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Summary Cell competition is a homeostatic process in which proliferating cells compete for survival. Elimination of otherwise normal healthy cells through competition is important during development and has recently been shown to contribute to maintaining tissue health during organismal aging. The mechanisms that allow for ongoing cell competition during adult life could, in principle, contribute to tumorigenesis. However, direct evidence supporting this hypothesis has been lacking. Here, we provide evidence that cell competition drives tumor formation in a Drosophila model of epithelial cancer. Cells expressing EGFR together with the conserved microRNA miR-8 acquire the properties of supercompetitors. Neoplastic transformation and metastasis depend on the ability of these cells to induce apoptosis and engulf nearby cells. miR-8 expression causes genome instability by downregulating expression of the Septin family protein Peanut. Cytokinesis failure due to downregulation of Peanut is required for tumorigenesis. This study provides evidence that the cellular mechanisms that drive cell competition during normal tissue growth can be co-opted to drive tumor formation and metastasis. Analogous mechanisms for cytokinesis failure may lead to polyploid intermediates in tumorigenesis in mammalian cancer models. [ABSTRACT FROM AUTHOR]

Summary: The Hippo signaling pathway acts upon the Yorkie transcriptional activator to control tissue growth in Drosophila. Activated Yorkie drives growth by stimulating cell proliferation and inhibiting apoptosis, but how it achieves this is not understood. Yorkie is known to activate Cyclin E (CycE) and the apoptosis inhibitor DIAP1. However, overexpression of these targets is not sufficient to cause tissue overgrowth. Here we show that Yorkie also activates expression of the bantam microRNA, a known regulator of both proliferation and apoptosis. bantam overexpression mimics Yorkie activation while loss of bantam function slows the rate of cell proliferation. bantam is necessary for Yorkie-induced overproliferation and bantam overexpression is sufficient to rescue survival and proliferation of yorkie mutant cells. Finally, we show that bantam levels are regulated during both developmentally programmed proliferation arrest and apoptosis. In summary, the results show that the Hippo pathway regulates expression of bantam to control tissue growth in Drosophila. [Copyright &y& Elsevier]

Examines Decapentaplegic gradient formation in the Drosophila wing imaginal disc. Factors affecting the size of adult organisms; Properties of the Decapentaplegic morphogen gradient; Role of Decapentaplegic-green fluorescent protein in wing development; Formation of an extracellular gradient by Decapentaplegic-green fluorescent protein.

Reports that spatially localized expression of the homeobox gene apterous (ap) specifies the identity of dorsal cells in the wing of Drosophila. Boundary of ap expression and the dorsal-ventral compartment boundary in the wing; Need for ap to specify dorsal wing identity in the wing; Specification of wing margin.

Summary: Though usually thought of as mediating communication between adjacent cells, Notch–Delta signaling can take place over a longer range through cellular processes known as ‘filopodia’. A recent study shows how the dynamics of filopodia can confer robustness to Notch–Delta dependent patterning. [ABSTRACT FROM AUTHOR]

Background Cancers develop in a complex mutational landscape. Interaction of genetically abnormal cancer cells with normal stromal cells can modify the local microenvironment to promote disease progression for some tumor types. Genetic models of tumorigenesis provide the opportunity to explore how combinations of cancer driver mutations confer distinct properties on tumors. Previous Drosophila models of EGFR-driven cancer have focused on epithelial neoplasia. Results Here, we report a Drosophila genetic model of EGFR-driven tumorigenesis in which the neoplastic transformation depends on interaction between epithelial and mesenchymal cells. We provide evidence that the secreted proteoglycan Perlecan can act as a context-dependent oncogene cooperating with EGFR to promote tumorigenesis. Coexpression of Perlecan in the EGFR-expressing epithelial cells potentiates endogenous Wg/Wnt and Dpp/BMP signals from the epithelial cells to support expansion of a mesenchymal compartment. Wg activity is required in the epithelial compartment, whereas Dpp activity is required in the mesenchymal compartment. This genetically normal mesenchymal compartment is required to support growth and neoplastic transformation of the genetically modified epithelial population. Conclusions We report a genetic model of tumor formation that depends on crosstalk between a genetically modified epithelial cell population and normal host mesenchymal cells. Tumorigenesis in this model co-opts a regulatory mechanism that is normally involved in controlling growth of the imaginal disc during development. [ABSTRACT FROM AUTHOR]

