An inverse PCR screen for the detection of P element insertions in cloned genomic intervals in Drosophila melanogaster

A critical component of meiotic drive in Neurospora is located near a chromosome rearrangement

Neurospora fungi harbor a group of meiotic drive elements known as Spore killers (Sk). Spore killer-2 (Sk-2) and Spore killer-3 (Sk-3) are two Sk elements that map to a region of suppressed recombination. Although this recombination block is limited to crosses between Sk and Sk-sensitive (Sk(S)) strains, its existence has hindered Sk characterization. Here we report the circumvention of this obstacle by combining a classical genetic screen with next-generation sequencing technology and three-point crossing assays. This approach has allowed us to identify a novel locus called rfk-1, mutation of which disrupts spore killing by Sk-2. We have mapped rfk-1 to a 45-kb region near the right border of the Sk-2 element, a location that also harbors an 11-kb insertion (Sk-2(INS1)) and part of a >220-kb inversion (Sk-2(INV1)). These are the first two chromosome rearrangements to be formally identified in a Neurospora Sk element, providing evidence that they are at least partially responsible for Sk-based recombination suppression. Additionally, the proximity of these chromosome rearrangements to rfk-1 (a critical component of the spore-killing mechanism) suggests that they have played a key role in the evolution of meiotic drive in Neurospora.

The arouser EPS8L3 gene is critical for normal memory in Drosophila

The genetic mechanisms that influence memory formation and sensitivity to the effects of ethanol on behavior in Drosophila have some common elements. So far, these have centered on the cAMP/PKA signaling pathway, synapsin and fas2-dependent processes, pumilio-dependent regulators of translation, and a few other genes. However, there are several genes that are important for one or the other behaviors, suggesting that there is an incomplete overlap in the mechanisms that support memory and ethanol sensitive behaviors. The basis for this overlap is far from understood. We therefore examined memory in arouser (aru) mutant flies, which have recently been identified as having ethanol sensitivity deficits. The aru mutant flies showed memory deficits in both short-term place memory and olfactory memory tests. Flies with a revertant aru allele had wild-type levels of memory performance, arguing that the aru gene, encoding an EPS8L3 product, has a role in Drosophila memory formation. Furthermore, and interestingly, flies with the aru^8–128 insertion allele had deficits in only one of two genetic backgrounds in place and olfactory memory tests. Flies with an aru imprecise excision allele had deficits in tests of olfactory memory. Quantitative measurements of aru EPS8L3 mRNA expression levels correlate decreased expression with deficits in olfactory memory while over expression is correlated with place memory deficits. Thus, mutations of the aru EPS8L3 gene interact with the alleles of a particular genetic background to regulate arouser expression and reveals a role of this gene in memory.

dGIPC is required for the locomotive activity and longevity in Drosophila

To identify genes that function in the adult neural system, we screened pools of P element-mediated mutants and tested locomotor activity of homozygous flies. Of 1014 P element-mutagenized lines, 638 were homozygous viable. These lines were tested for climbing ability and lifespan. We isolated dGIPC, a Drosophila homolog of GIPC, that produced a 50% premature loss of locomotor activity and a 30% reduction in life span. We found that dGIPC is expressed in the central brain of adult flies, especially in glia and dopaminergic (DA) neurons. Inhibition of dGIPC expression in DA neurons significantly affected climbing ability and survival. In vertebrates, interactions between GIPC with dopamine receptors have been reported. Our findings, together with those obtained from vertebrate models, suggest that DrosophiladGIPC acts in the adult central nervous system and may be required to regulate the trafficking of dopamine receptors needed for proper functioning of dopaminergic neurons.

A forward genetic screen in Drosophila implicates insulin signaling in age-related locomotor impairment

Age-related locomotor impairment (ARLI) is one of the most detrimental changes that occurs during aging. Elderly individuals with ARLI are at increased risks for falls, depression and a number of other co-morbidities. Despite its clinical significance, little is known about the genes that influence ARLI. We consequently performed a forward genetic screen to identify Drosophila strains with delayed ARLI using negative geotaxis as an index of locomotor function. One of the delayed ARLI strains recovered from the screen had a P-element insertion that decreased expression of the insulin signaling gene phosphoinositide-dependent kinase 1 (PDK1) Precise excision of the P-element insertion reverted PDK1 expression and ARLI to the same as control flies, indicating that disruption of PDK1 leads to delayed ARLI. Follow-up studies showed that additional loss of function mutations in PDK1 as well as loss of function alleles of two other insulin signaling genes, Dp110 and Akt (the genes for the catalytic subunit of phosphoinositide 3-kinase and AKT), also forestalled ARLI. Interestingly, only some of the strains with delayed ARLI had elevated resistance to paraquat, indicating that enhanced resistance to this oxidative stressor is not required for preservation of locomotor function across age. Our studies implicate insulin signaling as a key regulator of ARLI in Drosophila.

