Dachsous and Fat coordinately repress the Dachs-Dlish-Approximated complex to control growth.

Two protocadherins, Dachsous and Fat, regulate organ growth in Drosophila via the Hippo pathway. Dachsous and Fat bind heterotypically to regulate the abundance and subcellular localization of a "core complex" consisting of Dachs, Dlish, and Approximated. This complex localizes to the junctional cortex where it represses Warts. Dachsous is believed to promote growth by recruiting and stabilizing this complex, while Fat represses growth by promoting its degradation. Here, we examine the functional relationships between the intracellular domains of Dachsous and Fat and the core complex. While Dachsous promotes the accumulation of core complex proteins in puncta, it is not required for their assembly. Indeed, the core complex accumulates maximally in the absence of both Dachsous and Fat. Furthermore, Dachsous represses growth in the absence of Fat by removing the core complex from the junctional cortex. Fat similarly recruits core complex components but promotes their degradation. Our findings reveal that Dachsous and Fat coordinately constrain tissue growth by repressing the core complex.

Reduction of endocytosis and EGFR signaling is associated with the switch from isolated to clustered apoptosis during epithelial tissue remodeling in Drosophila.

Epithelial tissues undergo cell turnover both during development and for homeostatic maintenance. Removal of cells is coordinated with the increase in number of newly dividing cells to maintain barrier function of the tissue. In Drosophila metamorphosis, larval epidermal cells (LECs) are replaced by adult precursor cells called histoblasts. Removal of LECs must counterbalance the exponentially increasing adult histoblasts. Previous work showed that the LEC removal accelerates as endocytic activity decreases throughout all LECs. Here, we show that the acceleration is accompanied by a mode switching from isolated single-cell apoptosis to clustered ones induced by the endocytic activity reduction. We identify the epidermal growth factor receptor (EGFR) pathway via extracellular-signal regulated kinase (ERK) activity as the main components downstream of endocytic activity in LECs. The reduced ERK activity, caused by the decrease in endocytic activity, is responsible for the apoptotic mode switching. Initially, ERK is transiently activated in normal LECs surrounding a single apoptotic LEC in a ligand-dependent manner, preventing clustered cell death. Following the reduction of endocytic activity, LEC apoptosis events do not provoke these transient ERK up-regulations, resulting in the acceleration of the cell elimination rate by frequent clustered apoptosis. These findings contrasted with the common perspective that clustered apoptosis is disadvantageous. Instead, switching to clustered apoptosis is required to accommodate the growth of neighboring tissues.

Distinct cellular and junctional dynamics independently regulate the rotation and elongation of the embryonic gut in Drosophila.

Complex organ structures are formed with high reproducibility. To achieve such intricate morphologies, the responsible epithelium undergoes multiple simultaneous shape changes, such as elongation and folding. However, these changes have typically been assessed separately. In this study, we revealed how distinct shape changes are controlled during internal organ morphogenesis. The Drosophila embryonic hindgut undergoes left-right asymmetric rotation and anteroposterior elongation in a tissue-autonomous manner driven by cell sliding and convergent extension, respectively, in the hindgut epithelia. However, the regulation of these processes remains unclear. Through genetic analysis and live imaging, we demonstrated that cell sliding and convergent extension are independently regulated by Myosin1D and E-cadherin, and Par-3, respectively, whereas both require MyosinII activity. Using a mathematical model, we demonstrated that independently regulated cellular dynamics can simultaneously cause shape changes in a single mechanical system using anisotropic edge contraction. Our findings indicate that distinct cellular dynamics sharing a common apparatus can be independently and simultaneously controlled to form complex organ shapes. This suggests that such a mechanism may be a general strategy during complex tissue morphogenesis.

A human DCC variant causing mirror movement disorder reveals that the WAVE regulatory complex mediates axon guidance by netrin-1-DCC.

