylglycerol kinase (DGK), encoded by rdgA, as a key enzyme that regulates levels of the second messenger, mediating both amplification and response termination within photoreceptor cells. This study demonstrates that lazaro (laza: from the Spanish novel Lazarillo de Tormes, in which Lazaro is the boy servant of a blind man and helps him to see) encodes a lipid phosphate phosphohydrolase (LPP) that functions during phototransduction. Whereas RdgA converts DAG to phosphatidic acid (PA) by adding phosphate residues to glycerol, Laza carries out the reverse reaction by removing the phosphate residue. In other words, DGK and LPP operate as a kinase/phosphatase pair that controls the level of PA. The activity of Laza laza rescues degeneration in the blind mutant rdgA and works synergistically with it to regulate amplification and response termination during phototransduction. Analysis of retinal phospholipids revealed a reduction in PA levels and an associated reduction in phosphatidylinositol (PI) levels. Together these results demonstrate the contribution of PI depletion to the rdgA phenotype and provide evidence that depletion of PI and its metabolites might be a key signal for TRP channel activation in vivo (Garcia-Murillas, 2006). Similar results have been obtained by (Kwon, 2006)

MTF-1

From insects to mammals, metallothionein genes are induced in response to heavy metal load by the transcription factor MTF-1, which binds to short DNA sequence motifs, termed metal response elements (MREs). A novel and seemingly paradoxical role is described for MTF-1 in Drosophila in that it also mediates transcriptional activation of Ctr1B, a copper importer, upon copper depletion. Activation depends on the same type of MRE motifs in the upstream region of the Ctr1B gene as are normally required for metal induction. Thus, a single transcription factor, MTF-1, plays a direct role in both copper detoxification and acquisition by inducing the expression of metallothioneins and of a copper importer, respectively (Selvaraj, 2005).

Mushroom body defect

During asymmetric cell division, the mitotic spindle must be properly oriented to ensure the asymmetric segregation of cell fate determinants into only one of the two daughter cells. In Drosophila neuroblasts, spindle orientation requires heterotrimeric G proteins and the Gα binding partner Pins, but how the Pins-Gαi complex interacts with the mitotic spindle is unclear. This study shows that Pins binds directly to the microtubule binding protein Mushroom body defect (Mud), the Drosophila homolog of Nuclear Mitotic Apparatus (NuMA) protein. Like NuMA, Mud can bind to microtubules and enhance microtubule polymerization. mud mutants form functional spindles and the neuroblasts are correctly polarized. Consistent with this, Brat and Numb form crescents in mud mutant neuroblasts, but the spindle is not aligned with them. Mitotic spindles in neuroblasts fail to align with the polarity axis. Therefore, the spindle orientation defect is a direct consequence of Mud loss of function. mud mutation can lead to symmetric segregation of the cell fate determinants Brat and Prospero, resulting in the misspecification of daughter cell fates and tumor-like overproliferation in the Drosophila nervous system. The data suggest a model in which asymmetrically localized Pins-Gαi complexes regulate spindle orientation by directly binding to Mud (Bowman, 2006; Izumi, 2006; Siller, 2006).

Nbs

Two protein kinases ATM and ATR as well as the Mre11/Rad50/Nbs (MRN) complex, which contains two highly conserved proteins Mre11 and Rad50 and a third less-conserved component, Nbs/Xrs2 (also known as nibrin), play critical roles in the response to DNA damage and telomere maintenance in mammalian systems. The primary function of the MRN complex is to sense DNA strand breaks and then to amplify the initial signal and convey it to downstream effectors, such as ATM, p53, Nbs1 (as a target of ATM), SMC1 and Brca1, that regulate cell cycle checkpoints and DNA repair. Mre11-Rad50 can bind DNA and that Mre11 possesses a nuclease activity that can process these ends. Nbs stimulates the DNA binding and nuclease activity by Mre11-Rad50. In vivo, Nbs is responsible for translocating the MRN complex to the nucleus and relocalizing the complex to the sites of DSBs following irradiation. The MRN complex is also required for activation of the S-phase checkpoint following DNA damage (Ciapponi, 2006).