Bunched specifically regulates alpha/beta mushroom body neuronal cell proliferation during metamorphosis

In Drosophila, mushroom bodies are centers for higher order behavior. Mushroom body neurons consist of three distinct types of neuronal cells, alpha, alpha'/beta', and alpha/beta, which are all generated by the same neuroblasts. The mechanism by which a single neuroblast generates three different types of mushroom body neurons is a compelling area of research. Here, we report that bunched (bun) is expressed only in alpha/beta-type mushroom body neurons and that mutation of the bun gene only affects the development of alpha/beta neurons. Reduced bun expression causes decreased and premature arrest of neuroblast cell division, which results in reduced numbers of alpha/beta neurons and thin axon bundled formation. We propose that bun acts as a specific factor in regulating neuroblast mitotic activity during the development of alpha/beta neurons.

Genetic dissociation of ethanol sensitivity and memory formation in Drosophila melanogaster

The ad hoc genetic correlation between ethanol sensitivity and learning mechanisms in Drosophila could overemphasize a common process supporting both behaviors. To challenge directly the hypothesis that these mechanisms are singular, we examined the learning phenotypes of 10 new strains. Five of these have increased ethanol sensitivity, and the other 5 do not. We tested place and olfactory memory in each of these lines and found two new learning mutations. In one case, altering the tribbles gene, flies have a significantly reduced place memory, elevated olfactory memory, and normal ethanol response. In the second case, mutation of a gene we name ethanol sensitive with low memory (elm), place memory was not altered, olfactory memory was sharply reduced, and sensitivity to ethanol was increased. In sum, however, we found no overall correlation between ethanol sensitivity and place memory in the 10 lines tested. Furthermore, there was a weak but nonsignificant correlation between ethanol sensitivity and olfactory learning. Thus, mutations that alter learning and sensitivity to ethanol can occur independently of each other and this implies that the set of genes important for both ethanol sensitivity and learning is likely a subset of the genes important for either process.

DmOAZ, the unique Drosophila melanogaster OAZ homologue is involved in posterior spiracle development

In this paper, we study DmOAZ, the unique Drosophila melanogaster homologue of the OAZ zinc finger protein family. We show partial conservation of the zinc finger organization between DmOAZ and the vertebrate members of this family. We determine the exon/intron structure of the dmOAZ gene and deduce its open reading frame. Reverse transcriptase-polymerase chain reaction analysis shows that dmOAZ is transcribed throughout life. In the embryo, strongest DmOAZ expression is observed in the posterior spiracles. We suggest that dmOAZ acts as a secondary target of the Abd-B gene in posterior spiracle development, downstream of cut and ems. In a newly created loss-of-function mutant, dmOAZ ( 93 ), the "filzkörper" part of the posterior spiracles, is indeed structurally abnormal. The dmOAZ ( 93 ) mutant is a larval lethal, a phenotype that may be linked to the spiracular defect. Given the dmOAZ ( 93 ) mutant as a new tool, the fruit fly may provide an alternative model for analyzing in vivo the functions of OAZ family members.

DNase II deficiency impairs innate immune function in Drosophila

DNase II enzymes are highly conserved proteins that are required for the degradation of DNA within phagolysosomes. Engulfment of apoptotic cells and/or bacteria by phagocytic cells requires the function of DNase II to completely destroy ingested DNA. Mutation of the dnase II gene results in an increase of undegraded apoptotic DNA within phagocytic cells in mice and nematodes. Additionally, reduction of DNase II enzymatic activity in Drosophila melanogaster has been shown to lead to increased accumulation of DNA in the ovaries. Due to the importance of DNA clearance during infection, we hypothesized that a severe reduction of DNase II activity would result in diminished immune function and viability. To test this hypothesis, we knocked down DNase II activity in flies using RNAi. As expected, expression of a dnase II-RNAi construct in flies resulted in a dramatic reduction of DNase II activity and a significant decrease in total hemocyte numbers. Furthermore, infection of dnase II-RNAi flies with Gram negative or positive bacteria resulted in a severe reduction in fly viability. These results confirm that DNase II and the ability to clear macromolecular DNA is essential for maintaining proper immune function in Drosophila.