The axon guidance cue netrin-1 signals through its receptor DCC (deleted in colorectal cancer) to attract commissural axons to the midline. Variants in DCC are frequently associated with congenital mirror movements (CMMs). A CMM-associated variant in the cytoplasmic tail of DCC is located in a conserved motif predicted to bind to a regulator of actin dynamics called the WAVE (Wiskott-Aldrich syndrome protein-family verprolin homologous protein) regulatory complex (WRC). Here, we explored how this variant affects DCC function and may contribute to CMM. We found that a conserved WRC-interacting receptor sequence (WIRS) motif in the cytoplasmic tail of DCC mediated the interaction between DCC and the WRC. This interaction was required for netrin-1-mediated axon guidance in cultured rodent commissural neurons. Furthermore, the WIRS motif of Fra, the Drosophila DCC ortholog, was required for attractive signaling in vivo at the Drosophila midline. The CMM-associated R1343H variant of DCC, which altered the WIRS motif, prevented the DCC-WRC interaction and impaired axon guidance in cultured commissural neurons and in Drosophila. The findings reveal the WRC as a pivotal component of netrin-1-DCC signaling and uncover a molecular mechanism explaining how a human genetic variant in the cytoplasmic tail of DCC may lead to CMM.

miR-210 is essential to retinal homeostasis in fruit flies and mice.

BACKGROUND: miR-210 is one of the most evolutionarily conserved microRNAs. It is known to be involved in several physiological and pathological processes, including response to hypoxia, angiogenesis, cardiovascular diseases and cancer. Recently, new roles of this microRNA are emerging in the context of eye and visual system homeostasis. Recent studies in Drosophila melanogaster unveiled that the absence of miR-210 leads to a progressive retinal degeneration characterized by the accumulation of lipid droplets and disruptions in lipid metabolism. However, the possible conservation of miR-210 knock-out effect in the mammalian retina has yet to be explored. RESULTS: We further investigated lipid anabolism and catabolism in miR-210 knock-out (KO) flies, uncovering significant alterations in gene expression within these pathways. Additionally, we characterized the retinal morphology of flies overexpressing (OE) miR-210, which was not affected by the increased levels of the microRNA. For the first time, we also characterized the retinal morphology of miR-210 KO and OE mice. Similar to flies, miR-210 OE did not affect retinal homeostasis, whereas miR-210 KO mice exhibited photoreceptor degeneration. To explore other potential parallels between miR-210 KO models in flies and mice, we examined lipid metabolism, circadian behaviour, and retinal transcriptome in mice, but found no similarities. Specifically, RNA-seq confirmed the lack of involvement of lipid metabolism in the mice's pathological phenotype, revealing that the differentially expressed genes were predominantly associated with chloride channel activity and extracellular matrix homeostasis. Simultaneously, transcriptome analysis of miR-210 KO fly brains indicated that the observed alterations extend beyond the eye and may be linked to neuronal deficiencies in signal detection and transduction. CONCLUSIONS: We provide the first morphological characterization of the retina of miR-210 KO and OE mice, investigating the role of this microRNA in mammalian retinal physiology and exploring potential parallels with phenotypes observed in fly models. Although the lack of similarities in lipid metabolism, circadian behaviour, and retinal transcriptome in mice suggests divergent mechanisms of retinal degeneration between the two species, transcriptome analysis of miR-210 KO fly brains indicates the potential existence of a shared upstream mechanism contributing to retinal degeneration in both flies and mammals.

CYRI controls epidermal wound closure and cohesion of invasive border cell cluster in Drosophila.

Cell motility is crucial for many biological processes including morphogenesis, wound healing, and cancer invasion. The WAVE regulatory complex (WRC) is a central Arp2/3 regulator driving cell motility downstream of activation by Rac GTPase. CYFIP-related Rac1 interactor (CYRI) proteins are thought to compete with WRC for interaction with Rac1 in a feedback loop regulating lamellipodia dynamics. However, the physiological role of CYRI proteins in vivo in healthy tissues is unclear. Here, we used Drosophila as a model system to study CYRI function at the cellular and organismal levels. We found that CYRI is not only a potent WRC regulator in single macrophages that controls lamellipodial spreading but also identified CYRI as a molecular brake on the Rac-WRC-Arp2/3 pathway to slow down epidermal wound healing. In addition, we found that CYRI limits invasive border cell migration by controlling cluster cohesion and migration. Thus, our data highlight CYRI as an important regulator of cellular and epithelial tissue dynamics conserved across species.

