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Microsatellite polymorphisms in a wild population of Drosophila melanogaster.

Highly variable DNA polymorphisms called microsatellites are rapidly becoming the marker of choice in population genetic studies. Until now, microsatellites have not been utilized for Drosophila studies. We have identified eight polymorphic microsatellite loci in Drosophila melanogaster and used them to characterize the genetic variation in a wild population from the Tyrrell's winery in Australia. Microsatellites were isolated from a partial genomic DNA library. All microsatellites consist of (AC)n repeats ranging from n = 2 to n = 24. Six loci were assigned to chromosomal location by genetic mapping, with three loci on chromosome II, one locus on chromosome III and two loci on the X chromosome. Up to four microsatellite loci were multiplexed in the same reaction. Microsatellite variation is substantially greater than allozyme variation in the Tyrrell's Drosophila population. 80% of the microsatellite loci examined are polymorphic, compared with 28% of allozymes. The mean number of alleles per polymorphic locus is 5.2 in microsatellites compared with 3.0 in allozymes. The average observed heterozygosity of polymorphic microsatellites is 47% compared with 26% for allozymes. Microsatellite variation in Drosophila melanogaster is similar to that reported for other insects. Higher variability commends microsatellites over allozymes for genetic studies in Drosophila melanogaster.

Animals↗

Isolation and kinetic characterisation of myosin and myosin S1 from the Drosophila indirect flight muscles.

The potential to explore myosin function through the alternative exons and mutations of the single muscle myosin heavy chain gene, Mhc of Drosophila requires detailed kinetic analysis of the myosins. We have obtained microgram quantities of enzymatically active Drosophila myosin and subfragment 1 (S1) from dissected indirect flight muscles. Using recent developments in stopped-flow and flash-photolysis methods combined with fluorescent/light scattering technologies we have determined some of the key kinetic parameters of actin-myosin and myosin-nucleotide interactions. The rate of ATP-induced dissociation of actin from Drosophila myosin (0.23 microM(-1) s(-1)) and subfragment 1 (S1, 0.82 microM(-1) s(-1)) are both fast and similar to values measured for mammalian skeletal muscle myosins and S1 fragments respectively. The ATP-induced cross bridge dissociation of Drosophila acto.S1 is expected to be fast since, for a rapidly contracting muscle like the Drosophila flight muscle, the post power stroke cross bridge must detach rapidly from actin or become a drag on the contracting filament. ATP-induced detachment is preceded by ADP release and this is proposed as the rate-limiting step that defines muscle shortening velocity. We show that the affinity of ADP for acto.S1 at 400 microM is 2-3 fold weaker than fast vertebrate myosins. This leads to an estimate of the ADP release rate constant of 4000 s(-1). We show that this predicts a maximum shortening velocity very similar to that obtained from in vivo estimates of indirect flight muscle shortening. The data is therefore compatible with ADP dissociation limiting the in vivo shortening velocity.

Actins↗

Genetic and molecular analysis of synaptic vesicle recycling in Drosophila.

Following exocytosis, one of the major presynaptic events is replenishing synaptic vesicles (SVs) to ensure the possibility of continuous synaptic transmission. The nerve terminal is thought to recycle SVs through clathrin-mediated endocytosis and by a clathrin-independent pathway called "kiss and run". This review highlights the use of the genetic model organism, the fruit fly (Drosophila melanogaster), in dissecting the molecular mechanisms of clathrin-mediated endocytosis in recycling SVs at neuromuscular junctions (NMJs). Analyses of endocytotic mutants in Drosophila indicate that clathrin-mediated endocytosis may be essential for SV recycling, including a putative fast recycling mechanism uncovered recently. Further, a rather complex picture begins to emerge suggesting that clathrin-mediated endocytosis involves several sequential steps mediated by a large number of proteins. Finally, these studies also reveal that SV proteins may be selectively retrieved into nascent SVs by clathrin accessory proteins and defects in protein retrieval have significant impacts on synaptic transmission. Following the completion of the Drosophila Genome Project and the development of gene targeting and RNAi approaches, genetic studies in Drosophila have become increasingly efficient. Hence, Drosophila is expected to continue to serve as an important model organism for studies of SV recycling.