Drosophila Eph receptor guides specific axon branches of mushroom body neurons

The conserved Eph receptors and their Ephrin ligands regulate a number of developmental processes, including axon guidance. In contrast to the large vertebrate Eph/Ephrin family, Drosophila has a single Eph receptor and a single Ephrin ligand, both of which are expressed within the developing nervous system. Here, we show that Eph and Ephrin can act as a functional receptor-ligand pair in vivo. Surprisingly, and in contrast to previous results using RNA-interference techniques, embryos completely lacking Eph function show no obvious axon guidance defects. However, Eph/Ephrin signaling is required for proper development of the mushroom body. In wild type, mushroom body neurons bifurcate and extend distinct branches to different target areas. In Eph mutants, these neurons bifurcate normally, but in many cases the dorsal branch fails to project to its appropriate target area. Thus, Eph/Ephrin signaling acts to guide a subset of mushroom body branches to their correct synaptic targets.

Flexibility in a gene network affecting a simple behavior in Drosophila melanogaster

Gene interactions are emerging as central to understanding the realization of any phenotype. To probe the flexibility of interactions in a defined gene network, we isolated a set of 16 interacting genes in Drosophila, on the basis of their alteration of a quantitative behavioral phenotype-the loss of coordination in a temperature-sensitive allele of Syntaxin1A. The interactions inter se of this set of genes were then assayed in the presence and in the absence of the original Syntaxin1A mutation to ask whether the relationships among the 16 genes remain stable or differ after a change in genetic context. The pattern of epistatic interactions that occurs within this set of variants is dramatically altered in the two different genetic contexts. The results imply considerable flexibility in the network interactions of genes.

MKP-3 has essential roles as a negative regulator of the Ras/mitogen-activated protein kinase pathway during Drosophila development

Mitogen-activated protein kinase (MAPK) phosphatase 3 (MKP-3) is a well-known negative regulator in the Ras/extracellular signal-regulated kinase (ERK)-MAPK signaling pathway responsible for cell fate determination and proliferation during development. However, the physiological roles of MKP-3 and the mechanism by which MKP-3 regulates Ras/Drosophila ERK (DERK) signaling in vivo have not been determined. Here, we demonstrated that Drosophila MKP-3 (DMKP-3) is critically involved in cell differentiation, proliferation, and gene expression by suppressing the Ras/DERK pathway, specifically binding to DERK via the N-terminal ERK-binding domain of DMKP-3. Overexpression of DMKP-3 reduced the number of photoreceptor cells and inhibited wing vein differentiation. Conversely, DMKP-3 hypomorphic mutants exhibited extra photoreceptor cells and wing veins, and its null mutants showed striking phenotypes, such as embryonic lethality and severe defects in oogenesis. All of these phenotypes were highly similar to those of the gain-of-function mutants of DERK/rl. The functional interaction between DMKP-3 and the Ras/DERK pathway was further confirmed by genetic interactions between DMKP-3 loss-of-function mutants or overexpressing transgenic flies and various mutants of the Ras/DERK pathway. Collectively, these data provide the direct evidences that DMKP-3 is indispensable to the regulation of DERK signaling activity during Drosophila development.

Creation of EcR isoform-specific mutations in Drosophila melanogaster via local P element transposition, imprecise P element excision, and male recombination

Collections of single P transposable-element insertion strains that currently inactivate more than 25% of essential Drosophila genes have proven to be a valuable tool for genome research in Drosophila melanogaster. For genes unrepresented in these collections, strategies including local P element transposition and transposase-induced imprecise excision can be used to inactivate or delete the gene of interest. Here we report our use of local P element transposition followed by imprecise P element excision and transposase-induced male recombination to generate two deficiencies specific for the EcR-A isoform of the ecdysone receptor ( EcR) gene, and four larger deficiencies likely to affect multiple EcR functions. We also report here the determination of sequences flanking six EcR-B deficiencies generated in a previous imprecise excision screen. EcR-A encodes one of a family of three related nuclear receptor proteins that, together with the heterodimer partner USP, mediate ecdysone signaling during Drosophila development. Our results delineate sequences required in vivo for EcR-A function, as well as identifying EcR-A intron 1 sequences that are not essential for EcR function.