Summary: Background: The epidermal growth factor receptor (EGFR) and Hippo signaling pathways control cell proliferation and apoptosis to promote tissue growth during development. Misregulation of these pathways is implicated in cancer. Our understanding of the mechanisms that integrate the activity of these pathways remains fragmentary. This study identifies bantam microRNA as a common target of these pathways and suggests a mechanistic link between them. Results: The EGFR pathway acts through bantam to control tissue growth. bantam expression is regulated by the EGFR pathway, acting via repression of the transcriptional repressor Capicua. Thus EGFR signaling induces bantam expression by alleviating the effects of a repressor. bantam in turn acts in a negative feedback loop to limit Capicua expression. Conclusions: bantam appears to be a transcriptional target of both the EGFR and Hippo growth control pathways. Feedback regulation by bantam on Capicua provides a means to link signal propagation by the EGFR pathway to activity of the Hippo pathway and may play an important role in integration of these two pathways in growth control. [ABSTRACT FROM AUTHOR]

Examines evidence on the formation of morphogen gradients in tissues. Role of endocytosis and resecretion in ligand transport; Importance of ligand turnover in gradient formation; Function of cytoplasmic projections in morphogen transport; Limitation of ligand movement through the extracellular space.

Summary: During oogenesis, female animals load their eggs with messenger RNAs (mRNAs) that will be translated to produce new proteins in the developing embryo. Some of these maternally provided mRNAs are stable and continue to contribute to development long after the onset of transcription of the embryonic (zygotic) genome. However, a subset of maternal mRNAs are degraded during the transition from purely maternal to mixed maternal-zygotic gene expression. In Drosophila, two independent RNA degradation pathways are used to promote turnover of maternal transcripts during the maternal-to-zygotic transition . The first is driven by maternally encoded factors, including SMAUG , whereas the second is activated about 2 hr after fertilization, coinciding with the onset of zygotic transcription. Here, we report that a cluster of zygotically expressed microRNAs (miRNAs) targets maternal mRNAs for turnover, as part of the zygotic degradation pathway. miRNAs are small noncoding RNAs that silence gene expression by repressing translation of their target mRNAs and by promoting mRNA turnover. Intriguingly, use of miRNAs to promote mRNA turnover during the maternal-to-zygotic transition appears to be a conserved phenomenon because a comparable role was reported for miR-430 in zebrafish . The finding that unrelated miRNAs regulate the maternal to zygotic transition in different animals suggests convergent evolution. [Copyright &y& Elsevier]

Summary: microRNAs (miRNAs) bind to specific messenger RNA targets to posttranscriptionally modulate their expression. Understanding the regulatory relationships between miRNAs and targets remains a major challenge. Many miRNAs reduce expression of their targets to inconsequential levels. It has also been proposed that miRNAs might adjust target expression to an optimal level. Here we analyze the consequences of mutating the conserved miRNA miR-8 in Drosophila. We identify atrophin as a direct target of miR-8. miR-8 mutant phenotypes are attributable to elevated atrophin activity, resulting in elevated apoptosis in the brain and in behavioral defects. Reduction of atrophin levels in miR-8-expressing cells to below the level generated by miR-8 regulation is detrimental, providing evidence for a “tuning target” relationship between them. Drosophila atrophin is related to the atrophin family of mammalian transcriptional regulators, implicated in the neurodegenerative disorder DRPLA. The regulatory relationship between miR-8 and atrophin orthologs is conserved in mammals. [Copyright &y& Elsevier]

Summary: MicroRNAs are small noncoding RNAs that serve as posttranscriptional regulators of gene expression in higher eukaryotes. Their widespread and important role in animals is highlighted by recent estimates that 20%–30% of all genes are microRNA targets. Here, we report that a large set of genes involved in basic cellular processes avoid microRNA regulation due to short 3′UTRs that are specifically depleted of microRNA binding sites. For individual microRNAs, we find that coexpressed genes avoid microRNA sites, whereas target genes and microRNAs are preferentially expressed in neighboring tissues. This mutually exclusive expression argues that microRNAs confer accuracy to developmental gene-expression programs, thus ensuring tissue identity and supporting cell-lineage decisions. [Copyright &y& Elsevier]

Cell proliferation, cell death, and pattern formation are coordinated in animal development. Although many proteins that control cell proliferation and apoptosis have been identified, the means by which these effectors are linked to the patterning machinery remain poorly understood. Here, we report that the bantam gene of Drosophila encodes a 21 nucleotide microRNA that promotes tissue growth. bantam expression is temporally and spatially regulated in response to patterning cues. bantam microRNA simultaneously stimulates cell proliferation and prevents apoptosis. We identify the pro-apoptotic gene hid as a target for regulation by bantam miRNA, providing an explanation for bantam''s anti-apoptotic activity. [Copyright &y& Elsevier]

Studies the role of transmembrane leucine-rich proteins, capricious and tartan, during dorsal-ventral boundary formation in the Drosophila wing. Sources of signaling proteins; Segregation of cells at compartment boundaries; Differential expression of cell adhesion molecules.