Animals↗

Regions of variant histone His2AvD required for Drosophila development.

One way in which a distinct chromosomal domain could be established to carry out a specialized function is by the localized incorporation of specific histone variants into nucleosomes. H2AZ, one such variant of the histone protein H2A, is required for the survival of Drosophila melanogaster, Tetrahymena thermophila and mice (R. Faast et al., in preparation). To search for the unique features of Drosophila H2AZ (His2AvD, also referred to as H2AvD) that are required for its essential function, we have performed amino-acid swap experiments in which residues unique to Drosophila His2AvD were replaced with equivalently positioned Drosophila H2A.1 residues. Mutated His2AvD genes encoding modified versions of this histone were transformed into Drosophila and tested for their ability to rescue null-mutant lethality. We show that the unique feature of His2AvD does not reside in its histone fold but in its carboxy-terminal domain. This C-terminal region maps to a short alpha-helix in H2A that is buried deep inside the nucleosome core.

Amino Acid Sequence↗

A human HOX4B regulatory element provides head-specific expression in Drosophila embryos.

Like other homeobox genes of the Antennapedia and bithorax complexes (collectively called the HOM complex), the Drosophila Deformed (Dfd) gene has structural homologues in the Hox/HOX complexes of mouse and humans, one of which is human HOX4B (refs 3, 4). Previous experiments indicated that HOX4B protein can specifically activate the expression of the endogenous Dfd transcription unit in Drosophila embryos and larvae. We therefore asked whether HOX4B cis-regulatory elements could mimic the function of a Dfd autoregulatory element in Drosophila embryos. Here we show that a HOX4B upstream element can surprisingly provide expression in a posterior head segment of Drosophila. One possible mechanism for the axial position-specificity of the human element may involve the conservation of a Dfd-specific autoregulatory circuit in both arthropod and chordate lineages. This possibility is supported by the finding that a Drosophila Dfd autoregulatory element supplies spatially localized expression in the hindbrain of mouse embryos.

Animals↗

Lithium- and valproate-induced alterations in circadian locomotor behavior in Drosophila.

Lithium and valproate are commonly used mood stabilizers, but their action pathways are not clearly understood. They also suffer from multiple toxic effects that limit their utility. Elucidating their action mechanisms could lead to newer agents and better understanding of the etiopathogenesis of bipolar disorder. We have expanded the study of signaling mechanisms of lithium and valproate by using Drosophila circadian locomotor activity as a robust behavioral assay that is amenable to genetic manipulations. We demonstrate that lithium affects the circadian system of Drosophila similarly to what has been reported in the mammalian studies. We show that lithium and valproate share effects on the circadian locomotor activity of Drosophila: they lengthen the period of circadian rhythms and increase arrhythmicity. Valproate exerts these effects in a weaker fashion than does lithium. We also tested the circadian alterations in multiple mutant lines of Drosophila bearing defects in the GSK-3beta gene and other clock genes in response to lithium administration. We show that lithium partially rescues the shortening of circadian period when the GSK-3beta gene is overexpressed only in specific circadian pacemaker neurons, thus implicating GSK-3beta as a component in lithium's effect on the circadian oscillator. Moreover, lithium also lengthens the period in GSK-3beta heterozygous mutants and doubletime long mutants. These results establish a basis for using Drosophila genetics to investigate more fully lithium and valproate action mechanisms.

Animals↗

A homologue of AMP-activated protein kinase in Drosophila melanogaster is sensitive to AMP and is activated by ATP depletion.

