Drosophila unpaired encodes a secreted protein that activates the JAK signaling pathway

JAK/STAT signaling is involved in air sac primordium development of Drosophila melanogaster

The dorsal thoracic air sacs in fruit flies (Drosophila melanogaster) are functionally and developmentally comparable to human lungs. The progenitors of these structures, air sac primordia (ASPs), invasively propagate into wing imaginal disks, employing mechanisms similar to those that promote metastasis in malignant tumors. We investigated whether Janus kinase/signal transducer and activator of transcription JAK/STAT signaling plays a role in the directed morphogenesis of ASPs. We find that JAK/STAT signaling occurs in ASP tip cells and misexpression of core components in the JAK/STAT signaling cascade significantly impedes ASP development. We further identify Upd2 as an activating ligand for JAK/STAT activity in the ASP. Together, these data constitute a considerable step forward in understanding the role of JAK/STAT signaling in ASPs and similar structures in mammalian models.

Effects of unpaired 1 gene overexpression on the lifespan of Drosophila melanogaster

Background

The JAK/STAT signaling pathway is involved in many aging-related cellular functions. However, effects of overexpression of genes controlling JAK/STAT signal transduction on longevity of model organisms have not been studied. Here we evaluate the effect of overexpression of the unpaired 1 (upd1) gene, which encodes an activating ligand for JAK/STAT pathway, on the lifespan of Drosophila melanogaster.

Results

Overexpression of upd1 in the intestine caused a pronounced shortening of the median lifespan by 54.1–18.9%, and the age of 90% mortality by 40.9–19.1% in males and females, respectively. In fat body and in nervous system of male flies, an induction of upd1 overexpression increased the age of 90% mortality and median lifespan, respectively. An increase in upd1 expression enhanced mRNA levels of the JAK/STAT target genes domeless and Socs36E.

Conclusions

Conditional overexpression of upd1 in different tissues of Drosophila imago induces pro-aging or pro-longevity effects in tissue-dependent manner. The effects of upd1 overexpression on lifespan are accompanied by the transcription activation of genes for the components of JAK/STAT pathway.

JAK/STAT signaling in stem cells and regeneration: from Drosophila to vertebrates

The JAK/STAT pathway is a conserved metazoan signaling system that transduces cues from extracellular cytokines into transcriptional changes in the nucleus. JAK/STAT signaling is best known for its roles in immunity. However, recent work has demonstrated that it also regulates critical homeostatic processes in germline and somatic stem cells, as well as regenerative processes in several tissues, including the gonad, intestine and appendages. Here, we provide an overview of JAK/STAT signaling in stem cells and regeneration, focusing on Drosophila and highlighting JAK/STAT pathway functions in proliferation, survival and cell competition that are conserved between Drosophila and vertebrates.

Drosophila Jak/STAT Signaling: Regulation and Relevance in Human Cancer and Metastasis

Over the past three-decades, Janus kinase (Jak) and signal transducer and activator of transcription (STAT) signaling has emerged as a paradigm to understand the involvement of signal transduction in development and disease pathology. At the molecular level, cytokines and interleukins steer Jak/STAT signaling to transcriptional regulation of target genes, which are involved in cell differentiation, migration, and proliferation. Jak/STAT signaling is involved in various types of blood cell disorders and cancers in humans, and its activation is associated with carcinomas that are more invasive or likely to become metastatic. Despite immense information regarding Jak/STAT regulation, the signaling network has numerous missing links, which is slowing the progress towards developing drug therapies. In mammals, many components act in this cascade, with substantial cross-talk with other signaling pathways. In Drosophila, there are fewer pathway components, which has enabled significant discoveries regarding well-conserved regulatory mechanisms. Work across species illustrates the relevance of these regulators in humans. In this review, we showcase fundamental Jak/STAT regulation mechanisms in blood cells, stem cells, and cell motility. We examine the functional relevance of key conserved regulators from Drosophila to human cancer stem cells and metastasis. Finally, we spotlight less characterized regulators of Drosophila Jak/STAT signaling, which stand as promising candidates to be investigated in cancer biology. These comparisons illustrate the value of using Drosophila as a model for uncovering the roles of Jak/STAT signaling and the molecular means by which the pathway is controlled.

The Fly Way of Antiviral Resistance and Disease Tolerance

Like humans, insects face the threat of viral infection. Despite having repercussions on human health and disease, knowledge gaps exist for how insects cope with viral pathogens. Drosophila melanogaster serves as an ideal insect model due to its genetic tractability. When encountering a pathogen, two major approaches to fight disease are resistance strategies and tolerance strategies. Disease resistance strategies promote the health of the infected host by reducing pathogen load. Multiple disease resistance mechanisms have been identified in Drosophila: RNA interference, Jak/STAT signaling, Toll signaling, IMD signaling, and autophagy. Disease tolerance mechanisms, in contrast, do not reduce pathogen load directly, but rather mitigate the stress and damage incurred by infection. The main benefit of tolerance mechanisms may therefore be to provide the host with time to engage antiviral resistance mechanisms that eliminate the threat. In this review, antiviral resistance mechanisms used by Drosophila will be described and compared to mammalian antiviral mechanisms. Disease tolerance will then be explained in a broader context as this is a burgeoning field of study.

Growth and size control during development

The size and shape of organs are characteristic for each species. Even when organisms develop to different sizes due to varying environmental conditions, such as nutrition, organ size follows species-specific rules of proportionality to the rest of the body, a phenomenon referred to as allometry. Therefore, for a given environment, organs stop growth at a predictable size set by the species's genotype. How do organs stop growth? How can related species give rise to organs of strikingly different size? No definitive answer has been given to date. One of the major models for the studies of growth termination is the vinegar fly Drosophila melanogaster. Therefore, this review will focus mostly on work carried out in Drosophila to try to tease apart potential mechanisms and identify routes for further investigation. One general rule, found across the animal kingdom, is that the rate of growth declines with developmental time. Therefore, answers to the problem of growth termination should explain this seemingly universal fact. In addition, growth termination is intimately related to the problems of robustness (i.e. precision) and plasticity in organ size, symmetric and asymmetric organ development, and of how the ‘target’ size depends on extrinsic, environmental factors.