Summary Cancers develop in a complex mutational landscape. Genetic models of tumor formation have been used to explore how combinations of mutations cooperate to promote tumor formation in vivo. Here, we identify lactate dehydrogenase (LDH), a key enzyme in Warburg effect metabolism, as a cooperating factor that is both necessary and sufficient for epidermal growth factor receptor (EGFR)-driven epithelial neoplasia and metastasis in a Drosophila model. LDH is upregulated during the transition from hyperplasia to neoplasia, and neoplasia is prevented by LDH depletion. Elevated LDH is sufficient to drive this transition. Notably, genetic alterations that increase glucose flux, or a high-sugar diet, are also sufficient to promote EGFR-driven neoplasia, and this depends on LDH activity. We provide evidence that increased LDHA expression promotes a transformed phenotype in a human primary breast cell culture model. Furthermore, analysis of publically available cancer data showed evidence of synergy between elevated EGFR and LDHA activity linked to poor clinical outcome in a number of human cancers. Altered metabolism has generally been assumed to be an enabling feature that accelerates cancer cell proliferation. Our findings provide evidence that sugar metabolism may have a more profound role in driving neoplasia than previously appreciated. Highlights • LDH upregulation is required for the transition from hyperplasia to neoplasia • LDH expression drives tumor formation in the context of EGFR overexpression • Increased sugar uptake drives tumor formation in the Drosophila EGFR model • Synergy between EGFR and LDHA correlates with poor outcome in human cancer Eichenlaub et al. examine gene expression changes during the transition from hyperplasia to neoplasia and identify lactate dehydrogenase as a key driver of neoplasia in a Drosophila EGFR model. Elevated sugar flux or a high-sugar diet also drive neoplasia. Synergy between EGFR and LDHA correlates with poor clinical outcome in some human cancers. [ABSTRACT FROM AUTHOR]

MicroRNAs are abundant in animal genomes, yet little is known about their functions in vivo. Here, we report the production of 80 new Drosophila miRNA mutants by targeted homologous recombination. These mutants remove 104 miRNAs. Together with 15 previously reported mutants, this collection includes 95 mutants deleting 130 miRNAs. Collectively, these genes produce over 99% of all Drosophila miRNAs, measured by miRNA sequence reads. We present a survey of developmental and adult miRNA phenotypes. Over 80% of the mutants showed at least one phenotype using a p < 0.01 significance threshold. We observed a significant correlation between miRNA abundance and phenotypes related to survival and lifespan, but not to most other phenotypes. miRNA cluster mutants were no more likely than single miRNA mutants to produce significant phenotypes. This mutant collection will provide a resource for future analysis of the biological roles of Drosophila miRNAs., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Primary human cells can be transformed into tumor cells by a defined set of genetic alterations including telomerase, oncogenic Ras(V12), and the tumor suppressors p53 and pRb. SV40 small T (ST) is required for anchorage-independent growth in vitro and in vivo. Here, we identify the Hippo tumor suppressor pathway as a critical target of ST in cellular transformation. We report that ST uncouples YAP from the inhibitory activity of the Hippo pathway through PAK1-mediated inactivation of NF2. Membrane-tethered activated PAK is sufficient to bypass the requirement for ST in anchorage-independent growth. PAK acts via YAP to mediate the transforming effects of ST. Activation of endogenous YAP is required for ST-mediated transformation and is sufficient to bypass ST in anchorage-independent growth and xenograft tumor formation. Our findings uncover the Hippo tumor suppressor pathway as a final gatekeeper to transformation and tumorigenesis of primary cells., (Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.)

We sequenced Drosophila head RNA to identify a small set of miRNAs that undergo robust circadian cycling. We concentrated on a cluster of six miRNAs, mir-959-964, all of which peak at about ZT12 or lights off. The cluster pri-miRNA is transcribed under bona fide circadian transcriptional control, and all six mature miRNAs have short half-lives, a requirement for cycling. A viable Gal4 knockin strain localizes prominent cluster miRNA expression to the adult head fat body. Analysis of cluster knockout and overexpression strains indicates that innate immunity, metabolism, and feeding behavior are under cluster miRNA regulation. Manipulation of food intake also affects the levels and timing of cluster miRNA transcription with no more than minor effects on the core circadian oscillator. These observations indicate a feedback circuit between feeding time and cluster miRNA expression function as well as a surprising role of posttranscriptional regulation in the circadian control of these phenotypes., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Animals use the insulin/TOR signaling pathway to mediate their response to fluctuations in nutrient availability. Energy and amino acids are monitored at the single-cell level via the TOR branch of the pathway and systemically via insulin signaling to regulate cellular growth and metabolism. Using a combination of genetics, expression profiling, and chromatin immunoprecipitation, we examine nutritional control of gene expression and identify the transcription factor Myc as an important mediator of TOR-dependent regulation of ribosome biogenesis. We also identify myc as a direct target of FOXO and provide genetic evidence that Myc has a key role in mediating the effects of TOR and FOXO on growth and metabolism. FOXO and TOR also converge to regulate protein synthesis, acting via 4E-BP and Lk6, regulators of the translation factor eIF4E. This study uncovers a network of convergent regulation of protein biosynthesis by the FOXO and TOR branches of the nutrient-sensing pathway.

