P-element insertion alleles of essential genes on the third chromosome of Drosophila melanogaster: correlation of physical and cytogenetic maps in chromosomal region 86E-87F

A novel insertional allele of the CG18135 gene is associated with severe mutant phenotypes in Drosophila melanogaster

Drosophila melanogaster has been at the forefront of genetic studies and biochemical modeling for over a century. Yet, the functions of many genes are still unknown, mainly because no phenotypic data are available. Herein, we present the first evidence data regarding the particular molecular and other quantifiable phenotypes, such as viability and anatomical anomalies, induced by a novel P{lacW} insertional mutant allele of the CG18135 gene. So far, the CG18135 functions have only been theorized based on electronic annotation and presumptive associations inferred upon high-throughput proteomics or RNA sequencing experiments. The descendants of individuals harboring the CG18135 P{lacW}CG18135 allele were scored in order to assess mutant embryonic, larval, and pupal viability versus Canton Special (CantonS). Our results revealed that the homozygous CG18135 P{lacW}CG18135 /CG18135 P{lacW}CG18135 genotype determines significant lethality both at the inception of the larval stage and during pupal development. The very few imago escapers that either breach or fully exit the puparium exhibit specific eye depigmentation, wing abnormal unfolding, strong locomotor impairment with apparent spasmodic leg movements, and their maximum lifespan is shorter than 2 days. Using the quantitative real-time PCR (qRT-PCR) method, we found that CG18135 is upregulated in male flies, but an unexpected gene upregulation was also detected in heterozygous mutants compared to wild-type flies, probably because of regulatory perturbations induced by the P{lacW} transposon. Our work provides the first phenotypic evidence for the essential role of CG18135, a scenario in accordance with the putative role of this gene in carbohydrate-binding processes.

Mutations of γCOP Gene Disturb Drosophila melanogaster Innate Immune Response to Pseudomonas aeruginosa

Drosophila melanogaster (the fruit fly) is a valuable experimental platform for modeling host–pathogen interactions. It is also commonly used to define innate immunity pathways and to understand the mechanisms of both host tolerance to commensal microbiota and response to pathogenic agents. Herein, we investigate how the host response to bacterial infection is mirrored in the expression of genes of Imd and Toll pathways when D. melanogaster strains with different γCOP genetic backgrounds are infected with Pseudomonas aeruginosa ATCC 27853. Using microarray technology, we have interrogated the whole-body transcriptome of infected versus uninfected fruit fly males with three specific genotypes, namely wild-type Oregon, γCOP^S057302/TM6B and γCOP^14a/γCOP^14a. While the expression of genes pertaining to Imd and Toll is not significantly modulated by P. aeruginosa infection in Oregon males, many of the components of these cascades are up- or downregulated in both infected and uninfected γCOP^S057302/TM6B and γCOP^14a/γCOP^14a males. Thus, our results suggest that a γCOP genetic background modulates the gene expression profiles of Imd and Toll cascades involved in the innate immune response of D. melanogaster, inducing the occurrence of immunological dysfunctions in γCOP mutants.

Poly(ADP-ribose) polymerase 1 in genome-wide expression control in Drosophila

Poly(ADP-ribose) polymerase 1 (PARP-1) is a nuclear enzyme involved in DNA repair and transcription regulation, among other processes. Malignant transformations, tumor progression, the onset of some neuropathies and other disorders have been linked to misregulation of PARP-1 activity. Despite intensive studies during the last few decades, the role of PARP-1 in transcription regulation is still not well understood. In this study, a transcriptomic analysis in Drosophila melanogaster third instar larvae was carried out. A total of 602 genes were identified, showing large-scale changes in their expression levels in the absence of PARP-1 in vivo. Among these genes, several functional gene groups were present, including transcription factors and cytochrome family members. The transcription levels of genes from the same functional group were affected by the absence of PARP-1 in a similar manner. In the absence of PARP-1, all misregulated genes coding for transcription factors were downregulated, whereas all genes coding for members of the cytochrome P450 family were upregulated. The cytochrome P450 proteins contain heme as a cofactor and are involved in oxidoreduction. Significant changes were also observed in the expression of several mobile elements in the absence of PARP-1, suggesting that PARP-1 may be involved in regulating the expression of mobile elements.

Genomic identification and functional analysis of essential genes in Caenorhabditis elegans

Background

Essential genes are required for an organism’s viability and their functions can vary greatly, spreading across many pathways. Due to the importance of essential genes, large scale efforts have been undertaken to identify the complete set of essential genes and to understand their function. Studies of genome architecture and organization have found that genes are not randomly disturbed in the genome.

Results

Using combined genetic mapping, Illumina sequencing, and bioinformatics analyses, we successfully identified 44 essential genes with 130 lethal mutations in genomic regions of C. elegans of around 7.3 Mb from Chromosome I (left). Of the 44 essential genes, six of which were genes not characterized previously by mutant alleles, let-633/let-638 (B0261.1), let-128 (C53H9.2), let-511 (W09C3.4), let-162 (Y47G6A.18), let-510 (Y47G6A.19), and let-131 (Y71G12B.6). Examine essential genes with Hi-C data shows that essential genes tend to cluster within TAD units rather near TAD boundaries. We have also shown that essential genes in the left half of chromosome I in C. elegans function in enzyme and nucleic acid binding activities during fundamental processes, such as DNA replication, transcription, and translation. From protein-protein interaction networks, essential genes exhibit more protein connectivity than non-essential genes in the genome. Also, many of the essential genes show strong expression in embryos or early larvae stages, indicating that they are important to early development.

Conclusions

Our results confirmed that this work provided a more comprehensive picture of the essential gene and their functional characterization. These genetic resources will offer important tools for further heath and disease research.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5251-3) contains supplementary material, which is available to authorized users.

Genome-Wide Screen for New Components of the Drosophila melanogaster Torso Receptor Tyrosine Kinase Pathway

Patterning of the Drosophila embryonic termini by the Torso (Tor) receptor pathway has long served as a valuable paradigm for understanding how receptor tyrosine kinase signaling is controlled. However, the mechanisms that underpin the control of Tor signaling remain to be fully understood. In particular, it is unclear how the Perforin-like protein Torso-like (Tsl) localizes Tor activity to the embryonic termini. To shed light on this, together with other aspects of Tor pathway function, we conducted a genome-wide screen to identify new pathway components that operate downstream of Tsl. Using a set of molecularly defined chromosomal deficiencies, we screened for suppressors of ligand-dependent Tor signaling induced by unrestricted Tsl expression. This approach yielded 59 genomic suppressor regions, 11 of which we mapped to the causative gene, and a further 29 that were mapped to <15 genes. Of the identified genes, six represent previously unknown regulators of embryonic Tor signaling. These include twins (tws), which encodes an integral subunit of the protein phosphatase 2A complex, and α-tubulin at 84B (αTub84B), a major constituent of the microtubule network, suggesting that these may play an important part in terminal patterning. Together, these data comprise a valuable resource for the discovery of new Tor pathway components. Many of these may also be required for other roles of Tor in development, such as in the larval prothoracic gland where Tor signaling controls the initiation of metamorphosis.