Analysis of NFKB2‑mediated regulation of mechanisms underlying the development of Hodgkin's lymphoma

Nuclear factor-κB (NF-κB) is widely involved in various lymphoid malignancies. However, its exact functional role and potential regulatory mechanisms in Hodgkin's lymphoma (HL) remains unclear. The present study aimed to investigate the regulatory mechanism of NF-κB in HL by analysis of a gene expression profile that was obtained from HL cells with or without NF-κB subunit 2 (NFKB2) knockdown. The GSE64234 dataset containing 6 HL cell line specimens transfected with small interfering (si)RNA against NFKB2 and 6 control specimens transfected with non-targeting siRNA sequences was downloaded from the Gene Expression Omnibus database. Based on these data, differentially expressed genes (DEGs) were screened for following data preprocessing. Functional enrichment analysis was subsequently conducted among the identified upregulated and downregulated DEGs. Additionally, a protein-protein interaction (PPI) network was constructed and module analyses were performed. Finally, microRNAs (miRNAs/miRs) targeting the identified DEGs were predicted for the construction of a miRNA-target regulatory network. A total of 253 DEGs were identified, consisting of 109 upregulated and 144 downregulated DEGs. Pathway enrichment analysis revealed that B-cell lymphoma 2-like 1 (BCL2L1) was significantly enriched in the NF-κB signaling pathway, and colony-stimulating factor 2 (CSF2) and BCL2L1 were enriched in the Jak-signal transducer and activator of transcription (STAT) signaling pathway. BCL2L1 and CSF2 were determined to be hub genes in the PPI network. A total of 6 miRNAs, including let-7a-5p, miR-9-5p, miR-155-5p, miR-135a-5p, miR-17-5p and miR-375, were identified in the miRNA-target regulatory network. The results of the present study indicated that NFKB2 may be involved in HL development through regulation of BCL2L1, CSF2, miR-135a-5p, miR-155-5p and miR-9-5p expression, as well as the modulation of Jak-STAT and NF-κB signaling pathways.

Cytokine receptor-Eb1 interaction couples cell polarity and fate during asymmetric cell division

Asymmetric stem cell division is a critical mechanism for balancing self-renewal and differentiation. Adult stem cells often orient their mitotic spindle to place one daughter inside the niche and the other outside of it to achieve asymmetric division. It remains unknown whether and how the niche may direct division orientation. Here we discover a novel and evolutionary conserved mechanism that couples cell polarity to cell fate. We show that the cytokine receptor homolog Dome, acting downstream of the niche-derived ligand Upd, directly binds to the microtubule-binding protein Eb1 to regulate spindle orientation in Drosophila male germline stem cells (GSCs). Dome’s role in spindle orientation is entirely separable from its known function in self-renewal mediated by the JAK-STAT pathway. We propose that integration of two functions (cell polarity and fate) in a single receptor is a key mechanism to ensure an asymmetric outcome following cell division.

JAK/STAT signaling prevents excessive apoptosis to ensure maintenance of the interfollicular stalk critical for Drosophila oogenesis

Apoptosis not only eliminates cells that are damaged or dangerous but also cells whose function during development in patterning or organogenesis is complete. The successful formation of germ cells is essential for the perpetuation of a species. The production of an oocyte often depends on signaling between germline and somatic cells, but also between specialized types of somatic cells. In Drosophila, each developing egg chamber is separated from the next by a single file of interfollicular somatic cells. Little is known about the function of the interfollicular stalk, although its presumed role in separating egg chambers is to ensure that patterning cues from one egg chamber do not impact or disrupt the development of adjacent egg chambers. We found that cells comprising the stalk undergo a progressive decrease in number during oogenesis through an apoptotic-dependent loss. The extent of programmed cell death is restricted by JAK/STAT signaling in a cell-autonomous manner to ensure that the stalk is maintained. Both a failure to undergo the normal reduction in stalk cell number, or to prevent excessive stalk cell apoptosis results in a decrease in fecundity. Thus, activation of JAK/STAT signaling in the Drosophila interfollicular stalk emerges as a model to study the tight regulation of signaling-dependent apoptosis.

Growth control in the Drosophila eye disc by the cytokine Unpaired

A fundamental question in developmental biology is how organ size is controlled. We have previously shown that the area growth rate in the Drosophila eye primordium declines inversely proportionally to the increase in its area. How the observed reduction in the growth rate is achieved is unknown. Here, we explore the dilution of the cytokine Unpaired (Upd) as a possible candidate mechanism. In the developing eye, upd expression is transient, ceasing at the time when the morphogenetic furrow first emerges. We confirm experimentally that the diffusion and stability of the JAK/STAT ligand Upd are sufficient to control eye disc growth via a dilution mechanism. We further show that sequestration of Upd by ectopic expression of an inactive form of the receptor Domeless (Dome) results in a substantially lower growth rate, but the area growth rate still declines inversely proportionally to the area increase. This growth rate-to-area relationship is no longer observed when Upd dilution is prevented by the continuous, ectopic expression of Upd. We conclude that a mechanism based on the dilution of the growth modulator Upd can explain how growth termination is controlled in the eye disc.

Canonical and non-canonical JAK/STAT transcriptional targets may be involved in distinct and overlapping cellular processes

Background

The Janus kinase-signal transducer and activator of transcription (JAK/STAT) pathway has been well-characterized as a crucial signal transduction cascade that regulates vital biological responses including development, immunity and oncogenesis. Additionally to its canonical pathway that uses the phosphorylated form of the STAT transcription factor, recently the non-canonical pathway involving heterochromatin formation by unphosphorylated STAT was recently uncovered. Considering the significant role of the JAK/STAT pathway, we used the simple Drosophila system in which the non-canonical pathway was initially characterized, to compare putative canonical versus non-canonical transcriptional targets across the genome. We analyzed microarray expression patterns of wildtype, Jak gain- and loss-of-function mutants, as well as the Stat loss-of-function mutant during embryogenesis, since the contribution of the canonical signal transduction pathway has been well-characterized in these contexts. Previous studies have also demonstrated that Jak gain-of-function and Stat mutants counter heterochromatin silencing to de-repress target genes by the non-canonical pathway.

Results

Compared to canonical target genomic loci, non-canonical targets were significantly more associated with sites enriched with heterochromatin-related factors (p = 0.004). Furthermore, putative canonical and non-canonical transcriptional targets identified displayed some differences in biological pathways they regulate, as determined by Gene Ontology (GO) enrichment analyses. Canonical targets were enriched mainly with genes relevant to development and immunity, as expected, whereas the non-canonical target gene set mainly showed enrichment of genes for various metabolic responses and stress response, highlighting the possibility that some differences may exist between the two loci.

Conclusions

Canonical and non-canonical JAK/STAT genes may regulate distinct and overlapping sets of genes and may perform specific overall functions in physiology. Further studies at different developmental stages, or using distinct tissues may identify additional targets and provide insight into which gene targets are unique to the canonical or non-canonical pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4058-y) contains supplementary material, which is available to authorized users.

Binding of a C-type lectin's coiled-coil domain to the Domeless receptor directly activates the JAK/STAT pathway in the shrimp immune response to bacterial infection

C-type lectins (CTLs) are characterized by the presence of a C-type carbohydrate recognition domain (CTLD) that by recognizing microbial glycans, is responsible for their roles as pattern recognition receptors in the immune response to bacterial infection. In addition to the CTLD, however, some CTLs display additional domains that can carry out effector functions, such as the collagenous domain of the mannose-binding lectin. While in vertebrates, the mechanisms involved in these effector functions have been characterized in considerable detail, in invertebrates they remain poorly understood. In this study, we identified in the kuruma shrimp (Marsupenaeus japonicus) a structurally novel CTL (MjCC-CL) that in addition to the canonical CTLD, contains a coiled-coil domain (CCD) responsible for the effector functions that are key to the shrimp's antibacterial response mediated by antimicrobial peptides (AMPs). By the use of in vitro and in vivo experimental approaches we elucidated the mechanism by which the recognition of bacterial glycans by the CTLD of MjCC-CL leads to activation of the JAK/STAT pathway via interaction of the CCD with the surface receptor Domeless, and upregulation of AMP expression. Thus, our study of the shrimp MjCC-CL revealed a striking functional difference with vertebrates, in which the JAK/STAT pathway is indirectly activated by cell death and stress signals through cytokines or growth factors. Instead, by cross-linking microbial pathogens with the cell surface receptor Domeless, a lectin directly activates the JAK/STAT pathway, which plays a central role in the shrimp antibacterial immune responses by upregulating expression of selected AMPs.