We have identified single genes encoding homologues of the alpha, beta and gamma subunits of mammalian AMP-activated protein kinase (AMPK) in the genome of Drosophila melanogaster. Kinase activity could be detected in extracts of a Drosophila cell line using the SAMS peptide, which is a relatively specific substrate for the AMPK/SNF1 kinases in mammals and yeast. Expression of double stranded (ds) RNAs targeted at any of the putative alpha, beta or gamma subunits ablated this activity, and abolished expression of the alpha subunit. The Drosophila kinase (DmAMPK) was activated by AMP in cell-free assays (albeit to a smaller extent than mammalian AMPK), and by stresses that deplete ATP (oligomycin and hypoxia), as well as by carbohydrate deprivation, in intact cells. Using a phosphospecific antibody, we showed that activation was associated with phosphorylation of a threonine residue (Thr-184) within the 'activation loop' of the alpha subunit. We also identified a homologue of acetyl-CoA carboxylase (DmACC) in Drosophila and, using a phosphospecific antibody, showed that the site corresponding to the regulatory AMPK site on the mammalian enzyme became phosphorylated in response to oligomycin or hypoxia. By immunofluorescence microscopy of oligomycin-treated Dmel2 cells using the phosphospecific antibody, the phosphorylated DmAMPK alpha subunit was mainly detected in the nucleus. Our results show that the AMPK system is highly conserved between insects and mammals. Drosophila cells now represent an attractive system to study this pathway, because of the small, well-defined genome and the ability to ablate expression of specific gene products using interfering dsRNAs.

AMP-Activated Protein Kinases↗

Structure and tissue-specific expression of the Drosophila melanogaster organellar-type Ca(2+)-ATPase gene.

A 14 kb genomic clone covering the organellar-type Ca(2+)-ATPase gene of Drosophila melanogaster has been isolated and characterized. The sequence of a 7132 bp region extending from 1.1 kb 5' upstream of the initiation ATG codon over the polyadenylation signal at the 3' end has been determined. The gene consists of nine exons including one with an exceptional size of 2172 bp representing 72% of the protein coding region. Introns are relatively small (< 100 bp) except for the 3' intron which has a size of 2239 bp, an exceptionally large size among Drosophila introns. Five of the introns are in the same positions in Drosophila, Artemia and rabbit SERCA1 Ca(2+)-ATPase genes. There is only one organellar-type Ca(2+)-ATPase gene in the Drosophila genome, as was shown by Southern-blot analysis [Váradi, Gilmore-Hebert and Benz (1989) FEBS Lett. 258, 203-207] and by chromosomal localization [Magyar and Váradi (1990) Biochem. Biophys. Res. Commun. 173, 872-877]. Primer extension and S1-nuclease assays revealed a potential transcription initiation site 876 bp upstream of the translation initiation ATG with a TATA-box 23 bp upstream of this site. Analysis of the 5' region of the Drosophila organellar-type Ca(2+)-ATPase gene suggests the presence of potential recognition sequences of various muscle-specific transcription factors and shows a region with remarkable similarity to that in the rabbit SERCA2 gene. The tissue distribution of expression of the organellar-type Ca(2+)-ATPase gene has been studied by in situ RNA-RNA hybridization on microscopic sections. A low mRNA abundance can be detected in each tissue of adult flies, suggesting a housekeeping function for the gene. On the other hand a pronounced tissue specificity of expression has also been found as the organellar-type Ca(2+)-ATPase is expressed at a very high level in cell bodies of the central nervous system and in various muscles.

Amino Acid Sequence↗

Identification and characterization of DAlk: a novel Drosophila melanogaster RTK which drives ERK activation in vivo.

BACKGROUND: The mammalian receptor protein tyrosine kinase (RTK), Anaplastic Lymphoma Kinase (ALK), was first described as the product of the t(2;5) chromosomal translocation found in non-Hodgkin's lymphoma. While the mechanism of ALK activation in non-Hodgkin's lymphoma has been examined, to date, no in vivo role for this orphan insulin receptor family RTK has been described. RESULTS: We describe here a novel Drosophila melanogaster RTK, DAlk, which we have mapped to band 53 on the right arm of the second chromosome. Full-length DAlk cDNA encodes a phosphoprotein of 200 kDa, which shares homology not only with mammalian ALK but also with the orphan RTK LTK. Analysis of both mammalian and Drosophila ALK reveals that the ALK family of RTKs contains a newly identified MAM domain within their extracellular domains. Like its mammalian counterpart, DAlk appears to be expressed in the developing CNS by in situ analysis. However, in addition to expression of DAlk in the Drosophila brain, careful analysis reveals an additional early role for DAlk in the developing visceral mesoderm where its expression is coincident with activated ERK. CONCLUSION: In this paper we describe a Drosophila melanogaster Alk RTK which is expressed in the developing embryonic mesoderm and CNS. Our data provide evidence for the existence of a DAlk RTK pathway in Drosophila. We show that ERK participates in this pathway, and that it is activated by DAlk in vivo. Expression patterns of dALK, together with activated ERK, suggest that DAlk fulfils the criteria of the missing RTK pathway, leading to ERK activation in the developing visceral mesoderm.