Octopamine receptor OAMB is required for ovulation in Drosophila melanogaster

Octopamine is a major monoamine in invertebrates and affects many physiological processes ranging from energy metabolism to complex behaviors. Octopamine binds to receptors located on various cell types and activates distinct signal transduction pathways to produce these diverse effects. We previously identified one of the Drosophila octopamine receptors named OAMB that produces increases in cAMP and intracellular Ca2+ upon ligand binding. It is expressed at high levels in the brain. To explore OAMB's physiological roles, we generated deletions in the OAMB locus. The resultant oamb mutants were viable without gross anatomical defects. The oamb females displayed normal courtship and copulation; however, they were impaired in ovulation with many mature eggs retained in their ovaries. RT-PCR, in situ hybridization, and expression of a reporter gene revealed that OAMB was also expressed in the thoracicoabdominal ganglion, the female reproductive system, and mature eggs in the ovary. Moreover, analysis of various alleles pinpointed the requirement for OAMB in the body, but not in the brain, for female fecundity. The novel expression pattern of OAMB and its genetic resource described in this study will help advance our understanding on how the neuromodulatory or endocrine system controls reproductive physiology and behavior.

Drosophila retinal homeobox (drx) is not required for establishment of the visual system, but is required for brain and clypeus development

The possibility that mechanisms of retinal determination may be similar between vertebrates and Drosophila has been supported by the observations that Pax6/eyeless genes are necessary and sufficient for retinal development. These studies suggest that the function of other gene families, operating during early eye development, might also be conserved. One candidate is the retinal homeobox (Rx) family of transcription factors. Vertebrate Rx is expressed in the prospective eye and forebrain and is required for eye morphogenesis, retinal precursor appearance, and normal forebrain development, indicating that it is an essential regulator of early eye and brain formation. Here, we test the hypothesis that Drosophila Rx (drx) is required for adult and larval eye development. We have isolated a drx null allele and demonstrate that the mutant compound eye and larval visual system is not detectably abnormal. However, we find that drx is required for development of a central brain structure, the ellipsoid body, suggesting that Rx function in the brain may be conserved. Finally, we characterize a novel anterior head phenotype and demonstrate that drx is required for clypeus development. Thus, our data suggest that drx may be required for the regulation of genes involved in brain morphogenesis and clypeus precursor development. We propose that differences in insect and vertebrate eye development may be explained by changes in gene regulation and/or the tissue of origin for eye precursor cells.

The clot gene of Drosophila melanogaster encodes a conserved member of the thioredoxin-like protein superfamily

The conversion of pyruvoyl-H(4)-pterin to pyrimidodiazepine (PDA), which is an essential step in the biosynthesis of the red components of Drosophila eye pigments known as drosopterins, requires the products of the genes sepia and clot. While the product of sepia has been shown to correspond to the enzyme PDA-synthase, the role of clot remains unknown, although the clot(1) allele was one of the first eye-color mutants to be isolated in Drosophila melanogaster,and much genetic and biochemical data has become available since. Here we report the cloning of the clot gene, describe its molecular organization and characterize the sequence alterations associated with the alleles cl(1) and cl(2). The coding properties of the gene show that it encodes a protein related to the Glutaredoxin class of the Thioredoxin-like enzyme superfamily, conserved members of which are found in human, mouse and plants. We suggest that the Clot protein is an essential component of a glutathione redox system required for the final step in the biosynthetic pathway for drosopterins.

Death to flies: Drosophila as a model system to study programmed cell death

Programmed cell death (PCD) is essential for the removal of unwanted cells and is critical for both restricting cell numbers and for tissue patterning during development. Components of the cell death machinery are remarkably conserved through evolution, from worms to mammals. Central to the PCD process is the family of cysteine proteases, known as caspases, which are activated by death-inducing signals. Comparisons between C. elegans and mammalian PCD have shown that there is additional complexity in the regulation of PCD in mammals. The fruitfly, Drosophila melanogaster, is proving an ideal genetically tractable model organism, of intermediary complexity between C. elegans and mammals, in which to study the intricacies of PCD. Here, we review the literature on PCD during Drosophila development, highlighting the methods used in these studies.