Pcf11

The mechanism by which Pol II terminates transcription in metazoans is not understood. Pcf11 [mammalian homolog Pre-mRNA cleavage complex 2 protein Pcf11 (Pre-mRNA cleavage complex II protein Pcf11)] is directly involved in termination in Drosophila. Drosophila Pcf11 (referred to here is dPCF11) is concentrated at the 3' end of the hsp70 gene in cells, and depletion of dPcf11 with RNAi causes Pol II to readthrough the normal region of termination. dPcf11 also localizes to most transcribed loci on polytene chromosomes. Biochemical analysis reveals that dPcf11 dismantles elongation complexes by a CTD-dependent but nucleotide-independent mechanism and that dPcf11 forms a bridge between the CTD and RNA. This bridge appears to be crucial because an anti-CTD antibody, which also dismantles the elongation complex, is found to bridge the CTD to RNA. dPcf11 was observed to inhibit transcription at low, but not high, nucleotide levels, suggesting that dPcf11 dismantles paused elongation complexes. These results provide a biochemical basis for the dependency of termination on pausing and the CTD in metazoans (Zhang, 2006).

Ran

The Ran pathway has been shown to have a role in spindle assembly. However, the extent of the role of the Ran pathway in mitosis in vivo is unclear. Perturbation of the Ran pathway disrupts multiple steps of mitosis in syncytial Drosophila embryos and new mitotic processes have been uncovered that are regulated by Ran. During the onset of mitosis, the Ran pathway is required for the production, organization, and targeting of centrosomally nucleated microtubules to chromosomes. However, the role of Ran is not restricted to microtubule organization, because Ran is also required for the alignment of chromosomes at the metaphase plate. In addition, the Ran pathway is required for postmetaphase events, including chromosome segregation and the assembly of the microtubule midbody. The Ran pathway mediates these mitotic events, in part, by facilitating the correct targeting of the kinase Aurora A and the kinesins KLP61F and KLP3A to spindles (Silverman-Gavrila, 2006).

Resistance to Juvenile Hormone

The Methoprene-tolerant (Met) bHLH-PAS gene -- correctly termed Resistance to Juvenile Hormone (Rst(1)JH) -- is involved in juvenile hormone (JH) action in Drosophila as a likely component of a JH receptor. Met was expressed in Drosophila S2 cells, and MET partners were sought using pull-down assays. MET-MET interaction was found to occur. The germ-cell expressed (gce) gene is another Drosophila bHLH-PAS gene with high homology to Met; GCE forms heterodimers with MET. In the presence of JH or either of two JH agonists, MET-MET and MET-GCE formation is drastically reduced. Interaction between GCE and MET having N- or C-terminus truncations, bHLH or PAS-A domain deletions, or a point mutation in the PAS-B domain fail to occur. However, JH-dependent interaction occurs between GCE and MET having point mutations in bHLH or PAS-A. During development, changes in JH titer may alter partner binding by MET and result in different gene expression patterns (Godlewski, 2006).

Steamer duck

Integrins play a crucial role in cell motility, cell proliferation and cell survival. The evolutionarily conserved LIM protein PINCH is postulated to act as part of an integrin-dependent signaling complex. The molecular architecture of PINCH (Particularly Interesting New Cysteine-Histidine rich protein), which consists exclusively of multiple LIM domains (Hobert, 1999) suggests that it may function as a platform for the docking and/or productive juxtaposition of proteins involved in integrin signaling. In order to evaluate the role of PINCH in integrin-mediated cellular events, function of PINCH in Drosophila melanogaster was directly tested in vivo. The steamer duck (stck) alleles, that were first identified in a screen for potential integrin effectors (Prout, 1997), represent mutations in Drosophila pinch. stck mutants die during embryogenesis, revealing a key role for PINCH in development. Muscle cells within embryos that have compromised PINCH function display disturbed actin organization and cell-substratum adhesion. Mutation of stck also causes failure of integrin-dependent epithelial cell adhesion in the wing. Consistent with the idea that PINCH could contribute to integrin function, PINCH protein colocalizes with ßPS integrin at sites of actin filament anchorage in both muscle and wing epithelial cells. Furthermore, it is shown that integrins are required for proper localization of PINCH at the myotendinous junction. Integrin-linked kinase (Ilk), is also essential for integrin function. Drosophila PINCH and Ilk are complexed in vivo and are coincident at the integrin-rich muscle-attachment sites in embryonic muscle. Interestingly, Ilk localizes appropriately in stck mutant embryos, therefore the phenotypes exhibited by the stck mutants are not attributable to mislocalization of Ilk. These results provide direct genetic evidence that PINCH is essential for Drosophila development and is required for integrin-dependent cell adhesion (Clark, 2003).

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