The function of Drosophila larval class IV dendritic arborization sensory neurons in the larval-pupal transition is separable from their function in mechanical nociception responses

The sensory and physiological inputs which govern the larval-pupal transition in Drosophila, and the neuronal circuity that integrates them, are complex. Previous work from our laboratory identified a dosage-sensitive genetic interaction between the genes encoding the Rho-GEF Trio and the zinc-finger transcription factor Sequoia that interfered with the larval-pupal transition. Specifically, we reported heterozygous mutations in sequoia (seq) dominantly exacerbated the trio mutant phenotype, and this seq-enhanced trio mutant genotype blocked the transition of third instar larvae from foragers to wanderers, a requisite behavioral transition prior to pupation. In this work, we use the GAL4-UAS system to rescue this phenotype by tissue-specific trio expression. We find that expressing trio in the class IV dendritic arborization (da) sensory neurons rescues the larval-pupal transition, demonstrating the reliance of the larval-pupal transition on the integrity of these sensory neurons. As nociceptive responses also rely on the functionality of the class IV da neurons, we test mechanical nociceptive responses in our mutant and rescued larvae and find that mechanical nociception is separable from the ability to undergo the larval-pupal transition. This demonstrates for the first time that the roles of the class IV da neurons in governing two critical larval behaviors, the larval-pupal transition and mechanical nociception, are functionally separable from each other.

Phenotypes Associated with Second Chromosome P Element Insertions in Drosophila melanogaster

In Drosophila melanogaster, P element transposition has been a productive means of insertional mutagenesis. Thousands of genes have been tagged with natural and engineered P element constructs. Nevertheless, chromosomes carrying P element insertions tend to have high levels of background mutations from P elements inserting and excising during transposition. Consequently, the phenotypes seen when P element-bearing chromosomes are homozygous are often not attributable to the P insertions themselves. In this study, 178 strains in the Bloomington Drosophila Stock Center collection with P insertions on the second chromosome were complementation tested against molecularly defined chromosomal deletions and previously characterized single-gene mutations to determine if recessive lethality or sterility is associated with the P insertions rather than background mutations. This information should prove valuable to geneticists using these strains for experimental studies of gene function.

LIMK Regulates Tumor-Cell Invasion and Matrix Degradation Through Tyrosine Phosphorylation of MT1-MMP

During their metastatic spread, cancer cells need to remodel the extracellular matrix in order to migrate through stromal compartments adjacent to the primary tumor. Dissemination of breast carcinoma cells is mediated by membrane type 1-matrix metalloproteinase (MT1-MMP/MMP14), the main invadopodial matrix degradative component. Here, we identify MT1-MMP as a novel interacting partner of dual-specificity LIM Kinase-1 and -2 (LIMK1/2), and provide several evidence for phosphorylation of tyrosine Y573 in the cytoplasmic domain of MT1-MMP by LIMK. Phosphorylation of Y573 influences association of F-actin binding protein cortactin to MT1-MMP-positive endosomes and invadopodia formation and matrix degradation. Moreover, we show that LIMK1 regulates cortactin association to MT1-MMP-positive endosomes, while LIMK2 controls invadopodia-associated cortactin. In turn, LIMK1 and LIMK2 are required for MT1-MMP-dependent matrix degradation and cell invasion in a three-dimensional type I collagen environment. This novel link between LIMK1/2 and MT1-MMP may have important consequences for therapeutic control of breast cancer cell invasion.

Morphological characterization and molecular mapping of an irradiation-induced Speckled mutant in the silkworm, Bombyx mori

Speckled (Spc), an X-ray-induced lethal mutant of Bombyx mori, exhibits a mosaic dark-brown-spotted larval epidermis in both sexes and egg-laying problems only in females. Here, we report the morphological characterization and molecular mapping of the Spc mutant. Morphological investigations revealed that the epidermal ultrastructure of the small, dark-brown spots was more dense than that of the white regions in both Spc/+ mutants and wild type, and that the lethality of the Spc/Spc mutants occurred during early embryogenesis. Furthermore, the ovarioles and ovipositor were disconnected in approximately 85.5% of Spc/+ females, a further 2.5% had a connection between the ovarioles and ovipositor that was too narrow to lay eggs. The remaining females showed a normal connection similar to that of the wild type. We successfully narrowed down the location of the Spc mutation to a region on chromosome 4 that was ∼1041 kb long. Gene-prediction analysis identified 25 candidate genes in this region. Chromosome structure analysis indicated that a ∼305 kb deletion was included in the mapping region. Temporal and spatial reverse transcription PCR (RT-PCR) analysis showed that several genes in the mapped region are associated with the Spc mutant. Although the genes responsible for the Spc mutation were not definitively identified, our results further the current understanding of the complex mechanism underlying the multiple morphological defects in Spc mutants.

Animal Models to Study AMPK

AMPK is an evolutionary conserved energy sensor involved in the regulation of energy metabolism. Based on biochemical studies, AMPK has brought much of interest in recent years due to its potential impact on metabolic disorders. Suitable animal models are therefore essential to promote our understanding of the molecular and functional roles of AMPK but also to bring novel information for the development of novel therapeutic strategies. The organism systems include pig (Sus scrofa), mouse (Mus musculus), fly (Drosophila melanogaster), worm (Caenorhabditis elegans), and fish (Danio rerio) models. These animal models have provided reliable experimental evidence demonstrating the crucial role of AMPK in the regulation of metabolism but also of cell polarity, autophagy, and oxidative stress. In this chapter, we update the new development in the generation and application of animal models for the study of AMPK biology. We also discuss recent breakthroughs from studies in mice, flies, and worms showing how AMPK has a primary role in initiating or promoting pathological or beneficial impact on health.

Towards a compendium of essential genes - From model organisms to synthetic lethality in cancer cells

Essential genes are defined by their requirement to sustain life in cells or whole organisms. The systematic identification of essential gene sets not only allows insights into the fundamental building blocks of life, but may also provide novel therapeutic targets in oncology. The discovery of essential genes has been tightly linked to the development and deployment of various screening technologies. Here, we describe how gene essentiality was addressed in different eukaryotic model organisms, covering a range of organisms from yeast to mouse. We describe how increasing knowledge of evolutionarily divergent genomes facilitate identification of gene essentiality across species. Finally, the impact of gene essentiality and synthetic lethality on cancer research and the clinical translation of screening results are highlighted.

Polo-mediated phosphorylation of Maelstrom regulates oocyte determination during oogenesis in Drosophila

In Drosophila, Maelstrom is a conserved component of the perinuclear nuage, a germline-unique structure that appears to serve as a site for Piwi-interacting RNA (piRNA) production to repress deleterious transposons. Maelstrom also functions in the nucleus as a transcriptional regulator to repress the expression of microRNA-7, a process that is essential for the proper differentiation of germline stem cells. In this paper, we report another function of Maelstrom in regulating oocyte determination independently of its transposon silencing and germline stem cell differentiation activities. In Drosophila, the conserved serine 138 residue in Maelstrom is required for its phosphorylation, an event that promotes oocyte determination. Phosphorylation of Maelstrom is required for the repression of the pachytene checkpoint protein Sir2, but not for transposon silencing or for germline stem cell differentiation. We identify Polo as a kinase that mediates the phosphorylation of Maelstrom. Our results suggest that the Polo-mediated phosphorylation of Maelstrom may be a mechanism that controls oocyte determination by inactivating the pachytene checkpoint via the repression of Sir2 in Drosophila ovaries.