We have found that the Drosophila gene vps25 possesses several properties of a tumor suppressor. First, vps25 mutant cells activate Notch and Dpp receptor signaling, inducing ectopic organizers in developing eyes and limbs and consequent overproliferation of both mutant and nearby wild-type cells. Second, as the mutant cells proliferate, they lose their epithelial organization and undergo apoptosis. Strikingly, when apoptosis of mutant cells is blocked, tumor-like overgrowths are formed that are capable of metastasis. vps25 encodes a component of the ESCRT-II complex, which sorts membrane proteins into multivesicular bodies during endocytic trafficking to the lysosome. Activation of Notch and Dpp receptor signaling in mutant cells results from an endocytic blockage that causes accumulation of these receptors and other signaling components in endosomes. These results highlight the importance of endocytic trafficking in regulating signaling and epithelial organization and suggest a possible role for ESCRT components in human cancer.

The insulin/PI3K signaling pathway controls both tissue growth and metabolism. Here, we identify Melted as a new modulator of this pathway in Drosophila. Melted interacts with both Tsc1 and FOXO and can recruit these proteins to the cell membrane. We provide evidence that in the melted mutant, TOR activity is reduced and FOXO is activated. The melted mutant condition mimics the effects of nutrient deprivation in a normal animal, producing an animal with 40% less fat than normal.

The glypican family of heparan sulfate proteoglycans has been implicated in formation of morphogen gradients. Here, we examine the role of the glypican Dally-like protein (Dlp) in shaping the Wingless gradient in the Drosophila wing disc. Surprisingly, we find that Dlp has opposite effects at high and low levels of Wingless. Dlp promotes low-level Wingless activity but reduces high-level Wingless activity. We present evidence that the Wg antagonist Notum acts to induce cleavage of the Dlp glypican at the level of its GPI anchor, which leads to shedding of Dlp. Thus, spatially regulated modification of Dlp by Notum employs the ligand binding activity of Dlp to promote or inhibit signaling in a context-dependent manner. Notum-induced shedding of Dlp could convert Dlp from a membrane-tethered coreceptor to a secreted antagonist.

During development of multicellular organisms, cells are often eliminated by apoptosis if they fail to receive appropriate signals from their surroundings. Here, we report on short-range cell interactions that support cell survival in the Drosophila wing imaginal disc. We present evidence showing that cells incorrectly specified for their position undergo apoptosis because they fail to express specific proteins that are found on surrounding cells, including the LRR transmembrane proteins Capricious and Tartan. Interestingly, only the extracellular domains of Capricious and Tartan are required, suggesting that a bidirectional process of cell communication is involved in triggering apoptosis. We also present evidence showing that activation of the Notch signal transduction pathway is involved in triggering apoptosis of cells misspecified for their dorsal-ventral position.

The secreted signaling protein Wingless acts as a morphogen to pattern the imaginal discs of Drosophila. Here we report identification of a secreted repressor of Wingless activity, which we call Notum. Loss of Notum function leads to increased Wingless activity by altering the shape of the Wingless protein gradient. When overexpressed, Notum blocks Wingless activity. Notum encodes a member of the alpha/beta-hydrolase superfamily, with similarity to pectin acetylesterases. We present evidence that Notum influences Wingless protein distribution by modifying the heparan sulfate proteoglycans Dally-like and Dally. High levels of Wingless signaling induce Notum expression. Thus, Wingless contributes to shaping its own gradient by regulating expression of a protein that modifies its interaction with cell surface proteoglycans.

Studies in Drosophila have characterized insulin receptor/phosphoinositide 3-kinase (Inr/PI3K) signaling as a potent regulator of cell growth, but its function during development has remained uncertain. Here we show that inhibiting Inr/PI3K signaling phenocopies the cellular and organismal effects of starvation, whereas activating this pathway bypasses the nutritional requirement for cell growth, causing starvation sensitivity at the organismal level. Consistent with these findings, studies using a pleckstrin homology domain-green fluorescent protein (PH-GFP) fusion as an indicator for PI3K activity show that PI3K is regulated by the availability of dietary protein in vivo. Hence we surmise that an essential function of insulin/PI3K signaling in Drosophila is to coordinate cellular metabolism with nutritional conditions.