LC-Orbitrap HRMS-Based Proteomics Reveals Novel Mitochondrial Dynamics Regulatory Proteins Associated with RasV12-Induced Glioblastoma (GBM) of Drosophila.

Glioblastoma multiforme (GBM) is the most prevalent and aggressive brain tumor found in adult humans with a poor prognosis and average survival of 14-15 months. In order to have a comprehensive understanding of proteome and identify novel therapeutic targets, this study focused mainly on the differentially abundant proteins (DAPs) of RasV12-induced GBM. RasV12 is a constitutively active Ras mutant form essential for tumor progression by continuously activating signaling pathways leading to uncontrolled tumor growth. This study used a transgenic Drosophila model with RasV12 overexpression using the repo-GAL4 driver line, specifically in glial cells, to study GBM. The high-resolution mass spectrometry (HRMS)-based proteomic analysis of the GBM larval central nervous system identified three novel DAPs specific to mitochondria. These DAPs, probable maleylacetoacetate isomerase 2 (Q9VHD2), bifunctional methylene tetrahydrofolate dehydrogenase (Q04448), and glutamine synthetase1 (P20477), identified through HRMS were further validated by qRT-PCR. The protein-protein interaction analysis revealed interactions between RasV12 and DAPs, with functional links to mitochondrial dynamics regulators such as Drp1, Marf, Parkin, and HtrA2. Notably, altered expressions of Q9VHD2, P20477, and Q04448 were observed during GBM progression, which offers new insights into the involvement of mitochondrial dynamic regulators in RasV12-induced GBM pathophysiology.

Rabex-5 E3 and Rab5 GEF domains differ in their regulation of Ras, Notch, and PI3K signaling in Drosophila wing development.

Rabex-5 (also called RabGEF1), a protein originally characterized for its Rab5 GEF function, also has an A20-like E3 ubiquitin ligase domain. We and others reported that Rabex-5 E3 activity promotes Ras mono- and di-ubiquitination to inhibit Ras signaling in Drosophila and mammals. Subsequently, we reported that Rabex-5 inhibits Notch signaling in the Drosophila hematopoietic system. Here we report genetic interactions using Rabex-5 transgenes encoding domain-specific mutations that show that Rabex-5 requires an intact E3 domain to inhibit Notch signaling in the epithelial tissue of the developing wing. Surprisingly, we discovered that Rabex-5 with an impaired E3 domain but active Rab5 GEF domain suppresses Notch loss-of-function phenotypes and enhances both Notch duplication phenotypes and activated Ras phenotypes consistent with a model that the Rab5 GEF activity of Rabex-5 might positively regulate Ras and Notch. Positive and negative regulation of developmental signaling by its different catalytic domains could allow Rabex-5 to precisely coordinate developmental signaling to fine-tune patterning. Finally, we report that Rabex-5 also inhibits the overgrowth due to loss of PTEN or activation of PI3K but not activation of AKT. Inhibition of Ras, Notch, and PI3K signaling may explain why Rabex-5 is deleted in some cancers. Paradoxically, Rabex-5 is reported to be an oncogene in other cancers. We propose that Rabex-5 acts as a tumor suppressor via its E3 activity to inhibit Ras, Notch, and PI3K signaling and as an oncogene via its Rab5 GEF activity to enhance Ras and Notch signaling.

Dual role for Headcase in hemocyte progenitor fate determination in Drosophila melanogaster.