DEAF-1 function is essential for the early embryonic development of Drosophila

The Drosophila protein DEAF-1 is a sequence-specific DNA binding protein that was isolated as a putative cofactor of the Hox protein Deformed (Dfd). In this study, we analyze the effects of loss or gain of DEAF-1 function on Drosophila development. Maternal/zygotic mutations of DEAF-1 largely result in early embryonic arrest prior to the expression of zygotic segmentation genes, although a few embryos develop into larvae with segmentation defects of variable severity. Overexpression of DEAF-1 protein in embryos can induce defects in migration/closure of the dorsal epidermis, and overexpression in adult primordia can strongly disrupt the development of eye or wing. The DEAF-1 protein associates with many discrete sites on polytene chromosomes, suggesting that DEAF-1 is a rather general regulator of gene expression.

From sequence to phenotype: reverse genetics in Drosophila melanogaster

There has been a long history of innovation and development of tools for gene discovery and genetic analysis in Drosophila melanogaster. This includes methods to induce mutations and to screen for those mutations that disrupt specific processes, methods to map mutations genetically and physically, and methods to clone and characterize genes at the molecular level. Modern genetics also requires techniques to do the reverse to disrupt the functions of specific genes, the sequences of which are already known. This is the process referred to as reverse genetics. During recent years, some valuable new methods for conducting reverse genetics in Drosophila have been developed.

Of flies and men--studying human disease in Drosophila

During the past year, the Drosophila genome has been sequenced. More than 60% of genes implicated in human disease have Drosophila orthologues. Developments in RNA-mediated interference and homologous recombination have made 'reverse genetics' feasible in Drosophila. Conventional Drosophila genetics is being used increasingly to place human disease genes of unknown function in the context of functional pathways.

Screening insertion libraries for mutations in many genes simultaneously using DNA microarrays

We describe a method to screen pools of DNA from multiple transposon lines for insertions in many genes simultaneously. We use thermal asymmetric interlaced-PCR, a hemispecific PCR amplification protocol that combines nested, insertion-specific primers with degenerate primers, to amplify DNA flanking the transposons. In reconstruction experiments with previously characterized Arabidopsis lines carrying insertions of the maize Dissociation (Ds) transposon, we show that fluorescently labeled, transposon-flanking fragments overlapping ORFs hybridize to cognate expressed sequence tags (ESTs) on a DNA microarray. We further show that insertions can be detected in DNA pools from as many as 100 plants representing different transposon lines and that all of the tested, transposon-disrupted genes whose flanking fragments can be amplified individually also can be detected when amplified from the pool. The ability of a transposon-flanking fragment to hybridize declines rapidly with decreasing homology to the spotted DNA fragment, so that only ESTs with >90% homology to the transposon-disrupted gene exhibit significant cross-hybridization. Because thermal asymmetric interlaced-PCR fragments tend to be short, use of the present method favors recovery of insertions in and near genes. We apply the technique to screening pools of new Ds lines using cDNA microarrays containing ESTs for approximately 1,000 stress-induced and -repressed Arabidopsis genes.

Clonal analysis of cmp44E, which encodes a conserved putative transmembrane protein, indicates a requirement for cell viability in Drosophila

We have identified the cmp44E gene which encodes a putative multi-pass transmembrane protein that is conserved from yeast to humans. The expression of cmp44E during embryogenesis is ubiquitous with notably higher levels in the CNS and brain. It is also expressed in the germline during the germarial stages as well as several later stages of oogenesis. Utilizing a P-element insertion at the 5' end of cmp44E we have isolated several deletions, created by imprecise excision events which eliminate most or all of its coding region. Analysis of these deficiencies has revealed that cmp44E is an essential gene required for embryogenesis. Results obtained from germline clone analysis indicate that cmp44E is not only required in the germline slem cells early in oogenesis, but is also required in other tissues probably due to it being required for cell viability. Finally, using germline transformation, we have identified a minimal genomic fragment capable of fully rescuing a null allele of cmp44E.

Reversal of fortune for Drosophila geneticists?