On the genetic parameter determining the efficiency of purging: an estimate for Drosophila egg-to-pupae viability

The consequences of inbreeding on fitness can be crucial in evolutionary and conservation grounds and depend upon the efficiency of purging against deleterious recessive alleles. Recently, analytical expressions have been derived to predict the evolution of mean fitness, taking into account both inbreeding and purging, which depend on an 'effective purging coefficient (d(e) )'. Here, we explore the validity of that predictive approach and assay the strength of purging by estimating d(e) for egg-to-pupae viability (EPV) after a drastic reduction in population size in a recently captured base population of Drosophila melanogaster. For this purpose, we first obtained estimates of the inbreeding depression rate (δ) for EPV in the base population, and we found that about 40% was due to segregating recessive lethals. Then, two sets of lines were founded from this base population and were maintained with different effective size throughout the rest of the experiment (N = 6; N = 12), their mean EPV being assayed at different generations. Due to purging, the reductions in mean EPV experienced by these lines were considerably smaller than the corresponding neutral predictions. For the 60% of δ attributable to nonlethal deleterious alleles, our results suggest an effective purging coefficient d(e) > 0.02. Similarly, we obtain that d(e) > 0.09 is required to roughly account for purging against the pooled inbreeding depression from lethal and nonlethal deleterious alleles. This implies that purging should be efficient for population sizes of the order of a few tens and larger, but might be inefficient against nonlethal deleterious alleles in smaller populations.

Ash2 acts as an ecdysone receptor coactivator by stabilizing the histone methyltransferase Trr

The molting hormone ecdysone triggers chromatin changes via histone modifications that are important for gene regulation. On hormone activation, the ecdysone receptor (EcR) binds to the SET domain-containing histone H3 methyltransferase trithorax-related protein (Trr). Methylation of histone H3 at lysine 4 (H3K4me), which is associated with transcriptional activation, requires several cofactors, including Ash2. We find that ash2 mutants have severe defects in pupariation and metamorphosis due to a lack of activation of ecdysone-responsive genes. This transcriptional defect is caused by the absence of the H3K4me3 marks set by Trr in these genes. We present evidence that Ash2 interacts with Trr and is required for its stabilization. Thus we propose that Ash2 functions together with Trr as an ecdysone receptor coactivator.

Exploiting Drosophila genetics to understand microRNA function and regulation

Although a great deal is known about the identity, biogenesis, and targeting capacity of microRNAs (miRNAs) in animal cells, far less is known about their functional requirements at the organismal level. Much remains to be understood about the necessity of miRNAs for overt phenotypes, the identity of critical miRNA targets, and the control of miRNA transcription. In this review, we provide an overview of genetic strategies to study miRNAs in the Drosophila system, including loss- and gain-of-function techniques, genetic interaction strategies, and transgenic reporters of miRNA expression and activity. As we illustrate the usage of these techniques in intact Drosophila, we see certain recurrent themes for miRNA functions, including energy homeostasis, apoptosis suppression, growth control, and regulation of core cell signaling pathways. Overall, we hope that this exposition of Drosophila genetic techniques, well known to the legions of fly geneticists and used to study all genes, can inform the general miRNA community that focuses on other biochemical, molecular, computational, and structural avenues. Clearly, it is the combination of these myriad techniques that has accelerated miRNA research to its extraordinary pace.

Drosophila basement membrane collagen col4a1 mutations cause severe myopathy

Recent data from clinical and mammalian genetic studies indicate that COL4A1 mutations manifest with basement membrane defects that result in muscle weakness, cramps, contractures, dystrophy and atrophy. In-depth studies of mutant COL4A1-associated muscle phenotype, however, are lacking and significant details of the muscle-specific pathomechanisms remain unknown. In this study, we have used a comprehensive set of Drosophila col4a1 and col4a2 mutants and a series of genetic and mutational analyses, gene, protein expression, and immunohistochemistry experiments in order to establish a Drosophila model and address some of these questions. The Drosophila genome contains two type IV collagen genes, col4a1 and col4a2. Mutant heterozygotes of either gene are viable and fertile, whereas homozygotes are lethal. In complementation analysis of all known mutants of the locus and a complementation matrix derived from these data we have identified the dominant lesions within the col4a1, but not within the col4a2 gene. Expression of a col4a1 transgene partially rescued the dominant and recessive mutant col4a1 alleles but not the col4a2 mutations that were all recessive. Partial complementation suggested that col4a1 gene mutations have strong antimorph effect likely due to the incorporation of the mutant protein into the triple helix. In col4a1 mutants, morphological changes of the oviduct muscle included severe myopathy with centronuclear myofibers leading to gradual development of female sterility. In larval body wall muscles ultrastructural changes included disturbance of A and I bands between persisting Z bands. In the most severely affected DTS-L3 mutant, we have identified four missense mutations within the coding region of the col4a1 gene two of which affected the Y within the Gly-X-Y unit and a 3' UTR point mutation. In conclusion, our Drosophila mutant series may serve as an effective model to uncover the mechanisms by which COL4A1 mutations result in compromised myofiber-basement membrane interactions and aberrant muscle function.

Suppression of scant identifies Endos as a substrate of greatwall kinase and a negative regulator of protein phosphatase 2A in mitosis

Protein phosphatase 2A (PP2A) plays a major role in dephosphorylating the targets of the major mitotic kinase Cdk1 at mitotic exit, yet how it is regulated in mitotic progression is poorly understood. Here we show that mutations in either the catalytic or regulatory twins/B55 subunit of PP2A act as enhancers of gwl^Scant, a gain-of-function allele of the Greatwall kinase gene that leads to embryonic lethality in Drosophila when the maternal dosage of the mitotic kinase Polo is reduced. We also show that heterozygous mutant endos alleles suppress heterozygous gwl^Scant; many more embryos survive. Furthermore, heterozygous PP2A mutations make females heterozygous for the strong mutation polo¹¹ partially sterile, even in the absence of gwl^Scant. Heterozygosity for an endos mutation suppresses this PP2A/polo¹¹ sterility. Homozygous mutation or knockdown of endos leads to phenotypes suggestive of defects in maintaining the mitotic state. In accord with the genetic interactions shown by the gwl^Scant dominant mutant, the mitotic defects of Endos knockdown in cultured cells can be suppressed by knockdown of either the catalytic or the Twins/B55 regulatory subunits of PP2A but not by the other three regulatory B subunits of Drosophila PP2A. Greatwall phosphorylates Endos at a single site, Ser68, and this is essential for Endos function. Together these interactions suggest that Greatwall and Endos act to promote the inactivation of PP2A-Twins/B55 in Drosophila. We discuss the involvement of Polo kinase in such a regulatory loop.