Chronic activation of JNK JAK/STAT and oxidative stress signalling causes the loser cell status

Cell competition is a form of cell interaction that causes the elimination of less fit cells, or losers, by wild-type (WT) cells, influencing overall tissue health. Several mutations can cause cells to become losers; however, it is not known how. Here we show that Drosophila wing disc cells carrying functionally unrelated loser mutations (Minute and mahjong) display the common activation of multiple stress signalling pathways before cell competition and find that these pathways collectively account for the loser status. We find that JNK signalling inhibits the growth of losers, while JAK/STAT signalling promotes competition-induced winner cell proliferation. Furthermore, we show that losers display oxidative stress response activation and, strikingly, that activation of this pathway alone, by Nrf2 overexpression, is sufficient to prime cells for their elimination by WT neighbours. Since oxidative stress and Nrf2 are linked to several diseases, cell competition may occur in a number of pathological conditions.Cell competition causes the removal of less fit cells ('losers') but why some gene mutations turn cells into losers is unclear. Here, the authors show that Drosophila wing disc cells carrying some loser mutations activate Nrf2 and JNK signalling, which contribute to the loser status.

The immediate early protein WSV187 can influence viral replication via regulation of JAK/STAT pathway in Drosophila

The world production of shrimp is seriously affected by the white spot syndrome virus (WSSV). Viral immediate-early (IE) genes encode regulatory proteins critical for the viral lifecycle. In spite of their importance, only five out of the 21 identified WSSV IE genes are functionally characterized. Here, we report the use of Drosophila melanogaster as a model to explore the role of WSSV IE gene wsv187. In vivo expression of WSV187 in transgenic flies show WSV187 localized in the cytoplasm. Overexpression of wsv187 results wing defects consistent with phenotypes observed in JAK/STAT exacerbated flies. After artificial infection of the DCV virus, the flies expressing wsv187 showed a lower viral load, a higher survival rate and an up-regulated STAT92E expression. These data demonstrate wsv187 plays a role in the controlling of virus replication by activating host JAK/STAT pathway.

Spatiotemporal regulation of cell fusion by JNK and JAK/STAT signaling during Drosophila wound healing

Cell-cell fusion is widely observed during development and disease, and imposes a dramatic change on participating cells. Cell fusion should be tightly controlled, but the underlying mechanism is poorly understood. Here, we found that the JAK/STAT pathway suppressed cell fusion during wound healing in the Drosophila larval epidermis, restricting cell fusion to the vicinity of the wound. In the absence of JAK/STAT signaling, a large syncytium containing a 3-fold higher number of nuclei than observed in wild-type tissue formed in wounded epidermis. The JAK/STAT ligand-encoding genes upd2 and upd3 were transcriptionally induced by wounding, and were required for suppressing excess cell fusion. JNK (also known as Basket in flies) was activated in the wound vicinity and activity peaked at ∼8 h after injury, whereas JAK/STAT signaling was activated in an adjoining concentric ring and activity peaked at a later stage. Cell fusion occurred primarily in the wound vicinity, where JAK/STAT activation was suppressed by fusion-inducing JNK signaling. JAK/STAT signaling was both necessary and sufficient for the induction of βPS integrin (also known as Myospheroid) expression, suggesting that the suppression of cell fusion was mediated at least in part by integrin protein.

Tissue-Intrinsic Tumor Hotspots: Terroir for Tumorigenesis

Epithelial tissues are highly organized systems with a remarkable homeostatic ability to maintain morphology through regulation of cellular proliferation and tissue integrity. This robust self-organizing system is progressively disrupted during tumor development. Recent studies of conserved tumor-suppressor genes in Drosophila showed how protumor cells deviate from the robustly organized tissue microenvironment to take the first steps into becoming aggressive tumors. Here we review the 'tumor hotspot' hypothesis that explains how the tissue-intrinsic local microenvironment has a pivotal role in the initial stage of tumorigenesis in Drosophila epithelia and discuss comparable mechanisms in mammalian tissues.

STAT5-Interacting Proteins: A Synopsis of Proteins that Regulate STAT5 Activity

Signal Transducers and Activators of Transcription (STATs) are key components of the JAK/STAT pathway. Of the seven STATs, STAT5A and STAT5B are of particular interest for their critical roles in cellular differentiation, adipogenesis, oncogenesis, and immune function. The interactions of STAT5A and STAT5B with cytokine/hormone receptors, nuclear receptors, transcriptional regulators, proto-oncogenes, kinases, and phosphatases all contribute to modulating STAT5 activity. Among these STAT5 interacting proteins, some serve as coactivators or corepressors to regulate STAT5 transcriptional activity and some proteins can interact with STAT5 to enhance or repress STAT5 signaling. In addition, a few STAT5 interacting proteins have been identified as positive regulators of STAT5 that alter serine and tyrosine phosphorylation of STAT5 while other proteins have been identified as negative regulators of STAT5 via dephosphorylation. This review article will discuss how STAT5 activity is modulated by proteins that physically interact with STAT5.

Tick Humoral Responses: Marching to the Beat of a Different Drummer

Ticks transmit a variety of human pathogens, including Borrelia burgdorferi, the etiological agent of Lyme disease. Multiple pathogens that are transmitted simultaneously, termed “coinfections,” are of increasing importance and can affect disease outcome in a host. Arthropod immunity is central to pathogen acquisition and transmission by the tick. Pattern recognition receptors recognize pathogen-associated molecular patterns and induce humoral responses through the Toll and Immune Deficiency (IMD) pathways. Comparative analyses between insects and ticks reveal that while the Toll pathway is conserved, the IMD network exhibits a high degree of variability. This indicates that major differences in humoral immunity exist between insects and ticks. While many variables can affect immunity, one of the major forces that shape immune outcomes is the microbiota. In light of this, we discuss how the presence of commensal bacteria, symbionts and/or coinfections can lead to altered immune responses in the tick that impact pathogen persistence and subsequent transmission. By investigating non-insect arthropod immunity, we will not only better comprehend tick biology, but also unravel the intricate effects that pathogen coinfections have on vector competence and tick-borne disease transmission.