Although Drosophila is a wonderful model organism, there is one molecular arena where it lags far behind its yeast and mouse model counterparts. Reverse genetics, whereby a piece of DNA is integrated into a target gene such that the gene is disrupted or replaced, is not easy in Drosophila. As Engels explains in his provocative Perspective, this may be set to change with the description of a new method for reverse genetics in Drosophila (Rong and Golic). This new technique should ensure that Drosophila remains the darling of geneticists for many years to come.

Nested chromosomal deletions induced with retroviral vectors in mice

Chromosomal deletions, especially nested deletions, are major genetic tools in diploid organisms that facilitate the functional analysis of large chromosomal regions and allow the rapid localization of mutations to specific genetic intervals. In mice, well-characterized overlapping deletions are only available at a few chromosomal loci, partly due to drawbacks of existing methods. Here we exploit the random integration of a retrovirus to generate high-resolution sets of nested deletions around defined loci in embryonic stem (ES) cells, with sizes extending from a few kilobases to several megabases. This approach expands the application of Cre-loxP-based chromosome engineering because it not only allows the construction of hundreds of overlapping deletions, but also provides molecular entry points to regions based on the retroviral tags. Our approach can be extended to any region of the mouse genome.

Requirement of RBP9, a Drosophila Hu homolog, for regulation of cystocyte differentiation and oocyte determination during oogenesis

The Drosophila RNA binding protein RBP9 and its Drosophila and human homologs, ELAV and the Hu family of proteins, respectively, are highly expressed in the nuclei of neuronal cells. However, biochemical studies suggest that the Hu proteins function in the regulation of mRNA stability, which occurs in the cytoplasm. In this paper, we show that RBP9 is expressed not only in the nuclei of neuronal cells but also in the cytoplasm of cystocytes during oogenesis. Despite the predominant expression of RBP9 in nerve cells, mutational analysis revealed a female sterility phenotype rather than neuronal defects for Rbp9 mutants. The female sterility phenotype of the Rbp9 mutants resulted from defects in oogenesis; the lack of Rbp9 activity caused the germarium region of the mutants to be filled with undifferentiated cystocytes. RBP9 appears to stimulate cystocyte differentiation by regulating the expression of bag-of-marbles (bam) mRNA, which encodes a developmental regulator of germ cells. RBP9 protein bound specifically to bam mRNA in vitro, which is required for cystocyte proliferation, and the number of cells that expressed BAM protein was increased 5- to 10-fold in the germarium regions of Rbp9 mutants. These results suggest that RBP9 protein binds to bam mRNA to down regulate BAM protein expression, which is essential for the initiation of cystocyte differentiation into functional egg chambers. In hypomorphic Rbp9 mutants, cystocytes differentiated into egg chambers; however, oocyte determination and positioning were perturbed. Therefore, the concentrated localization of RBP9 protein in the oocyte of the early egg chambers may be required for proper oocyte determination or positioning.

The role of RBF in the introduction of G1 regulation during Drosophila embryogenesis

The first appearance of G1 during Drosophila embryogenesis, at cell cycle 17, is accompanied by the down-regulation of E2F-dependent transcription. Mutant alleles of rbf were generated and analyzed to determine the role of RBF in this process. Embryos lacking both maternal and zygotic RBF products show constitutive expression of PCNA and RNR2, two E2F-regulated genes, indicating that RBF is required for their transcriptional repression. Despite the ubiquitous expression of E2F target genes, most epidermal cells enter G1 normally. Rather than pausing in G1 until the appropriate time for cell cycle progression, many of these cells enter an ectopic S-phase. These results indicate that the repression of E2F target genes by RBF is necessary for the maintenance but not the initiation of a G1 phase. The phenotype of RBF-deficient embryos suggests that rbf has a function that is complementary to the roles of dacapo and fizzy-related in the introduction of G1 during Drosophila embryogenesis.

Dissatisfaction encodes a tailless-like nuclear receptor expressed in a subset of CNS neurons controlling Drosophila sexual behavior

The dissatisfaction (dsf) gene is necessary for appropriate sexual behavior and sex-specific neural development in both sexes. dsf males are bisexual and mate poorly, while mutant females resist male courtship and fail to lay eggs. Males and females have sex-specific neural abnormalities. We have cloned dsf and rescued both behavioral and neural phenotypes. dsf encodes a nuclear receptor closely related to the vertebrate Tailless proteins and is expressed in both sexes in an extremely limited set of neurons in regions of the brain potentially involved in sexual behavior. Expression of a female transformer cDNA under the control of a dsf enhancer in males leads to dsf-like bisexual behavior.