Progression through mitosis requires the addition of phosphate groups onto specific proteins by enzymes collectively known as mitotic protein kinases. At the end of mitosis, these phosphates are removed by protein phosphatases. Whereas we know quite a lot about the mitotic protein kinases, we know much less about the phosphatases. Here we used the fruit fly Drosophila as a model organism to identify a pathway regulating a phosphatase required for mitotic exit. Using mutations in genes for this pathway in the fly and by depleting levels of corresponding proteins from cultured cells, we established the relationships between the gene products. This has revealed that Greatwall mitotic kinase works in concert with the protein Endos to antagonise Protein Phosphatase 2A (PP2A). Specifically, Greatwall and Endos affect the activity of a particular form of PP2A that is associated with only one of the four different regulatory subunits found in Drosophila. We found that phosphorylation of Endos at a defined position by Greatwall kinase is required for its function. Together this provides genetic evidence that the Greatwall mitotic kinase inhibits the PP2A phosphatase required for mitotic exit thus complementing biochemical experiments using frog eggs and indicating the universality of this mechanism.

Drosophila Ten-m and filamin affect motor neuron growth cone guidance

The Drosophila Ten-m (also called Tenascin-major, or odd Oz (odz)) gene has been associated with a pair-rule phenotype. We identified and characterized new alleles of Drosophila Ten-m to establish that this gene is not responsible for segmentation defects but rather causes defects in motor neuron axon routing. In Ten-m mutants the inter-segmental nerve (ISN) often crosses segment boundaries and fasciculates with the ISN in the adjacent segment. Ten-m is expressed in the central nervous system and epidermal stripes during the stages when the growth cones of the neurons that form the ISN navigate to their targets. Over-expression of Ten-m in epidermal cells also leads to ISN misrouting. We also found that Filamin, an actin binding protein, physically interacts with the Ten-m protein. Mutations in cheerio, which encodes Filamin, cause defects in motor neuron axon routing like those of Ten-m. During embryonic development, the expression of Filamin and Ten-m partially overlap in ectodermal cells. These results suggest that Ten-m and Filamin in epidermal cells might together influence growth cone progression.

Cell type-dependent requirement for PIP box-regulated Cdt1 destruction during S phase

Previous studies have shown that Cdt1 overexpression in cultured cells can trigger re-replication, but not whether CRL4^Cdt2-triggered destruction of Cdt1 is required for normal mitotic cell cycle progression in vivo. We demonstrate that PIP box–mediated destruction of Cdt1^Dup during S phase is necessary for the cell division cycle in Drosophila.

DNA synthesis–coupled proteolysis of the prereplicative complex component Cdt1 by the CRL4^Cdt2 E3 ubiquitin ligase is thought to help prevent rereplication of the genome during S phase. To directly test whether CRL4^Cdt2-triggered destruction of Cdt1 is required for normal cell cycle progression in vivo, we expressed a mutant version of Drosophila Cdt1 (Dup), which lacks the PCNA-binding PIP box (Dup^ΔPIP) and which cannot be regulated by CRL4^Cdt2. Dup^ΔPIP is inappropriately stabilized during S phase and causes developmental defects when ectopically expressed. Dup^ΔPIP restores DNA synthesis to dup null mutant embryonic epidermal cells, but S phase is abnormal, and these cells do not progress into mitosis. In contrast, Dup^ΔPIP accumulation during S phase did not adversely affect progression through follicle cell endocycles in the ovary. In this tissue the combination of Dup^ΔPIP expression and a 50% reduction in Geminin gene dose resulted in egg chamber degeneration. We could not detect Dup hyperaccumulation using mutations in the CRL4^Cdt2 components Cul4 and Ddb1, likely because these cause pleiotropic effects that block cell proliferation. These data indicate that PIP box–mediated destruction of Dup is necessary for the cell division cycle and suggest that Geminin inhibition can restrain Dup^ΔPIP activity in some endocycling cell types.

The nuclear protein Waharan is required for endosomal-lysosomal trafficking in Drosophila

Here we report Drosophila Waharan (Wah), a 170-kD predominantly nuclear protein with two potential human homologues, as a newly identified regulator of endosomal trafficking. Wah is required for neuromuscular-junction development and muscle integrity. In muscles, knockdown of Wah caused novel accumulations of tightly packed electron-dense tubules, which we termed 'sausage bodies'. Our data suggest that sausage bodies coincide with sites at which ubiquitylated proteins and a number of endosomal and lysosomal markers co-accumulate. Furthermore, loss of Wah function generated loss of the acidic LysoTracker compartment. Together with data demonstrating that Wah acts earlier in the trafficking pathway than the Escrt-III component Drosophila Shrb (snf7 in Schizosaccharomyces pombe), our results indicate that Wah is essential for endocytic trafficking at the late endosome. Highly unexpected phenotypes result from Wah knockdown, in that the distribution of ubiquitylated cargos and endolysosomal morphologies are affected despite Wah being a predominant nuclear protein. This finding suggests the existence of a relationship between nuclear functions and endolysosomal trafficking. Future studies of Wah function will give us insights into this interesting phenomenon.

poly is required for nurse-cell chromosome dispersal and oocyte polarity in Drosophila

During Drosophila oogenesis, nurse cells undergo changes in chromosomal morphology, first from the polytenic form to a transient condensed phase known as the five-blob configuration, then into a diffuse polytenic-polyploid state for the remainder of oogenesis. The mechanism by which nurse-cell chromosome dispersal is regulated remains elusive. Mutations in several genes, including the heterogeneous ribonucleoprotein genes squid (sqd) and hrb27C, the alternative splicing factor gene poly U binding factor 68 kDa (pUf68, also known as half-pint), and the germ-line-specific gene ovarian tumor (otu), that produce defects in nurse-cell chromosome dispersal also produce defects in oocyte polarity, suggesting a link between these two processes. Here, we characterize a novel gene named poly, which, when mutated in the germ line, disrupts nurse-cell chromosome dispersal, as well as localization of anteroposterior and dorsoventral determinants in the oocyte. We also show that poly interacts genetically with hrb27C and otu. We conclude that poly is required for nurse-cell chromosome dispersal and oocyte polarization in the Drosophila germ-line. In addition, our interaction data suggest that poly is probably a member of the characterized mRNP complex that mediates both processes.

Neuropeptide biology in Drosophila

Drosophila melanogaster is since decades the most important invertebrate model. With the publishing of the genome sequence, Drosophila also became a pioneer in (neuro)peptide research. Neuropeptides represent a major group of signaling molecules that outnumber all other types of neurotransmitters/modulators and hormones. By means of bioinformatics 119 (neuro)peptide precursor genes have been predicted from the Drosophila genome. Using the neuropeptidomics technology 46 neuropeptides derived from 19 of these precursors could be biochemically characterized. At the cellular level, neuropeptides usually exert their action by binding to membrane receptors, many of which belong to the family of G-protein coupled receptors or GPCRs. Such receptors are the major target for many contemporary drugs. In this chapter, we will describe the identification, localization and functional characterization of neuropeptide-receptor pairs in Drosophila melanogaster.