JAK/STAT controls organ size and fate specification by regulating morphogen production and signalling

A stable pool of morphogen-producing cells is critical for the development of any organ or tissue. Here we present evidence that JAK/STAT signalling in the Drosophila wing promotes the cycling and survival of Hedgehog-producing cells, thereby allowing the stable localization of the nearby BMP/Dpp-organizing centre in the developing wing appendage. We identify the inhibitor of apoptosis dIAP1 and Cyclin A as two critical genes regulated by JAK/STAT and contributing to the growth of the Hedgehog-expressing cell population. We also unravel an early role of JAK/STAT in guaranteeing Wingless-mediated appendage specification, and a later one in restricting the Dpp-organizing activity to the appendage itself. These results unveil a fundamental role of the conserved JAK/STAT pathway in limb specification and growth by regulating morphogen production and signalling, and a function of pro-survival cues and mitogenic signals in the regulation of the pool of morphogen-producing cells in a developing organ.

Dissecting cellular senescence and SASP in Drosophila

Cellular senescence can act as both tumor suppressor and tumor promoter depending on the cellular contexts. On one hand, premature senescence has been considered as an innate host defense mechanism against carcinogenesis in mammals. In response to various stresses including oxidative stress, DNA damage, and oncogenic stress, suffered cells undergo irreversible cell cycle arrest, leading to tumor suppression. On the other hand, recent studies in mammalian systems have revealed that senescent cells can drive oncogenesis by secreting diverse proteins such as inflammatory cytokines, matrix remodeling factors, and growth factors, the phenomenon called senescence-associated secretory phenotype (SASP). However, the mechanisms by which these contradictory effects regulate tumor growth and metastasis in vivo have been elusive. Here, we review the recent discovery of cellular senescence in Drosophila and the mechanisms underlying senescence-mediated tumor regulation dissected by Drosophila genetics.

Annotation of the Asian Citrus Psyllid Genome Reveals a Reduced Innate Immune System

Citrus production worldwide is currently facing significant losses due to citrus greening disease, also known as Huanglongbing. The citrus greening bacteria, Candidatus Liberibacter asiaticus (CLas), is a persistent propagative pathogen transmitted by the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). Hemipterans characterized to date lack a number of insect immune genes, including those associated with the Imd pathway targeting Gram-negative bacteria. The D. citri draft genome was used to characterize the immune defense genes present in D. citri. Predicted mRNAs identified by screening the published D. citri annotated draft genome were manually searched using a custom database of immune genes from previously annotated insect genomes. Toll and JAK/STAT pathways, general defense genes Dual oxidase, Nitric oxide synthase, prophenoloxidase, and cellular immune defense genes were present in D. citri. In contrast, D. citri lacked genes for the Imd pathway, most antimicrobial peptides, 1,3-β-glucan recognition proteins (GNBPs), and complete peptidoglycan recognition proteins. These data suggest that D. citri has a reduced immune capability similar to that observed in A. pisum, P. humanus, and R. prolixus. The absence of immune system genes from the D. citri genome may facilitate CLas infections, and is possibly compensated for by their relationship with their microbial endosymbionts.

Actin is an evolutionarily-conserved damage-associated molecular pattern that signals tissue injury in Drosophila melanogaster

Damage-associated molecular patterns (DAMPs) are molecules released by dead cells that trigger sterile inflammation and, in vertebrates, adaptive immunity. Actin is a DAMP detected in mammals by the receptor, DNGR-1, expressed by dendritic cells (DCs). DNGR-1 is phosphorylated by Src-family kinases and recruits the tyrosine kinase Syk to promote DC cross-presentation of dead cell-associated antigens. Here we report that actin is also a DAMP in invertebrates that lack DCs and adaptive immunity. Administration of actin to Drosophila melanogaster triggers a response characterised by selective induction of STAT target genes in the fat body through the cytokine Upd3 and its JAK/STAT-coupled receptor, Domeless. Notably, this response requires signalling via Shark, the Drosophila orthologue of Syk, and Src42A, a Drosophila Src-family kinase, and is dependent on Nox activity. Thus, extracellular actin detection via a Src-family kinase-dependent cascade is an ancient means of detecting cell injury that precedes the evolution of adaptive immunity.

β-Arrestin 1's Interaction with TC45 Attenuates Stat signaling by dephosphorylating Stat to inhibit antimicrobial peptide expression

Impaired phosphatase activity leads to the persistent activation of signal transducers and activators of transcription (Stat). In mammals, Stat family members are often phosphorylated or dephosphorylated by the same enzymes. To date, only one Stat similar to mammalian Stat5a/b has been found in crustaceans and there have been few studies in Stat signal regulation in crustaceans. Here, we report that β-arrestin1 interacts with TC45 (45-kDa form of T cell protein tyrosine phosphatase) in the nucleus to attenuate Stat signaling by promoting dephosphorylation of Stat. Initially, we showed that Stat translocates into the nucleus to induce antimicrobial peptide (AMP) expression after bacterial infection. βArr1 enters the nucleus of hemocytes and recruits TC45 to form the βarr1-TC45-Stat complex, which dephosphorylates Stat efficiently. The interaction of TC45 with Stat decreased and Stat phosphorylation increased in βarr1-silenced shrimp (Marsupenaeus japonicus) after challenge with Vibrio anguillarum. βArr1 directly interacts with Stat in nucleus and accelerates Stat dephosphorylation by recruiting TC45 after V. anguillarum challenge. Further study showed that βarr1 and TC45 also affect AMP expression, which is regulated by Stat. Therefore, βarr1 and TC45 are involved in the anti-V. anguillarum immune response by regulating Stat activity negatively to decrease AMP expression in shrimp.

Epithelial Tumors Originate in Tumor Hotspots, a Tissue-Intrinsic Microenvironment

Malignant tumors are caused by uncontrolled proliferation of transformed mutant cells that have lost the ability to maintain tissue integrity. Although a number of causative genetic backgrounds for tumor development have been discovered, the initial steps mutant cells take to escape tissue integrity and trigger tumorigenesis remain elusive. Here, we show through analysis of conserved neoplastic tumor-suppressor genes (nTSGs) in Drosophila wing imaginal disc epithelia that tumor initiation depends on tissue-intrinsic local cytoarchitectures, causing tumors to consistently originate in a specific region of the tissue. In this “tumor hotspot” where cells constitute a network of robust structures on their basal side, nTSG-deficient cells delaminate from the apical side of the epithelium and begin tumorigenic overgrowth by exploiting endogenous Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling activity. Conversely, in other regions, the “tumor coldspot” nTSG-deficient cells are extruded toward the basal side and undergo apoptosis. When the direction of delamination is reversed through suppression of RhoGEF2, an activator of the Rho family small GTPases, and JAK/STAT is activated ectopically in these coldspot nTSG-deficient cells, tumorigenesis is induced. These data indicate that two independent processes, apical delamination and JAK/STAT activation, are concurrently required for the initiation of nTSG-deficient-induced tumorigenesis. Given the conservation of the epithelial cytoarchitecture, tumorigenesis may be generally initiated from tumor hotspots by a similar mechanism.

A genetic study in Drosophila reveals a mechanism of tumorigenesis by which pro-tumor cells initiate dysplastic tumor growth at specific "hotspot" locations in epithelial tissues.