The hematopoietic organ of the Drosophila larva, the lymph gland, is a simplified representation of mammalian hematopoietic compartments, with the presence of hemocyte progenitors in the medullary zone (MZ), differentiated hemocytes in the cortical zone (CZ), and a hematopoietic niche called the posterior signaling centre (PSC) that orchestrates progenitor differentiation. Our previous work has demonstrated that the imaginal cell factor Headcase (Hdc, Heca) is required in the hematopoietic niche to control the differentiation of hemocyte progenitors. However, the downstream mechanisms of Hdc-mediated hematopoietic control remained unknown. Here we show that Hdc exerts this function by negatively regulating the insulin/mTOR signaling in the niche. When Hdc is depleted in the PSC, the overactivation of this pathway triggers reactive oxygen species (ROS) accumulation and, in turn, the differentiation of effector lamellocytes non-cell-autonomously. Although overactivation of insulin/mTOR signaling normally leads to an increase in the size of the hematopoietic niche, this effect is concealed by cell death caused by hdc loss-of-function. Moreover, we describe here that hdc silencing in progenitors causes cell-autonomous ROS elevation and JNK pathway activation, resulting in decreased MZ size and differentiation of lamellocytes. Similarly to the PSC niche, knocking down hdc in the MZ also leads to caspase activation. Notably, depleting Hdc in the progenitors triggers proliferation, an opposing effect to what is observed in the niche. These findings further our understanding of how progenitor maintenance in the larval lymph gland is controlled autonomously and non-cell-autonomously, and point towards new mechanisms potentially regulating HSC maintenance across vertebrates.

Regional specialization, polyploidy, and seminal fluid transcripts in the Drosophila female reproductive tract.

Sexual reproduction requires the choreographed interaction of female cells and molecules with sperm and seminal fluid. In internally fertilizing animals, these interactions are managed by specialized tissues within the female reproductive tract (FRT), such as a uterus, glands, and sperm storage organs. However, female somatic reproductive tissues remain understudied, hindering insight into the molecular interactions that support fertility. Here, we report the identification, molecular characterization, and analysis of cell types throughout the somatic FRT in the premier Drosophila melanogaster model system. We find that the uterine epithelia is composed of 11 distinct cell types with well-delineated spatial domains, likely corresponding to functionally specialized surfaces that interact with gametes and reproductive fluids. Polyploidy is pervasive: More than half of lower reproductive tract cells are ≥4C. While seminal fluid proteins (SFPs) are typically thought of as male products that are transferred to females, we find that specialized cell types in the sperm storage organs heavily invest in expressing SFP genes. Rates of amino acid divergence between closely related species indicate heterogeneous evolutionary processes acting on male-limited versus female-expressed seminal fluid genes. Together, our results emphasize that more than 40% of annotated seminal fluid genes are better described as shared components of reproductive transcriptomes, which may function cooperatively to support spermatozoa. More broadly, our work provides the molecular foundation for improved technologies to catalyze the functional characterization of the FRT.

Fat body glycolysis defects inhibit mTOR and promote distant muscle disorganization through TNF-α/egr and ImpL2 signaling in Drosophila larvae.

The fat body in Drosophila larvae functions as a reserve tissue and participates in the regulation of organismal growth and homeostasis through its endocrine activity. To better understand its role in growth coordination, we induced fat body atrophy by knocking down several key enzymes of the glycolytic pathway in adipose cells. Our results show that impairing the last steps of glycolysis leads to a drastic drop in adipose cell size and lipid droplet content, and downregulation of the mTOR pathway and REPTOR transcriptional activity. Strikingly, fat body atrophy results in the distant disorganization of body wall muscles and the release of muscle-specific proteins in the hemolymph. Furthermore, we showed that REPTOR activity is required for fat body atrophy downstream of glycolysis inhibition, and that the effect of fat body atrophy on muscles depends on the production of TNF-α/egr and of the insulin pathway inhibitor ImpL2.

A highly conserved A-to-I RNA editing event within the glutamate-gated chloride channel GluClα is necessary for olfactory-based behaviors in Drosophila.