Drosophila Larp associates with poly(A)-binding protein and is required for male fertility and syncytial embryo development

As the influence of mRNA translation upon cell cycle regulation becomes clearer, we searched for genes that might specify such control in Drosophila. A maternal-effect lethal screen identified mutants in the Drosophila gene for Larp (La-related protein) which displayed maternal-effect lethality and male sterility. A role for La protein has already been implicated in mRNA translation whereas Larp has been proposed to regulate mRNA stability. Here we demonstrate that Larp exists in a physical complex with, and also interacts genetically with, the translation regulator poly(A)-binding protein (PABP). Most mutant alleles of pAbp are embryonic lethal. However hypomorphic pAbp alleles show similar meiotic defects to larp mutants. We find that larp mutant-derived syncytial embryos show a range of mitotic phenotypes, including failure of centrosomes to migrate around the nuclear envelope, detachment of centrosomes from spindle poles, the formation of multipolar spindle arrays and cytokinetic defects. We discuss why the syncytial mitotic cycles and male meiosis should have a particularly sensitive requirement for Larp proteins in regulating not only transcript stability but also potentially the translation of mRNAs.

ISOGENIC AUTOSOMES TO BE APPLIED IN OPTIMAL SCREENING FOR NOVEL MUTANTS WITH VIABLE PHENOTYPES INDROSOPHILA MELANOGASTER

Most insertional mutagenesis screens of Drosophila performed to date have not used target chromosomes that have been checked for their suitability for phenotypic screens for viable phenotypes. To address this, we have generated a selection of stocks carrying either isogenized second chromosomes or isogenized third chromosomes, in a genetic background derived from a Canton-S wild-type strain. We have tested these stocks for a range of behavioral and other viable phenotypes. As expected, most lines are statistically indistinguishable from Canton-S in most phenotypes tested. The lines generated are now being used as target chromosomes in mutagenesis screens, and the characterization reported here will facilitate their use in screens of these lines for behavioral and other viable phenotypes.

Construction and characterization of deletions with defined end points in Drosophila using P elements in trans

We used P-element transposase-mediated "male recombination" between two P elements in trans to create genetic deletions that removed a number of loci, including the gene encoding the neuropeptide crustacean cardioactive peptide (CCAP). Two classes of recombinant chromosomes were produced. Approximately one-quarter were viable when homozygous or hemizygous, whereas the remaining lines caused homozygous and hemizygous lethality. Preliminary analyses using PCR and CCAP immunohistochemistry suggested that, whereas the DNA of the viable lines was largely intact, most lethal lines contained chromosomal deletions that were roughly bounded by the insertion sites of the two P elements used. Southern blot analyses of select lethal lines showed that the DNA flanking the deletion was indeed grossly intact whereas the intervening DNA could not be detected. Sequencing across the deletion in three of these lethal lines identified a single line bearing intact genomic DNA on either side of the deletion separated by 30 bp of P-element DNA. The method described here suggests a simple procedure for creating deletions with defined end points. Importantly, it can use preexisting P-element insertion strains and does not rely on the use of transposable elements that are engineered to cause specific DNA rearrangements.

Functional analysis of the SUMOylation pathway in Drosophila

SUMOylation, a reversible process used as a ‘fine-tuning’ mechanism to regulate the role of multiple proteins, is conserved throughout evolution. This post-translational modification affects several cellular processes by the modulation of subcellular localization, activity or stability of a variety of substrates. A growing number of proteins have been identified as targets for SUMOylation, although, for many of them, the role of SUMO conjugation on their function is unknown. The use of model systems might facilitate the study of SUMOylation implications in vivo. In the present paper, we have compiled what is known about SUMOylation in Drosophila melanogaster, where the use of genetics provides new insights on SUMOylation's biological roles.

The gene structure of the Drosophila melanogaster proto-oncogene, kayak, and its nested gene, fos-intronic gene

We present herein a new model for the structure of the Drosophila kayak gene as well as preliminary data on the functional differences of its various isoforms. kayak is a homolog of the human proto-oncogene, c-fos. kayak has three different starts of transcription, and therefore promoters (P)kay-alpha, (P)kay-beta and (P)kay-gamma. These three promoters lead to four different transcripts: kay-alpha, kay(sro), kay-beta and kay-gamma. (P)kay-alpha produces two different transcripts: kay-alpha and kay(sro) where the other two promoters, (P)kay-beta and (P)kay-gamma, produce a single transcript each. The transcripts kay-alpha, beta and gamma all splice into the mainbody of the kay gene, which codes for the DNA binding domain and leucine zipper; kay(sro) is not spliced. Also, within this region is a nested gene, fos-intronic gene (fig) which is transcribed in the opposite direction. fig codes for a predicted PP2C phosphatase. fig has two different promoters which produce two different transcripts, both in the same reading frame, fig-alpha and beta. This is an unusual gene structure for Drosophila. Only 13% of Drosophila genes have multiple promoters and only 7% have a nested gene. RT-PCR was performed on each transcript to determine the relative amounts of each RNA produced. All spliced kay transcripts appear to have equal abundance. The unspliced kay(sro) transcript has a lower abundance than kay-alpha. Both fig transcripts are also detected in all stages tested. Lethal phase analysis and complementation testing suggest that the three isoforms of kayak may have different functions.

COPI vesicle transport is a common requirement for tube expansion in Drosophila

BACKGROUND

Tube expansion defects like stenoses and atresias cause devastating human diseases. Luminal expansion during organogenesis begins to be elucidated in several systems but we still lack a mechanistic view of the process in many organs. The Drosophila tracheal respiratory system provides an amenable model to study tube size regulation. In the trachea, COPII anterograde transport of luminal proteins is required for extracellular matrix assembly and the concurrent tube expansion.

PRINCIPAL FINDINGS

We identified and analyzed Drosophila COPI retrograde transport mutants with narrow tracheal tubes. gammaCOP mutants fail to efficiently secrete luminal components and assemble the luminal chitinous matrix during tracheal tube expansion. Likewise, tube extension is defective in salivary glands, where it also coincides with a failure in the luminal deposition and assembly of a distinct, transient intraluminal matrix. Drosophila gammaCOP colocalizes with cis-Golgi markers and in gammaCOP mutant embryos the ER and Golgi structures are severely disrupted. Analysis of gammaCOP and Sar1 double mutants suggests that bidirectional ER-Golgi traffic maintains the ER and Golgi compartments and is required for secretion and assembly of luminal matrixes during tube expansion.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate the function of COPI components in organ morphogenesis and highlight the common role of apical secretion and assembly of transient organotypic matrices in tube expansion. Intraluminal matrices have been detected in the notochord of ascidians and zebrafish COPI mutants show defects in notochord expansion. Thus, the programmed deposition and growth of distinct luminal molds may provide distending forces during tube expansion in diverse organs.

A Drosophila orthologue of larp protein family is required for multiple processes in male meiosis

It is important for the proper execution of cell division in both mitosis and meiosis that the chromosome segregation, cytokinesis, and partition of cell organelles progress in smooth coordination. We show here that the mitochondria inheritance is closely linked with microtubules during meiotic divisions in Drosophila males. They are first clustered in a cell equator at metaphase associated with astral microtubules and then distributed along central spindle microtubules after anaphase. The molecular mechanism for the microtubule-dependent inheritance of mitochondria in male meiosis has not been demonstrated yet. We first isolated mutations for a larp gene that is highly conserved among eukaryotes and showed that these mutant males exhibited multiple meiotic phenotypes such as a failure of chromosome segregation, cytokinesis, and mitochondrial partition. Our cytological examination revealed that the mutants showed defects in spindle pole organization and spindle formation. The larp encodes a Drosophila orthologue of a La-related protein containing a domain exhibiting an outstanding homology with a La type RNA-binding protein. Surprisingly, the dLarp protein is localized in the cytoplasm of the male germ line cells, as observed by its distinct co-localization with mitochondria in early spermatocytes and during meiotic divisions. We discuss here the essential role that dLarp plays in multiple processes in Drosophila male meiosis.