Transformed mutant cells (pro-tumor cells) can evolve through a multistep process in which they become tumorigenic and invasive. Many genes that are involved in the different steps towards cancer development have been identified; however, how certain mutant cells destroy normal tissue organization and undergo uncontrolled proliferation during the initial stages of this process remains largely unclear. Using the epithelial tissue of the wing imaginal discs of the fruit fly (Drosophila melanogaster) larvae as a model system, we have analyzed these initial stages of inducing tumors by depletion of a neoplastic tumor suppressor gene (nTSG). We discovered that these tumors always originate from specific regions of the epithelial tissue of the wing disc. We show that in other regions that we dubbed “tumor coldspots” and that lack specific cellular structures, pro-tumor cells are eliminated from the epithelial tissue by the surrounding cells. However, in “tumor hotspots,” cells constitute specific structures in their basal side, and we found that pro-tumor cells successfully avoid potential elimination and deviate from the apical side of the tissue, initiating tumorous overgrowth. Our findings reveal the molecular and cellular mechanisms underlying the initial steps of tumorigenesis at tumor hotspots in the Drosophila imaginal wing discs.

Evolution of Cytokine Receptor Signaling

Cytokines represent essential mediators of cell–cell communication with particularly important roles within the immune system. These secreted factors are produced in response to developmental and/or environmental cues and act via cognate cytokine receptors on target cells, stimulating specific intracellular signaling pathways to facilitate appropriate cellular responses. This review describes the evolution of cytokine receptor signaling, focusing on the class I and class II receptor families and the downstream JAK–STAT pathway along with its key negative regulators. Individual components generated over a long evolutionary time frame coalesced to form an archetypal signaling pathway in bilateria that was expanded extensively during early vertebrate evolution to establish a substantial “core” signaling network, which has subsequently undergone limited diversification within discrete lineages. The evolution of cytokine receptor signaling parallels that of the immune system, particularly the emergence of adaptive immunity, which has likely been a major evolutionary driver.

The ins(ide) and outs(ide) of asymmetric stem cell division

Many adult stem cells divide asymmetrically, generating one stem cell (self-renewal) and one differentiating cell. Balancing self-renewal and differentiation is critical for sustaining tissue homeostasis throughout the life of an organism. Failure to execute asymmetric stem cell division can have profound impacts on tissue homeostasis, resulting in tissue degeneration or hyperplasia/tumorigenic overgrowth. Recent studies have expanded our understanding of both the extracellular and intracellular mechanisms that regulate, reinforce and ensure an asymmetric outcome following stem cell division. In this review, we discuss newly discovered aspects of asymmetric stem cell division that, in concert with well-established mechanisms, contribute to balancing self-renewal and differentiation.

Remote Control of Intestinal Stem Cell Activity by Haemocytes in Drosophila

The JAK/STAT pathway is a key signaling pathway in the regulation of development and immunity in metazoans. In contrast to the multiple combinatorial JAK/STAT pathways in mammals, only one canonical JAK/STAT pathway exists in Drosophila. It is activated by three secreted proteins of the Unpaired family (Upd): Upd1, Upd2 and Upd3. Although many studies have established a link between JAK/STAT activation and tissue damage, the mode of activation and the precise function of this pathway in the Drosophila systemic immune response remain unclear. In this study, we used mutations in upd2 and upd3 to investigate the role of the JAK/STAT pathway in the systemic immune response. Our study shows that haemocytes express the three upd genes and that injury markedly induces the expression of upd3 by the JNK pathway in haemocytes, which in turn activates the JAK/STAT pathway in the fat body and the gut. Surprisingly, release of Upd3 from haemocytes upon injury can remotely stimulate stem cell proliferation and the expression of Drosomycin-like genes in the intestine. Our results also suggest that a certain level of intestinal epithelium renewal is required for optimal survival to septic injury. While haemocyte-derived Upd promotes intestinal stem cell activation and survival upon septic injury, haemocytes are dispensable for epithelium renewal upon oral bacterial infection. Our study also indicates that intestinal epithelium renewal is sensitive to insults from both the lumen and the haemocoel. It also reveals that release of Upds by haemocytes coordinates the wound-healing program in multiple tissues, including the gut, an organ whose integrity is critical to fly survival.

Looking Beyond the Genes: The Interplay Between Signaling Pathways and Mechanics in the Shaping and Diversification of Epithelial Tissues

The core of Evo-Devo lies in the intuition that the way tissues grow during embryonic development, the way they sustain their structure and function throughout lifetime, and the way they evolve are closely linked. Epithelial tissues are ubiquitous in metazoans, covering the gut and internal branched organs, as well as the skin and its derivatives (ie, teeth). Here, we discuss in vitro, in vivo, and in silico studies on epithelial tissues to illustrate the conserved, dynamical, and complex aspects of their development. We then explore the implications of the dynamical and nonlinear nature of development on the evolution of their size and shape at the phenotypic and genetic levels. In rare cases, when the interplay between signaling and mechanics is well understood at the cell level, it is becoming clear that the structure of development leads to covariation of characters, an integration which in turn provides some predictable structure to evolutionary changes. We suggest that such nonlinear systems are prone to genetic drift, cryptic genetic variation, and context-dependent mutational effects. We argue that experimental and theoretical studies at the cell level are critical to our understanding of the phenotypic and genetic evolution of epithelial tissues, including carcinomas.

Tissue communication in a systemic immune response of Drosophila

Several signaling pathways, including the JAK/STAT and Toll pathways, are known to activate blood cells (hemocytes) in Drosophila melanogaster larvae. They are believed to regulate the immune response against infections by parasitoid wasps, such as Leptopilina boulardi, but how these pathways control the hemocytes is not well understood. Here, we discuss the recent discovery that both muscles and fat body take an active part in this response. Parasitoid wasp infection induces Upd2 and Upd3 secretion from hemocytes, leading to JAK/STAT activation mainly in hemocytes and in skeletal muscles. JAK/STAT activation in muscles, but not in hemocytes, is required for an efficient encapsulation of wasp eggs. This suggests that Upd2 and Upd3 are important cytokines, coordinating different tissues for the cellular immune response in Drosophila. In the fat body, Toll signaling initiates a systemic response in which hemocytes are mobilized and activated hemocytes (lamellocytes) are generated. However, the contribution of Toll signaling to the defense against wasps is limited, probably because the wasps inject inhibitors that prevent the activation of the Toll pathway. In conclusion, parasite infection induces a systemic response in Drosophila larvae involving major organ systems and probably the physiology of the entire organism.

Apontic regulates somatic stem cell numbers in Drosophila testes

BACKGROUND

Microenvironments called niches maintain resident stem cell populations by balancing self-renewal with differentiation, but the genetic regulation of this process is unclear. The niche of the Drosophila testis is well-characterized and genetically tractable, making it ideal for investigating the molecular regulation of stem cell biology. The JAK/STAT pathway, activated by signals from a niche component called the hub, maintains both germline and somatic stem cells.

RESULTS

This study investigated the molecular regulation of the JAK/STAT pathway in the stem cells of the Drosophila testis. We determined that the transcriptional regulator Apontic (Apt) acts in the somatic (cyst) stem cells (CySCs) to balance differentiation and maintenance. We found Apt functions as a negative feedback inhibitor of STAT activity, which enables cyst cell maturation. Simultaneous loss of the STAT regulators apt and Socs36E, or the Stat92E-targeting microRNA miR-279, expanded the somatic stem cell-like population.