Wrapper, a novel member of the Ig superfamily, is expressed by midline glia and is required for them to ensheath commissural axons in Drosophila

The midline glia are specialized, nonneuronal cells at the midline of the Drosophila central nervous system (CNS). During development, the midline glia provide guidance cues for extending axons. At the same time, they migrate and help separate the two axon commissures. They then wrap around and ensheath the commissural axons. In many segments, a few of the glia do not enwrap the axons, and these cells die. The wrapper gene encodes a novel member of the immunoglobulin (Ig) superfamily. Wrapper protein is expressed specifically on the surface of midline glia. In wrapper mutant embryos, the midline glia express their normal guidance cues and migrate normally. However, they do not ensheath the commissural axons, and as a result, the glia die. In the absence of Wrapper, the two axon commissures are not properly separated.

Molecular screening for P-element insertions in a large genomic region of Drosophila melanogaster using polymerase chain reaction mediated by the vectorette

As an alternative to existing methods for the detection of new insertions during a transposon mutagenesis, we adapted the method of vectorette ligation to genomic restriction fragments followed by PCR to obtain genomic sequences flanking the transposon. By combining flies containing a defined genomic transposon with an excess of flies containing unrelated insertion sites, we demonstrate the specificity and sensitivity of the procedure in the detection of integration events. This method was applied in a transposon-tagging screen for BJ1, the Drosophila homolog of the vertebrate gene Regulator of Chromosome Condensation (RCCI). Genetic mobilization of a single genomic P element was used to generate preferentially new local insertions from which integrations into a genomic region surrounding the BJ1 gene were screened. Flies harboring new insertions were phenotypically selected on the basis of the zeste1-dependent transvection of white. We detected a single transposition to a 13-kb region close to the BJ1 gene among 6650 progeny that were analyzed. Southern analysis of the homozygous line confirmed the integration 3 kb downstream of BJ1.

Kinesin light chains are essential for axonal transport in Drosophila

Kinesin is a heterotetramer composed of two 115-kD heavy chains and two 58-kD light chains. The microtubule motor activity of kinesin is performed by the heavy chains, but the functions of the light chains are poorly understood. Mutations were generated in the Drosophila gene Kinesin light chain (Klc), and the phenotypic consequences of loss of Klc function were analyzed at the behavioral and cellular levels. Loss of Klc function results in progressive lethargy, crawling defects, and paralysis followed by death at the end of the second larval instar. Klc mutant axons contain large aggregates of membranous organelles in segmental nerve axons. These aggregates, or organelle jams (Hurd, D.D., and W.M. Saxton. 1996. Genetics. 144: 1075-1085), contain synaptic vesicle precursors as well as organelles that may be transported by kinesin, kinesin-like protein 68D, and cytoplasmic dynein, thus providing evidence that the loss of Klc function blocks multiple pathways of axonal transport. The similarity of the Klc and Khc (. Cell 64:1093-1102; Hurd, D.D., and W.M. Saxton. 1996. Genetics 144: 1075-1085) mutant phenotypes indicates that KLC is essential for kinesin function, perhaps by tethering KHC to intracellular cargos or by activating the kinesin motor.

The Drosophila tango gene encodes a bHLH-PAS protein that is orthologous to mammalian Arnt and controls CNS midline and tracheal development

The Drosophila single-minded and trachealess bHLH-PAS genes control transcription and development of the CNS midline cell lineage and tracheal tubules, respectively. We show that Single-minded and Trachealess activate transcription by forming dimers with the Drosophila Tango protein that is an orthologue of the mammalian Arnt protein. Both cell culture and in vivo studies show that a DNA enhancer element acts as a binding site for both Single-minded::Tango and Trachealess::Tango heterodimers and functions in controlling CNS midline and tracheal transcription. Isolation and analysis of tango mutants reveal CNS midline and tracheal defects, and gene dosage studies demonstrate in vivo interactions between single-minded::tango and trachealess::tango. These experiments support the existence of an evolutionarily conserved, functionally diverse bHLH-PAS protein regulatory system.