A key role of Pox meso in somatic myogenesis of Drosophila

The Pax gene Pox meso (Poxm) was the first and so far only gene whose initial expression was shown to occur specifically in the anlage of the somatic mesoderm, yet its role in somatic myogenesis remained unknown. Here we show that it is one of the crucial genes regulating the development of the larval body wall muscles in Drosophila. It has two distinct functions expressed during different phases of myogenesis. The early function, partially redundant with the function of lethal of scute [l(1)sc], demarcates the ;Poxm competence domain', a domain of competence for ventral and lateral muscle development and for the determination of at least some adult muscle precursor cells. The late function is a muscle identity function, required for the specification of muscles DT1, VA1, VA2 and VA3. Our results led us to reinterpret the roles of l(1)sc and twist in myogenesis and to propose a solution of the 'l(1)sc conundrum'.

Presynaptic establishment of the synaptic cleft extracellular matrix is required for post-synaptic differentiation

Formation and regulation of excitatory glutamatergic synapses is essential for shaping neural circuits throughout development. In a Drosophila genetic screen for synaptogenesis mutants, we identified mind the gap (mtg), which encodes a secreted, extracellular N-glycosaminoglycan-binding protein. MTG is expressed neuronally and detected in the synaptic cleft, and is required to form the specialized transsynaptic matrix that links the presynaptic active zone with the post-synaptic glutamate receptor (GluR) domain. Null mtg embryonic mutant synapses exhibit greatly reduced GluR function, and a corresponding loss of localized GluR domains. All known post-synaptic signaling/scaffold proteins functioning upstream of GluR localization are also grossly reduced or mislocalized in mtg mutants, including the dPix-dPak-Dock cascade and the Dlg/PSD-95 scaffold. Ubiquitous or neuronally targeted mtg RNA interference (RNAi) similarly reduce post-synaptic assembly, whereas post-synaptically targeted RNAi has no effect, indicating that presynaptic MTG induces and maintains the post-synaptic pathways driving GluR domain formation. These findings suggest that MTG is secreted from the presynaptic terminal to shape the extracellular synaptic cleft domain, and that the cleft domain functions to mediate transsynaptic signals required for post-synaptic development.

Mitch a rapidly evolving component of the Ndc80 kinetochore complex required for correct chromosome segregation in Drosophila

We identified an essential kinetochore protein, Mitch, from a genetic screen in D. melanogaster. Mitch localizes to the kinetochore, and its targeting is independent of microtubules (MTs) and several other known kinetochore components. Animals carrying mutations in mitch die as late third-instar larvae; mitotic neuroblasts in larval brains exhibit high levels of aneuploidy. Analysis of fixed D. melanogaster brains and mitch RNAi in cultured cells, as well as video recordings of cultured mitch mutant neuroblasts, reveal that chromosome alignment in mitch mutants is compromised during spindle formation, with many chromosomes displaying persistent mono-orientation. These misalignments lead to aneuploidy during anaphase. Mutations in mitch also disrupt chromosome behavior during both meiotic divisions in spermatocytes: the entire chromosome complement often moves to only one spindle pole. Mutant mitotic cells exhibit contradictory behavior with respect to the spindle assembly checkpoint (SAC). Anaphase onset is delayed in untreated cells, probably because incorrect kinetochore attachment maintains the SAC. However, mutant brain cells and mitch RNAi cells treated with MT poisons prematurely disjoin their chromatids, and exit mitosis. These data suggest that Mitch participates in SAC signaling that responds specifically to disruptions in spindle microtubule dynamics. The mitch gene corresponds to the transcriptional unit CG7242, and encodes a protein that is a possible ortholog of the Spc24 or Spc25 subunit of the Ndc80 kinetochore complex. Despite the crucial role of Mitch in cell division, the mitch gene has evolved very rapidly among species in the genus Drosophila.

D1 dopamine receptor dDA1 is required in the mushroom body neurons for aversive and appetitive learning in Drosophila

Drosophila has robust behavioral plasticity to avoid or prefer the odor that predicts punishment or food reward, respectively. Both types of plasticity are mediated by the mushroom body (MB) neurons in the brain, in which various signaling molecules play crucial roles. However, important yet unresolved molecules are the receptors that initiate aversive or appetitive learning cascades in the MB. We have shown previously that D1 dopamine receptor dDA1 is highly enriched in the MB neuropil. Here, we demonstrate that dDA1 is a key receptor that mediates both aversive and appetitive learning in pavlovian olfactory conditioning. We identified two mutants, dumb1 and dumb2, with abnormal dDA1 expression. When trained with the same conditioned stimuli, both dumb alleles showed negligible learning in electric shock-mediated conditioning while they exhibited moderately impaired learning in sugar-mediated conditioning. These phenotypes were not attributable to anomalous sensory modalities of dumb mutants because their olfactory acuity, shock reactivity, and sugar preference were comparable to those of control lines. Remarkably, the dumb mutant's impaired performance in both paradigms was fully rescued by reinstating dDA1 expression in the same subset of MB neurons, indicating the critical roles of the MB dDA1 in aversive as well as appetitive learning. Previous studies using dopamine receptor antagonists implicate the involvement of D1/D5 receptors in various pavlovian conditioning tasks in mammals; however, these have not been supported by the studies of D1- or D5-deficient animals. The findings described here unambiguously clarify the critical roles of D1 dopamine receptor in aversive and appetitive pavlovian conditioning.

Transcriptional regulation of the Drosophila rfc1 gene by the DRE-DREF pathway

The DNA replication-related element (DRE) is a common 8-bp sequence (5'-TATCGATA) found in the promoters of many DNA replication-related genes, to which DRE-binding factor (DREF) specifically binds to activate transcription. Replication factor C (RFC) is an essential five-subunit complex in DNA replication, the largest subunit being RFC140. We first identified the gene (rfc1) encoding the Drosophila RFC140 (dRFC140) protein and then isolated a mutant. The phenotypes suggested that the gene is essential for cell-cycle progression, and immunocytochemical studies also indicated a relation between its expression and the cell cycle. The rfc1 gene contains three DRE-like sequences in its 5'-flanking region, one of them perfectly matching DRE and the other two demonstrating a match in seven of eight nucleotides. These sequences were named DRE1 (-63 to -69), DRE2 (-378 to -385), and DRE3 (-1127 to -1134), respectively. Immunostaining of polytene chromosomes in third-instar larvae using anti-DREF sera detected a specific band in 82E2 of 3R chromosome, containing the rfc1 gene region. Band-mobility shift assays using Drosophila Kc cell nuclear extracts revealed that DREF binds to DRE1, -2, and -3 in vitro, and chromatin immunoprecipitation using anti-DREF IgG confirmed that this occurs in vivo. Luciferase transient expression assays in S2 cells further suggested that DREs in the rfc1 promoter are involved in transcriptional regulation of the gene. Moreover, rfc1 promoter activity was reduced by 38% in DREF double-stranded RNA-treated S2 cells. These results indicate that DREF positively regulates the rfc1 promoter.