Amino Acid Sequence↗

Isolation and characterization of the cDNA and the gene for eukaryotic translation initiation factor 4G from Drosophila melanogaster.

Recent evidence supports the notion that the eukaryotic polypeptide chain initiation factor (eIF)4G plays a critical bridging role in coordinating other eIF involved in eukaryotic translation initiation. Here we report the isolation and characterization of a 5621-bp cDNA encoding Drosophila eIF4G. The longest ORF predicts a polypeptide of 1666 amino acids with a molecular mass of 183,940 Da and shares 25% amino acid identity with other eIF4G. The 5' untranslated region is 386 nucleotides long and contains seven AUG codons out of frame. The in vitro transcription/translation of the cDNA yielded a major polypeptide, which was specifically immunoprecipitated with an antibody against Drosophila eIF4G. This polypeptide has the same electrophoretic mobility as eIF4G purified from Drosophila melanogaster embryos. A conserved eIF4E-binding motif was found in Drosophila eIF4G. The gene maps at the 102E region of chromosome 4 and spans a genomic region of approximately 16 kb. It was found to contain 15 introns. A single RNA transcript of approximately 5.9 kb was detected by northern blotting of poly(A)-rich RNA prepared from Drosophila adults. The sequence upstream of the transcription initiation site lacks the consensus TATA box, but contains several sequences possibly involved in the regulation of transcription.

Amino Acid Sequence↗

DMAP-85: a tau-like protein from Drosophila melanogaster larvae.

Microtubule-associated proteins (MAPs) play major regulatory roles in the organization and integrity of the cytoskeletal network. Our main interest in this study was the identification and the analysis of structural and functional aspects of Drosophila melanogaster MAPs. A novel MAP with a relative molecular mass of 85 kDa from Drosophila larvae was found associated with taxol-polymerized microtubules. In addition, this protein bound to mammalian tubulin in an overlay assay and coassembled with purified bovine brain tubulin in microtubule sedimentation experiments. The estimated stoichiometry of 85-kDa protein versus tubulin in the polymers was 1:5.3 +/- 0.2 mol/mol. It was shown that the 85-kDa protein bound specifically to an affinity column of Sepharose-beta II-(422-434) tubulin peptide, which contains the sequence of the MAP binding domain on beta II-tubulin. Affinity-purified 85-kDa protein enhanced microtubule assembly in a concentration-dependent manner. This effect was significantly decreased by the presence of the beta II-(422-434) peptide in the assembly assays, thus confirming the specificity of the 85-kDa protein interaction with the C-terminal domain on tubulin. Furthermore, this protein also exhibited a strong affinity for calmodulin, based on affinity chromatographic assays. Monoclonal and polyclonal anti-tau antibodies, including sequence-specific probes that recognize repeated microtubule-binding motifs on tau, MAP-2, and MAP-4 and specific N-terminal sequences of tau, cross-reacted with the 85-kDa protein from Drosophila larvae. These results suggest that tau and Drosophila 85-kDa protein share common functional and structural epitopes. We have named this protein as DMAP-85 for Drosophila MAP.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

In developing Drosophila neurones the production of gamma-amino butyric acid is tightly regulated downstream of glutamate decarboxylase translation and can be influenced by calcium.

The presented work pioneers the embryonic Drosophila CNS for studies of the developmental regulation and function of gamma-amino butyric acid (GABA). We describe for the first time the developmental pattern of GABA in Drosophila and address underlying regulatory mechanisms. Surprisingly, and in contrast to vertebrates, detectable levels of GABA occur late during Drosophila neurogenesis, after essential neuronal proliferation and growth have taken place and synaptogenesis has been initiated. This timeline is almost unchanged when the GABA synthetase glutamate decarboxylase (GAD) is strongly misexpressed throughout the nervous system suggesting a tight post-translational regulation of GABA expression. We confirmed such GABA control mechanisms in an independent model system, i.e. primary Drosophila cell cultures raised in elevated [K+]. The data suggest that, in both systems, GABA suppression occurs via control of GAD activity. Using developing embryos and cell cultures as parallel assay systems for pharmacological and genetic studies we show that the negative regulation of GAD can be overridden by drugs known to elevate intracellular free [Ca2+]. Our results provide the basis for investigations of genetic mechanisms underlying the observed phenomenon, and we discuss the potential implications of this work for Drosophila neurogenesis but also for a general understanding of GAD regulation.