CONCLUSIONS

Genetic analysis revealed that a conserved genetic regulatory network limits JAK/STAT activity in the somatic stem cells of Drosophila testis. In these cells, we determined JAK/STAT signaling promotes apt expression. Then, Apt functions through Socs36E and miR-279 to attenuate pathway activation, which is required for timely CySC differentiation. We propose that Apt acts as a core component of a STAT-regulatory circuit to prevent stem cell overpopulation and allow stem cell maturation.

Cytokines in Drosophila immunity

Cytokines are a large and diverse group of small proteins that can affect many biological processes, but most commonly cytokines are known as mediators of the immune response. In the event of an infection, cytokines are produced in response to an immune stimulus, and they function as key regulators of the immune response. Cytokines come in many shapes and sizes, and although they vary greatly in structure, their functions have been well conserved in evolution. The immune signaling pathways that respond to cytokines are remarkably conserved from fly to man. Therefore, Drosophila melanogaster, provides an excellent platform for studying the biology and function of cytokines. In this review, we will describe the cytokines and cytokine-like molecules found in the fly and discuss their roles in host immunity.

Mechanisms of JAK/STAT pathway negative regulation by the short coreceptor Eye Transformer/Latran

The short receptor Et/Lat negatively regulates Drosophila JAK/STAT signaling. It binds to intracellular components and the Domeless receptor but cannot bind ligands, thus generating a signaling-incompetent complex. Et/Lat is also more stable than Dome. The study provides insights into how short receptors negatively regulate signaling.

Transmembrane receptors interact with extracellular ligands to transduce intracellular signaling cascades, modulate target gene expression, and regulate processes such as proliferation, apoptosis, differentiation, and homeostasis. As a consequence, aberrant signaling events often underlie human disease. Whereas the vertebrate JAK/STAT signaling cascade is transduced via multiple receptor combinations, the Drosophila pathway has only one full-length signaling receptor, Domeless (Dome), and a single negatively acting receptor, Eye Transformer/Latran (Et/Lat). Here we investigate the molecular mechanisms underlying Et/Lat activity. We demonstrate that Et/Lat negatively regulates the JAK/STAT pathway activity and can bind to Dome, thus reducing Dome:Dome homodimerization by creating signaling-incompetent Dome:Et/Lat heterodimers. Surprisingly, we find that Et/Lat is able to bind to both JAK and STAT92E but, despite the presence of putative cytokine-binding motifs, does not detectably interact with pathway ligands. We find that Et/Lat is trafficked through the endocytic machinery for lysosomal degradation but at a much slower rate than Dome, a difference that may enhance its ability to sequester Dome into signaling-incompetent complexes. Our data offer new insights into the molecular mechanism and regulation of Et/Lat in Drosophila that may inform our understanding of how short receptors function in other organisms.

Inositol phosphate kinase 2 is required for imaginal disc development in Drosophila

Inositol phosphate kinase 2 (Ipk2), also known as IP multikinase IPMK, is an evolutionarily conserved protein that initiates production of inositol phosphate intracellular messengers (IPs), which are critical for regulating nuclear and cytoplasmic processes. Here we report that Ipk2 kinase activity is required for the development of the adult fruit fly epidermis. Ipk2 mutants show impaired development of their imaginal discs, the primordial tissues that form the adult epidermis. Although disk tissue seems to specify normally during early embryogenesis, loss of Ipk2 activity results in increased apoptosis and impairment of proliferation during larval and pupal development. The proliferation defect is in part attributed to a reduction in JAK/STAT signaling, possibly by controlling production or secretion of the pathway's activating ligand, Unpaired. Constitutive activation of the JAK/STAT pathway downstream of Unpaired partially rescues the disk growth defects in Ipk2 mutants. Thus, IP production is essential for proliferation of the imaginal discs, in part, by regulating JAK/STAT signaling. Our work demonstrates an essential role for Ipk2 in producing inositide messengers required for imaginal disk tissue maturation and subsequent formation of adult body structures and provides molecular insights to signaling pathways involved in tissue growth and stability during development.

Multipotent versus differentiated cell fate selection in the developing Drosophila airways

Developmental potentials of cells are tightly controlled at multiple levels. The embryonic Drosophila airway tree is roughly subdivided into two types of cells with distinct developmental potentials: a proximally located group of multipotent adult precursor cells (P-fate) and a distally located population of more differentiated cells (D-fate). We show that the GATA-family transcription factor (TF) Grain promotes the P-fate and the POU-homeobox TF Ventral veinless (Vvl/Drifter/U-turned) stimulates the D-fate. Hedgehog and receptor tyrosine kinase (RTK) signaling cooperate with Vvl to drive the D-fate at the expense of the P-fate while negative regulators of either of these signaling pathways ensure P-fate specification. Local concentrations of Decapentaplegic/BMP, Wingless/Wnt, and Hedgehog signals differentially regulate the expression of D-factors and P-factors to transform an equipotent primordial field into a concentric pattern of radially different morphogenetic potentials, which gradually gives rise to the distal-proximal organization of distinct cell types in the mature airway.

DOI:http://dx.doi.org/10.7554/eLife.09646.001

Many organs are composed of tubes of different sizes, shapes and patterns that transport vital substances from one site to another. In the fruit fly species Drosophila melanogaster, oxygen is transported by a tubular network, which divides into finer tubes that allow the oxygen to reach every part of the body.

Different parts of the fruit fly’s airways develop from different groups of tracheal precursor cells. P-fate cells form the most 'proximal' tubes (which are found next to the outer layer of the fly). These cells are 'multipotent' stem cells, and have the ability to specialize into many different types of cells during metamorphosis. The more 'distal' branches that emerge from the proximal tubes develop from D-fate cells. These are cells that generally acquire a narrower range of cell identities.

By performing a genetic analysis of fruit fly embryos, Matsuda et al. have now identified several proteins and signaling molecules that control whether tracheal precursor cells become D-fate or P-fate cells. For example, several signaling pathways work with a protein called Ventral veinless to cause D-fate cells to develop instead of P-fate cells. However, molecules that prevent signaling occurring via these pathways help P-fate cells to form. Different amounts of the molecules that either promote or hinder these signaling processes are present in different parts of the fly embryo; this helps the airways of the fly to develop in the correct pattern.

This work provides a comprehensive view of how cell types with different developmental potentials are positioned in a complex tubular network. This sets a basis for future studies addressing how the respiratory organs – and indeed the entire organism – are sustained.