The Drosophila p21 activated kinase Mbt regulates the actin cytoskeleton and adherens junctions to control photoreceptor cell morphogenesis

The p21 activated kinase (Pak) family of protein kinases are involved in many cellular functions like re-organisation of the cytoskeleton, transcriptional control, cell division, and survival. These pleiotropic actions are reflected in a plethora of known interacting proteins and phosphorylation substrates. Yet, the integration of a single Pak protein into signalling pathways controlling a particular developmental process are less well studied. For two of the three known Pak proteins in Drosophila melanogaster, D-Pak and Mbt, distinct functions during eye development have been established. In this study we undertook a genetic approach to identify proteins acting in the Mbt signalling pathway during photoreceptor cell morphogenesis. The genetic screen identified the actin depolymerisation factor Twinstar/Cofilin as one target of Mbt signalling. Twinstar/Cofilin becomes phosphorylated upon activation of Mbt. However, biochemical and genetic experiments question the role of the LIM domain protein kinase (Limk) as a major link between Mbt and Twinstar/Cofilin as it has been suggested for other PAK proteins. Constitutive activation of Mbt not only disturbs the actin cytoskeleton but also affects adherens junction organisation indicating a requirement of the protein in cell adhesion dependent processes during photoreceptor cell differentiation.

Drosophila mus301/spindle-C encodes a helicase with an essential role in double-strand DNA break repair and meiotic progression

mus301 was identified independently in two genetic screens, one for mutants hypersensitive to chemical mutagens and another for maternal mutants with eggshell defects. mus301 is required for the proper specification of the oocyte and for progression through meiosis in the Drosophila ovary. We have cloned mus301 and show that it is a member of the Mus308 subfamily of ATP-dependent helicases and the closest homolog of human and mouse HEL308. Functional analyses demonstrate that Mus301 is involved in chromosome segregation in meiosis and in the repair of double-strand-DNA breaks in both meiotic and mitotic cells. Most of the oogenesis defects of mus301 mutants are suppressed by mutants in the checkpoint kinase Mei41 and in MeiW68, the Spo11 homolog that is thought to generate the dsDNA breaks that initiate recombination, indicating that these phenotypes are caused by activation of the DNA damage checkpoint in response to unrepaired Mei-W68-induced dsDNA breaks. However, neither mei-W68 nor mei-41 rescue the defects in oocyte specification of mus301 mutants, suggesting that this helicase has another function in oocyte selection that is independent from its role in meiotic recombination.

TheDrosophilaphosphatidylinositol transfer protein encoded byvibratoris essential to maintain cleavage-furrow ingression in cytokinesis

Cytokinesis requires the coordination of cytoskeletal and plasma membrane dynamics. A role for phosphatidylinositol lipids has been proposed for the successful completion of cytokinesis but this is still poorly characterised. Here, we show mutants of the gene vibrator, previously found to encode the Drosophila phosphatidylinositol transfer protein, produce multinucleate cells indicative of cytokinesis failure in male meiosis. Examination of fixed preparations of mutant spermatocytes showed contractile rings of anillin and actin that were of normal appearance at early stages but were larger and less well organised at later stages of cytokinesis than in wild-type cells. Time-lapse imaging revealed sequential defects in cytokinesis of vibrator spermatocytes. In cells that fail cytokinesis, central spindle formation occurred correctly, but furrow ingression was delayed and the central spindle did not become compressed to the extent seen in wild-type cells. Cells then stalled at this point before the apparent connection between the constricted cytoskeleton and the plasma membrane was lost; the furrow then underwent elastic regression. We discuss these defects in relation to multiple functions of phosphoinositol lipids in regulating actin dynamics and membrane synthesis.

Distinct functions of the leucine-rich repeat transmembrane proteins capricious and tartan in the Drosophila tracheal morphogenesis

A key step in organogenesis of the Drosophila tracheal system is the integration of isolated tracheal metameres into a connected tubular network. The interaction of tracheal cells with surrounding mesodermal cells is crucial in this process. In particular, single mesodermal cells called bridge-cells are essential for the guided outgrowth of dorsal trunk branches to direct formation of the main airway, the dorsal trunk. Here, we present evidence that the two leucine-rich repeat transmembrane proteins Capricious and Tartan contribute differently to the formation of branch interconnections during tracheal development. Capricious is specifically localized on the surface of bridge-cells and facilitates the outgrowing dorsal trunk cells of adjacent metameres toward each other. We show that Capricious requires both extracellular and intracellular domains during tracheal branch outgrowth. In contrast, Tartan is expressed broadly in mesodermal cells and exerts its role in tracheal branch outgrowth through its extracellular domain. We propose that Capricious contributes to the instructive role of bridge-cells whereas Tartan provides permissive substrate for the migrating tracheal cells during the network formation.

Glorund, a Drosophila hnRNP F/H homolog, is an ovarian repressor of nanos translation

Patterning of the anterior-posterior body axis of the Drosophila embryo requires production of Nanos protein selectively in the posterior. Spatially restricted Nanos synthesis is accomplished by translational repression of unlocalized nanos mRNA together with translational activation of posteriorly localized nanos. Repression of unlocalized nanos mRNA is mediated by a bipartite translational control element (TCE) in its 3' untranslated region. TCE stem-loop II functions during embryogenesis, through its interaction with the Smaug repressor. Stem-loop III represses unlocalized nanos mRNA during oogenesis, but trans-acting factors that carry out this function have remained elusive. Here we identify a Drosophila hnRNP, Glorund, that interacts specifically with stem-loop III. We establish that the ability of the TCE to repress translation in vivo reflects its ability to bind Glorund in vitro. These data, together with the analysis of a glorund null mutant, reveal a specific role for an hnRNP in repression of nanos translation during oogenesis.

spn-F encodes a novel protein that affects oocyte patterning and bristle morphology in Drosophila

The anteroposterior and dorsoventral axes of the Drosophila embryo are established during oogenesis through the activities of Gurken (Grk), a Tgfalpha-like protein, and the Epidermal growth factor receptor (Egfr). spn-F mutant females produce ventralized eggs similar to the phenotype produced by mutations in the grk-Egfr pathway. We found that the ventralization of the eggshell in spn-F mutants is due to defects in the localization and translation of grk mRNA during mid-oogenesis. Analysis of the microtubule network revealed defects in the organization of the microtubules around the oocyte nucleus. In addition, spn-F mutants have defective bristles. We cloned spn-F and found that it encodes a novel coiled-coil protein that localizes to the minus end of microtubules in the oocyte, and this localization requires the microtubule network and a Dynein heavy chain gene. We also show that Spn-F interacts directly with the Dynein light chain Ddlc-1. Our results show that we have identified a novel protein that affects oocyte axis determination and the organization of microtubules during Drosophila oogenesis.

emc has a role in dorsal appendage fate formation in Drosophila oogenesis

extramacrochaetae (emc) functions during many developmental processes in Drosophila, such as sensory organ formation, sex determination, wing vein differentiation, regulation of eye photoreceptor differentiation, cell proliferation and development of the Malpighian tubules, trachea and muscles in the embryo. It encodes a Helix-Loop-Helix transcription factor that negatively regulates bHLH proteins. We show here that emc mRNA and protein are present throughout oogenesis in a dynamic expression pattern and that emc is involved in the regulation of chorionic appendage formation during late oogenesis. Expression of sense and antisense emc constructs as well as emc follicle cell clones leads to eggs with shorter, thicker dorsal appendages that are closer together at base than in the wild type. We demonstrate that emc lies downstream of fs(1)K10, gurken and EGFR in the Grk/EGFR signalling pathway and that it participates in controlling Broad-Complex expression at late stages of oogenesis.