Biological characterization of Drosophila Rapgap1, a GTPase activating protein for Rap1

The activity of Ras family proteins is modulated in vivo by the function of GTPase activating proteins, which increase their intrinsic rate of GTP hydrolysis. We have isolated cDNAs encoding a GAP for the Drosophila Rap1 GTPase. Drosophila Rapgap1 encodes an 850-amino acid protein with a central region that displays substantial sequence similarity to human RapGAP. This domain, when expressed in Escherichia coli, potently stimulates Rap1 GTPase activity in vitro. Unlike Rap1, which is ubiquitously expressed, Rapgap1 expression is highly restricted. Rapgap1 is expressed at high levels in the developing photoreceptor cells and in the optic lobe. Rapgap1 mRNA is also localized in the pole plasm in an oskar-dependent manner. Although mutations that completely abolish Rapgap1 function display no obvious phenotypic abnormalities, overexpression of Rapgap1 induces a rough eye phenotype that is exacerbated by reducing Rap1 gene dosage. Thus, Rapgap1 can function as a negative regulator of Rap1-mediated signaling in vivo.

Rescue of a Drosophila NF1 mutant phenotype by protein kinase A

The neurofibromatosis type 1 (NF1) tumor suppressor protein is thought to restrict cell proliferation by functioning as a Ras-specific guanosine triphosphatase-activating protein. However, Drosophila homozygous for null mutations of an NF1 homolog showed no obvious signs of perturbed Ras1-mediated signaling. Loss of NF1 resulted in a reduction in size of larvae, pupae, and adults. This size defect was not modified by manipulating Ras1 signaling but was restored by expression of activated adenosine 3', 5'-monophosphate-dependent protein kinase (PKA). Thus, NF1 and PKA appear to interact in a pathway that controls the overall growth of Drosophila.

Genetic analysis of myoblast fusion: blown fuse is required for progression beyond the prefusion complex

The events of myoblast fusion in Drosophila are dissected here by combining genetic analysis with light and electron microscopy. We describe a new and essential intermediate step in the process, the formation of a prefusion complex consisting of "paired vesicles." These pairs of vesicles from different cells align with each other across apposed plasma membranes. This prefusion complex resolves into dense membrane plaques between apposed cells; these cells then establish cytoplasmic continuity by fusion of small areas of plasma membrane followed by vesiculation of apposed membranes. Different steps in this process are specifically blocked by mutations in four genes required for myoblast fusion. One of these genes, blown fuse, encodes a novel cytoplasmic protein expressed in unfused myoblasts that is essential for progression beyond the prefusion complex stage.

Molecular and genetic analyses of lama, an evolutionarily conserved gene expressed in the precursors of the Drosophila first optic ganglion

Drosophila retinal axons trigger both the proliferation of their targets, the lamina neurons, as well as the final differentiation and migration of the lamina glia. To date, the molecular basis of these interactions has remained unclear. We have identified a new gene, lamina ancestor (lama). Both the lamina's neural and glial progenitors express lama, even though these cells have very different developmental origins. Expression of lama is down-regulated once the precursors begin their differentiation programs. Loss of function mutants are viable and fertile, and appear to have normally developed visual systems. lama encodes a novel protein that is 74% identical to its D. virilis homologue.

A neural tetraspanin, encoded by late bloomer, that facilitates synapse formation

Upon contacting its postsynaptic target, a neuronal growth cone transforms into a presynaptic terminal. A membrane component on the growth cone that facilitates synapse formation was identified by means of a complementary DNA-based screen followed by genetic analysis. The late bloomer (lbl) gene in Drosophila encodes a member of the tetraspanin family of cell surface proteins. LBL protein is transiently expressed on motor axons, growth cones, and terminal arbors. In lbl mutant embryos, the growth cone of the RP3 motoneuron contacts its target muscles, but synapse formation is delayed and neighboring motoneurons display an increase in ectopic sprouting.

Receptor tyrosine phosphatases are required for motor axon guidance in the Drosophila embryo

The receptor tyrosine phosphatases DPTP69D and DPTP99A are expressed on motor axons in Drosophila embryos. In mutant embryos lacking DPTP69D protein, motor neuron growth cones stop growing before reaching their muscle targets, or follow incorrect pathways that bypass these muscles. Mutant embryos lacking DPTP99A are indistinguishable from wild type. Motor axon defects in dptp69D dptp99A double mutant embryos, however, are much more severe than in embryos lacking only DPTP69D. Our results demonstrate that DPTP69D and DPTP99A are required for motor axon guidance and that they have partially redundant functions during development of the neuro-muscular system.