DOI:http://dx.doi.org/10.7554/eLife.09646.002

Wnt Signaling in Sexual Dimorphism

The embryonic gonad of Drosophila melanogaster begins to display sexually dimorphic traits soon after its formation. Here we demonstrate the involvement of a wnt family ligand, wnt-2, in the induction of these sex-specific differences. We show that wnt-2 contributes to the survival of a male-specific population of somatic gonadal precursor cells (SGPs), the male-specific SGPs that are located at the posterior of the male gonad. We also show that the Wnt-2 ligand synergizes with the JAK-STAT ligand Upd, which is produced by SGPs at the anterior of the gonad to activate the STAT pathway in male germ cells. We suggest that the use of two spatially separated signaling systems to initiate the JAK-STAT stem cell maintenance pathway in germ cells provides a mechanism for increasing the pool of potential progenitors of the germline stem cells in the adult testes. Finally, we present evidence indicating that, like the JAK-STAT pathway, wnt-2 stimulates germ cells in male embryos to re-enter the cell cycle.

JAK/STAT signaling in Drosophila muscles controls the cellular immune response against parasitoid infection

The role of JAK/STAT signaling in the cellular immune response of Drosophila is not well understood. Here, we show that parasitoid wasp infection activates JAK/STAT signaling in somatic muscles of the Drosophila larva, triggered by secretion of the cytokines Upd2 and Upd3 from circulating hemocytes. Deletion of upd2 or upd3, but not the related os (upd1) gene, reduced the cellular immune response, and suppression of the JAK/STAT pathway in muscle cells reduced the encapsulation of wasp eggs and the number of circulating lamellocyte effector cells. These results suggest that JAK/STAT signaling in muscles participates in a systemic immune defense against wasp infection.

Co-option of an Ancestral Hox-Regulated Network Underlies a Recently Evolved Morphological Novelty

The evolutionary origins of complex morphological structures such as the vertebrate eye or insect wing remain one of the greatest mysteries of biology. Recent comparative studies of gene expression imply that new structures are not built from scratch, but rather form by co-opting preexisting gene networks. A key prediction of this model is that upstream factors within the network will activate their preexisting targets (i.e., enhancers) to form novel anatomies. Here, we show how a recently derived morphological novelty present in the genitalia of D. melanogaster employs an ancestral Hox-regulated network deployed in the embryo to generate the larval posterior spiracle. We demonstrate how transcriptional enhancers and constituent transcription factor binding sites are used in both ancestral and novel contexts. These results illustrate network co-option at the level of individual connections between regulatory genes and highlight how morphological novelty may originate through the co-option of networks controlling seemingly unrelated structures.

Comparative analysis of zygotic developmental genes in Rhodnius prolixus genome shows conserved features on the tracheal developmental pathway

Most of the in-depth studies on insect developmental genetic have been carried out in the fruit fly Drosophila melanogaster, an holometabolous insect, so much more still remains to be studied in hemimetabolous insects. Having Rhodnius prolixus sequenced genome available, we search for orthologue genes of zygotic signaling pathways, segmentation, and tracheogenesis in the R. prolixus genome and in three species of Triatoma genus transcriptomes, concluding that there is a high level of gene conservation. We also study the function of two genes required for tracheal system development in D. melanogaster - R. prolixus orthologues: trachealess (Rp-trh) and empty spiracles (Rp-ems). From that we see that Rp-trh is required for early tracheal development since Rp-trh RNAi shows that the primary tracheal branches fail to form. On the other hand, Rp-ems is implied in the proper formation of the posterior tracheal branches, in a similar way to D. melanogaster. These results represent the initial characterization of the genes involved in the tracheal development of an hemimetabolous insect building a bridge between the current genomic era and V. Wigglesworth's classical studies on insects' respiratory system physiology.

Socs36E limits STAT signaling via Cullin2 and a SOCS-box independent mechanism in the Drosophila egg chamber

The Suppressor of Cytokine Signaling (SOCS) proteins are critical, highly conserved feedback inhibitors of signal transduction cascades. The family of SOCS proteins is divided into two groups: ancestral and vertebrate-specific SOCS proteins. Vertebrate-specific SOCS proteins have been heavily studied as a result of their strong mutant phenotypes. However, the ancestral clade remains less studied, a potential result of genetic redundancies in mammals. Use of the genetically tractable organism Drosophila melanogaster enables in vivo assessment of signaling components and mechanisms with less concern about the functional redundancy observed in mammals. In this study, we investigated how the SOCS family member Suppressor of Cytokine Signaling at 36E (Socs36E) attenuates Janus Kinase/Signal Transducer and Activator of Transcription (Jak/STAT) activation during specification of motile border cells in Drosophila oogenesis. We found that Socs36E genetically interacts with the Cullin2 (Cul2) scaffolding protein. Like Socs36E, Cul2 is required to limit the number of motile cells in egg chambers. We demonstrated that loss of Cul2 in the follicle cells significantly increased nuclear STAT protein levels, which resulted in additional cells acquiring invasive properties. Further, reduction of Cul2 suppressed border cell migration defects that occur in a Stat92E-sensitized genetic background. Our data incorporated Cul2 into a previously described Jak/STAT-directed genetic regulatory network that is required to generate a discrete boundary between cell fates. We also found that Socs36E is able to attenuate STAT activity in the egg chamber when it does not have a functional SOCS box. Collectively, this work contributes mechanistic insight to a Jak/STAT regulatory genetic circuit, and suggests that Socs36E regulates Jak/STAT signaling via a Cul2-dependent mechanism, as well as by a Cullin-independent manner, in vivo.

Identification of a JAK/STAT pathway receptor domeless from Pacific white shrimp Litopenaeus vannamei

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway was known to participate in dozens of immune responses in organisms. Domeless, first identified in Drosophila melanogaster, is a unique receptor involved in invertebrate JAK/STAT pathway. In this study, a cytokine receptor (LvDOME) was identified in Litopenaeus vannamei. The LvDOME cDNA was 5178bp in length with an Open Reading Frame (ORF) of 4191bp. LvDOME contained two cytokine binding modules (CBMs) and three fibronectin-type-III-like (FNIII) domains, similar to most vertebrate IL-6 receptors. LvDOME was expressed highest in shrimp muscle and could be up-regulated in the late stage of white spot syndrome virus (WSSV) infection. LvDOME could significantly enhance the activity of the WSSV wsv069 gene promoter through acting on the STAT-binding motif, suggesting LvDOME could activate the JAK/STAT pathway. Moreover, knockdown of LvDOME resulted in lower cumulative mortality of shrimps and less WSSV copies, suggesting LvDOME may be hijacked by WSSV to benefit virus replication. To our knowledge, this is the first report on the receptor of JAK/STAT pathway in shrimp.

Windpipe controls Drosophila intestinal homeostasis by regulating JAK/STAT pathway via promoting receptor endocytosis and lysosomal degradation

The adult intestinal homeostasis is tightly controlled by proper proliferation and differentiation of intestinal stem cells. The JAK/STAT (Janus Kinase/Signal Transducer and Activator of Transcription) signaling pathway is essential for the regulation of adult stem cell activities and maintenance of intestinal homeostasis. Currently, it remains largely unknown how JAK/STAT signaling activities are regulated in these processes. Here we have identified windpipe (wdp) as a novel component of the JAK/STAT pathway. We demonstrate that Wdp is positively regulated by JAK/STAT signaling in Drosophila adult intestines. Loss of wdp activity results in the disruption of midgut homeostasis under normal and regenerative conditions. Conversely, ectopic expression of Wdp inhibits JAK/STAT signaling activity. Importantly, we show that Wdp interacts with the receptor Domeless (Dome), and promotes its internalization for subsequent lysosomal degradation. Together, these data led us to propose that Wdp acts as a novel negative feedback regulator of the JAK/STAT pathway in regulating intestinal homeostasis.