A Drosophila model of multiple endocrine neoplasia type 2

Dominant mutations in the Ret receptor tyrosine kinase lead to the familial cancer syndrome multiple endocrine neoplasia type 2 (MEN2). Mammalian tissue culture studies suggest that RetMEN2 mutations significantly alter Ret-signaling properties, but the precise mechanisms by which RetMEN2 promotes tumorigenesis remain poorly understood. To determine the signal transduction pathways required for RetMEN2 activity, we analyzed analogous mutations in the Drosophila Ret ortholog dRet. Overexpressed dRetMEN2 isoforms targeted to the developing retina led to aberrant cell proliferation, inappropriate cell fate specification, and excessive Ras pathway activation. Genetic analysis indicated that dRetMEN2 acts through the Ras-ERK, Src, and Jun kinase pathways. A genetic screen for mutations that dominantly suppress or enhance dRetMEN2 phenotypes identified new genes that are required for the phenotypic outcomes of dRetMEN2 activity. Finally, we identified human orthologs for many of these genes and examined their status in human tumors. Two of these loci showed loss of heterozygosity (LOH) within both sporadic and MEN2-associated pheochromocytomas, suggesting that they may contribute to Ret-dependent oncogenesis.

Drosophila Klp67A is required for proper chromosome congression and segregation during meiosis I

Drosophila Klp67A belongs to the Kip3 subfamily of Kinesin-type microtubule catastrophe factors. In primary spermatocytes, loss of klp67A leads to defects in karyokinesis and cytokinesis. We show that these cells formed disorganised, bipolar spindles that contained increased numbers of microtubules. The kinetochore fibres were wavy and bent, whereas astral microtubules appeared abnormally robust and formed cortical bundles. Time-lapse studies revealed that during biorientation, the chromosomes in klp67A mutant cells continued to reorient for about twice as long as those in control cells. Metaphase plates were poorly defined in the mutants and often formed at non-equatorial positions. Consistent with the above abnormalities in chromosome congression, we found that in wild-type cells Klp67A associated with prometaphase/metaphase kinetochores before redistributing to the central spindle at anaphase onset. Although the timing of this redistribution of kinetochores argues against a role in anaphase chromosome segregation, dyads in the mutants disjoined but exhibited greatly diminished poleward velocities. They travelled on average at approximately 34% of the velocity of their wild-type counterparts and often decondensed at non-polar locations. Hypomorphic mutations of klp67A may lead to segregation defects.

The Kavar D dominant female-sterile mutations of Drosophila reveal a role for the maternally provided α-tubulin4 isoform in cleavage spindle maintenance and elongation

The dominant-negative female-sterile Kavar(D) mutations and their revertant kavar(r) alleles identify the alphaTubulin67C gene of Drosophila melanogaster, which codes for the maternally provided alpha-tubulin(4) isoform. The mutations result in the formation of monopolar, collapsed spindles (each with two nearby centrosomes, a tassel of microtubules and overcondensed chromosomes), thus revealing a novel function for alpha-tubulin(4) in spindle maintenance and elongation. Molecular features of the two Kavar(D) alleles and a kavar(null) allele are described and models for their actions are discussed.

Drosophila p24 homologues eclair and baiser are necessary for the activity of the maternally expressed Tkv receptor during early embryogenesis

p24 proteins are assumed to play an important role in the transport of secreted and transmembrane proteins into membranes. However, only few cargo proteins are known that partially, but in no case completely require p24 proteins for membrane transport. Here, we show that two p24 proteins are essential for dorsoventral patterning of Drosophila melanogaster embryo. Mutations in the genes, eclair (eca) and baiser (bai), encoding two p24 proteins reduce signalling by the TGF-beta homologue, Dpp, in early embryos. This effect is strictly maternal and specific to early embryogenesis, as Dpp signalling in other contexts is not notably affected. We provide genetic evidence that in the absence of eca or bai function in the oocyte, the maternally expressed type I TGF-beta receptor Tkv is not active. We propose that during early embryogenesis eca and bai are specifically required for the activity of the maternal Tkv, while the zygotic Tkv is not affected in the mutant embryos. Mutations in either eca or bai are sufficient for the depletion of Tkv activity and no enhancement of the phenotypes was observed in embryos derived from oocytes mutant for both genes. The dependence of maternal Tkv protein on the products of p24 genes may serve as an in vivo model for studying p24 proteins.

The BDGP gene disruption project: single transposon insertions associated with 40% of Drosophila genes

The Berkeley Drosophila Genome Project (BDGP) strives to disrupt each Drosophila gene by the insertion of a single transposable element. As part of this effort, transposons in >30,000 fly strains were localized and analyzed relative to predicted Drosophila gene structures. Approximately 6300 lines that maximize genomic coverage were selected to be sent to the Bloomington Stock Center for public distribution, bringing the size of the BDGP gene disruption collection to 7140 lines. It now includes individual lines predicted to disrupt 5362 of the 13,666 currently annotated Drosophila genes (39%). Other lines contain an insertion at least 2 kb from others in the collection and likely mutate additional incompletely annotated or uncharacterized genes and chromosomal regulatory elements. The remaining strains contain insertions likely to disrupt alternative gene promoters or to allow gene misexpression. The expanded BDGP gene disruption collection provides a public resource that will facilitate the application of Drosophila genetics to diverse biological problems. Finally, the project reveals new insight into how transposons interact with a eukaryotic genome and helps define optimal strategies for using insertional mutagenesis as a genomic tool.

Research resources for Drosophila: the expanding universe

Drosophila melanogaster has been the subject of research into central questions about biological mechanisms for almost a century. The experimental tools and resources that are available or under development for D. melanogaster and its related species, particularly those for genomic analysis, are truly outstanding. Here we review three types of resource that have been developed for D. melanogaster research: databases and other sources of information, biological materials and experimental services. These resources are there to be exploited and we hope that this guide will encourage new uses for D. melanogaster information, materials and services, both by those new to flies and by experienced D. melanogaster researchers.

parva germina, A gene involved in germ cell maintenance during male and female Drosophila gametogenesis

We report the initial characterization of a gene, parva germina (pag), required for germ cell maintenance in both males and females. pag gonads contain a small number of germline stem cells at the onset of gametogenesis. In contrast, adult mutant gonads are either empty or have a very small number of germ cells that never develop in 16-cell cysts. Ovarioles and testes, therefore, are rudimentary, and the very few germ cells they contain are unable to differentiate into eggs or sperm. Germline stem cells are progressively depleted over time. The average number of germ cells, therefore, decreases in pag mutant ovarioles with the age of the mother, whereas the proportion of agametic germaria goes up. These observations suggest that the pag gene product is involved in germ cell maintenance in both male and female gametogenesis.