Animals↗

Drosophila host defense after oral infection by an entomopathogenic Pseudomonas species.

Drosophila has been shown to be a valuable model for the investigation of host-pathogen interactions. Study of the Drosophila immune response has been hampered, however, by the lack of true Drosophila pathogens. In nearly all studies reported, the bacteria used were directly injected within the body cavity of the insect, bypassing the initial steps of a natural interaction. Here, we report the identification of a previously uncharacterized bacterial species, Pseudomonas entomophila (Pe), which has the capacity to induce the systemic expression of antimicrobial peptide genes in Drosophila after ingestion. In contrast to previously identified bacteria, Pe is highly pathogenic to both Drosophila larvae and adults, and its persistence in larvae leads to a massive destruction of gut cells. Using this strain, we have analyzed the modulation of the larval transcriptome upon bacterial infection. We found that natural infection by Pe induces a dramatic change in larval gene expression. In addition to immunity genes, our study identifies many genes associated with Pe pathogenesis that have been previously unreported.

Animals↗

Ionizing radiation induces caspase-dependent but Chk2- and p53-independent cell death in Drosophila melanogaster.

Ionizing radiation (IR) can induce apoptosis via p53, which is the most commonly mutated gene in human cancers. Loss of p53, however, can render cancer cells refractory to therapeutic effects of IR. Alternate p53-independent pathways exist but are not as well understood as p53-dependent apoptosis. Studies of how IR induces p53-independent cell death could benefit from the existence of a genetically tractable model. In Drosophila melanogaster, IR induces apoptosis in the imaginal discs of larvae, typically assayed at 4-6 hr after exposure to a LD(50) dose. In mutants of Drosophila Chk2 or p53 homologs, apoptosis is severely diminished in these assays, leading to the widely held belief that IR-induced apoptosis depends on these genes in Drosophila. In this article, we show that IR-induced apoptosis still occurs in the imaginal discs of chk2 and p53 mutant larvae, albeit with a delay. We demonstrate that this phenomenon is a true apoptotic response because it requires caspase activity and the chromosomal locus that encodes the pro-apoptotic genes reaper, hid, and grim. We also show that Chk2- and p53-independent apoptosis is IR dose-dependent and is therefore probably triggered by a DNA damage signal. We conclude that Drosophila has Chk2- and p53-independent pathways to activate caspases and induce apoptosis in response to IR. This work establishes Drosophila as a model for p53-independent apoptosis, which is of potential therapeutic importance for inducing cell death in p53-deficient cancer cells.

Animals↗

Drosophila flies in "Evolution Canyon" as a model for incipient sympatric speciation.

The genetic basis of population divergence leading to adaptive radiation and speciation is a major unresolved problem of evolutionary biology. Molecular elucidation of "speciation genes" advanced recently, yet it remains without clear identification of the gene complexes participating in reproductive isolation between natural populations, particularly, in sympatry. Genetic divergence was discovered between Drosophila melanogaster populations inhabiting ecologically contrasting, opposite slopes in "Evolution Canyon" (EC), Mt. Carmel, Israel. Interslope migration of flies is easy and verified. Nevertheless, significant interslope D. melanogaster population divergence was established at EC involving habitat choice, mate choice, thermal and drought tolerances, adaptive genes, and mobile elements. Parallel patterns of stress tolerance, habitat choice, and mate choice were demonstrated in Drosophila simulans at EC, although on a smaller scale. However, some tests for interslope genetic differentiation in Drosophila, derived from the opposite EC slopes, gave somewhat controversial results. Here we present new empirical data on interslope genetic divergence of Drosophila at EC, and summarize previous supporting and controversial results. We suggest that Drosophila populations at EC represent a rare example, demonstrating how selection overrides migration, and propose an ad hoc ecological model of incipient sympatric divergence.