Effective tissue homeostasis requires a proper balance between the removal of dead cells and production of new cells. Due to environmental challenges, the Drosophila midgut epithelial cells are damaged from time to time and intestinal stem cells (ISC) can accelerate their proliferative rate to replace the lost midgut epithelium. The JAK/STAT pathway plays essential roles in these progresses. Upon damage, Upd ligands produced by dying enterocytes (ECs) activate JAK/STAT signaling in ISCs to promote their proliferation and differentiation. However, after damage how JAK/STAT signaling is switched from a highly active state to a homeostatic state is not yet fully understood. In this study, we identified the leucine rich repeats (LRR) protein Windpipe (Wdp) as a novel negative feedback regulator of JAK/STAT signaling during intestinal development. Wdp expression was induced by high levels of JAK/STAT signaling in intestines. And loss of Wdp leads to midgut homeostasis loss and increased ISC proliferation. Furthermore, we found Wdp in turn negatively regulates JAK/STAT signaling activity through promoting Domeless receptor endocytosis and lysosomal degradation. In this way, high levels of JAK/STAT signaling is switched off by Wdp, which ensure ISCs return to the homeostatic state after tissue damage.

Reduction of T antigen causes loss of hematopoietic progenitors in Drosophila through the inhibition of filopodial extensions from the hematopoietic niche

Hematopoietic stem cells (HSCs) are present in hematopoietic organs and differentiate into mature blood cells as required. Defective HSCs have been implicated in the human autoimmune disease Tn syndrome, which results from the failure of the core 1 β1,3-galactosyltransferase 1 enzyme (C1β3GalT1) to synthesize T antigen. In both mice and humans, a reduced level of T antigen is associated with a reduction in blood cell numbers. However, the precise roles of T antigen in hematopoiesis are unknown. Here, we show that the Drosophila T antigen, supplied by plasmatocytes, is essential for the regulation of HSCs. T antigen appears to be an essential factor in maintaining the extracellular environment to support filopodial extensions from niches that are responsible for transmitting signaling molecules to maintain the HSCs. In addition, our results revealed that the clotting factor, hemolectin, disrupted the hemolymph environment of C1β3GalT1 mutants. This study identified a novel mucin function for the regulation of HSCs that may be conserved in other species.

The Hippo pathway regulates homeostatic growth of stem cell niche precursors in the Drosophila ovary

The Hippo pathway regulates organ size, stem cell proliferation and tumorigenesis in adult organs. Whether the Hippo pathway influences establishment of stem cell niche size to accommodate changes in organ size, however, has received little attention. Here, we ask whether Hippo signaling influences the number of stem cell niches that are established during development of the Drosophila larval ovary, and whether it interacts with the same or different effector signaling pathways in different cell types. We demonstrate that canonical Hippo signaling regulates autonomous proliferation of the soma, while a novel hippo-independent activity of Yorkie regulates autonomous proliferation of the germ line. Moreover, we demonstrate that Hippo signaling mediates non-autonomous proliferation signals between germ cells and somatic cells, and contributes to maintaining the correct proportion of these niche precursors. Finally, we show that the Hippo pathway interacts with different growth pathways in distinct somatic cell types, and interacts with EGFR and JAK/STAT pathways to regulate non-autonomous proliferation of germ cells. We thus provide evidence for novel roles of the Hippo pathway in establishing the precise balance of soma and germ line, the appropriate number of stem cell niches, and ultimately regulating adult female reproductive capacity.

During development, organ growth must be carefully regulated to make sure that organs achieve the correct final size needed for organ function. In organs that are made of many different types of cells, this growth regulation is likely to be particularly complex, because it is important for organs to have appropriate proportions, or relative numbers, of the different kinds of cells that make up the organ, as well as the correct number of total cells. One method that cells use to regulate organ growth is a signaling pathway called the Hippo pathway. However, Hippo signaling has been studied, to date, primarily in organ systems that are made up of one cell type. In this study, we examine how Hippo signaling can work to regulate the proportions of different types of cells, as well as the total number of cells in an organ. To do this, we used the developing ovary of the fruit fly as a study system. We found that (1) Hippo signaling regulates the proliferation of many different cell types of the ovary; and (2) Hippo signaling activity in one cell type influences proliferation of other cell types, thus ensuring appropriate proportions of different ovarian cell types.

Bacterial and fungal pattern recognition receptors in homologous innate signaling pathways of insects and mammals

In response to bacterial and fungal infections in insects and mammals, distinct families of innate immune pattern recognition receptors (PRRs) initiate highly complex intracellular signaling cascades. Those cascades induce a variety of immune functions that restrain the spread of microbes in the host. Insect and mammalian innate immune receptors include molecules that recognize conserved microbial molecular patterns. Innate immune recognition leads to the recruitment of adaptor molecules forming multi-protein complexes that include kinases, transcription factors, and other regulatory molecules. Innate immune signaling cascades induce the expression of genes encoding antimicrobial peptides and other key factors that mount and regulate the immune response against microbial challenge. In this review, we summarize our current understanding of the bacterial and fungal PRRs for homologous innate signaling pathways of insects and mammals in an effort to provide a framework for future studies.

Of flies, mice, and men: evolutionarily conserved tissue damage responses and aging

Studies in flies, mice, and human models have provided a conceptual framework for how paracrine interactions between damaged cells and the surrounding tissue control tissue repair. These studies have amassed evidence for an evolutionarily conserved secretory program that regulates tissue homeostasis. This program coordinates cell survival and proliferation during tissue regeneration and repair in young animals. By virtue of chronic engagement, however, it also contributes to the age-related decline of tissue homeostasis leading to degeneration, metabolic dysfunction, and cancer. Here, we review recent studies that shed light on the nature and regulation of this evolutionarily conserved secretory program.

Paralytic peptide: an insect cytokine that mediates innate immunity

Host animals combat invading pathogens by activating various immune responses. Modulation of the immune pathways by cytokines is critical for efficient pathogen elimination. Insects and mammals possess common innate immune systems, and individual immune pathways have been intensively studied over the last two decades. Relatively less attention, however, has been focused on the functions of cytokines in insect innate immunity. Here, we summarize our recent findings from studies of the insect cytokine, paralytic peptide, in the silkworm Bombyx mori. The content of this report was presented at the First Asian Invertebrate Immunity Symposium. Acute activation of paralytic peptide occurs via proteolysis after stimulation with the cell wall components of pathogens, leading to the induction of a wide range of cellular and humoral immune responses. The pathogenic bacterium Serratia marcescens suppresses paralytic peptide-dependent immune activation, which impairs host resistance. Studies of insect cytokines will broaden our understanding of the basic mechanisms underlying the interaction between host innate immunity and pathogenic agents.