Adaptation, Biological↗

Use of double-stranded RNA interference in Drosophila cell lines to dissect signal transduction pathways.

We demonstrate the efficacy of double-stranded RNA-mediated interference (RNAi) of gene expression in generating "knock-out" phenotypes for specific proteins in several Drosophila cell lines. We prove the applicability of this technique for studying signaling cascades by dissecting the well-characterized insulin signal transduction pathway. Specifically, we demonstrate that inhibiting the expression of the DSOR1 (mitogen-activated protein kinase kinase, MAPKK) prevents the activation of the downstream ERK-A (MAPK). In contrast, blocking ERK-A expression results in increased activation of DSOR1. We also show that Drosophila AKT (DAKT) activation depends on the insulin receptor substrate, CHICO (IRS1-4). Finally, we demonstrate that blocking the expression of Drosophila PTEN results in the activation of DAKT. In all cases, the interference of the biochemical cascade by RNAi is consistent with the known steps in the pathway. We extend this powerful technique to study two proteins, DSH3PX1 and Drosophila ACK (DACK). DSH3PX1 is an SH3, phox homology domain-containing protein, and DACK is homologous to the mammalian activated Cdc42 tyrosine kinase, ACK. Using RNAi, we demonstrate that DACK is upstream of DSH3PX1 phosphorylation, making DSH3PX1 an identified downstream target/substrate of ACK-like tyrosine kinases. These experiments highlight the usefulness of RNAi in dissecting complex biochemical signaling cascades and provide a highly effective method for determining the function of the identified genes arising from the Drosophila genome sequencing project.

Animals↗

gamma-Tubulin function during female germ-cell development and oogenesis in Drosophila.

A series of unconventional microtubule organizing centers play a fundamental role during egg chamber development in Drosophila. To gain a better understanding of their molecular nature, we have studied the centrosomal component gamma-tubulin during Drosophila oogenesis. We find that although single mutations in either of the two gamma-tubulin genes identified in Drosophila do not affect oogenesis progression the simultaneous depletion of both protein products has severe consequences. The combination of loss-of-function mutant alleles for the two gamma-tubulin genes leads to mitotic defects in female germ cells, resulting in agametic ovaries. A combination of weaker mutant alleles instead allows female germ-cell development to proceed, although the resulting egg chambers display pleiotropic abnormalities, most frequently affecting the number of nurse cells and oocytes per egg chamber. Thus, gamma-tubulin is required for several processes at different stages of germ-cell development and oogenesis, including oocyte determination and differentiation. Our data provide a functional link between a component of the peri-centriolar material, such as gamma-tubulin, and microtubule organization during Drosophila oogenesis. In addition, our results show that gamma-tubulin is required for female germ-cell proliferation and that the two gamma-tubulins present in Drosophila are functionally equivalent during female germ-cell development and oogenesis.

Animals↗

Drosophila DEG/ENaC pickpocket genes are expressed in the tracheal system, where they may be involved in liquid clearance.

The Drosophila tracheal system and mammalian airways are branching networks of tubular epithelia that deliver oxygen to the organism. In mammals, the epithelial Na(+) channel (ENaC) helps clear liquid from airways at the time of birth and removes liquid from the airspaces in adults. We tested the hypothesis that related Drosophila degenerin (DEG)/ENaC family members might play a similar role in the fly. Among 16 Drosophila DEG/ENaC genes, called pickpocket (PPK) genes, we found 9 expressed in the tracheal system. By in situ hybridization, expression appeared in late-stage embryos after tracheal tube formation, with individual PPK genes showing distinct temporal and spatial expression patterns as development progressed. Promoters for several PPK genes drove reporter gene expression in the larval and adult tracheal systems. Adding the DEG/ENaC channel blocker amiloride to the medium inhibited liquid clearance from the trachea of first instar larvae. Moreover, when RNA interference was used to silence PPK4 and PPK11, larvae failed to clear tracheal liquid. These data suggest substantial molecular diversity of DEG/ENaC channel expression in the Drosophila tracheal system where the PPK proteins likely play a role in Na(+) absorption. Extensive similarities between Drosophila and mammalian airways offer opportunities for genetic studies that may decipher further the structure and function of DEG/ENaC proteins and development of the airways.

Amiloride↗