A-to-I RNA editing is a cellular mechanism that generates transcriptomic and proteomic diversity, which is essential for neuronal and immune functions. It involves the conversion of specific adenosines in RNA molecules to inosines, which are recognized as guanosines by cellular machinery. Despite the vast number of editing sites observed across the animal kingdom, pinpointing critical sites and understanding their in vivo functions remains challenging. Here, we study the function of an evolutionary conserved editing site in Drosophila, located in glutamate-gated chloride channel (GluClα). Our findings reveal that flies lacking editing at this site exhibit reduced olfactory responses to odors and impaired pheromone-dependent social interactions. Moreover, we demonstrate that editing of this site is crucial for the proper processing of olfactory information in projection neurons. Our results highlight the value of using evolutionary conservation as a criterion for identifying editing events with potential functional significance and paves the way for elucidating the intricate link between RNA modification, neuronal physiology, and behavior.

Blockade of Crk eliminates Yki/YAP-activated tumors via JNK-mediated apoptosis in Drosophila.

Selective elimination of cancer cells without causing deleterious effects on normal cells is an ideal anti-cancer strategy. Here, using Drosophila cancer model, we performed an in vivo RNAi screen for anti-cancer targets that selectively eliminate tumors without affecting normal tissue growth. In Drosophila imaginal epithelium, clones of cells expressing oncogenic Ras with simultaneous mutations in the cell polarity gene scribble (RasV12/scrib-/-) develop into malignant tumors. We found that knockdown of Crk, the Drosophila ortholog of human CRK (CT10 regulatory kinase) and CRKL (Crk-like) adapter proteins, significantly suppresses growth of RasV12/scrib-/- tumors by inducing c-Jun N-terminal kinase (JNK)-mediated apoptosis, while it does not affect growth of normal epithelium. Mechanistically, Crk inhibition blocks Yorkie (Yki)/YAP activity by impairing F-actin accumulation, an upstream event of Yki/YAP activation in tumors. Inhibition of Yki/YAP in tumors causes intracellular JNK signaling to be used for apoptosis induction. Given that molecules and signaling pathways identified in Drosophila are highly conserved and activated in human cancers, our findings would provide a novel, to the best of our knowledge, anti-cancer strategy against YAP-activated cancers.

Bcl-2 Orthologues, Buffy and Debcl, Can Suppress Drp1-Dependent Age-Related Phenotypes in Drosophila.

The relationship of Amyotrophic Lateral Sclerosis, Parkinson's disease, and other age-related neurodegenerative diseases with mitochondrial dysfunction has led to our study of the mitochondrial fission gene Drp1 in Drosophila melanogaster and aspects of aging. Previously, the Drp1 protein has been demonstrated to interact with the Drosophila Bcl-2 mitochondrial proteins, and Drp1 mutations can lead to mitochondrial dysfunction and neuronal loss. In this study, the Dopa decarboxylase-Gal4 (Ddc-Gal4) transgene was exploited to direct the expression of Drp1 and Drp1-RNAi transgenes in select neurons. Here, the knockdown of Drp1 seems to compromise locomotor function throughout life but does not alter longevity. The co-expression of Buffy suppresses the poor climbing induced by the knockdown of the Drp1 function. The consequences of Drp1 overexpression, which specifically reduced median lifespan and diminished climbing abilities over time, can be suppressed through the directed co-overexpression of pro-survival Bcl-2 gene Buffy or by the co-knockdown of the pro-cell death Bcl-2 homologue Debcl. Alteration of the expression of Drp1 acts to phenocopy neurodegenerative disease phenotypes in Drosophila, while overexpression of Buffy can counteract or rescue these phenotypes to improve overall health. The diminished healthy aging due to either the overexpression of Drp1 or the RNA interference of Drp1 has produced novel Drosophila models for investigating mechanisms underlying neurodegenerative disease.

Linkage of alternative exon assembly in Drosophila TrpA1 transcripts.

Drosophila TrpA1 (transient receptor potential ankyrin 1) transcripts are alternatively spliced at 2 distinct sites each with a choice of mutually exclusive exons. The first site determines exon1 encoding the amino terminus to produce either nucleophile-, electrophile- and noxious temperature-gated TRPA1(A) or electrophile- and innocuous warmth-gated TRPA1(B). The second site selects for exon10, resulting in TrpA1 variants with either exon10a or exon10b encoding a domain between the N-terminal ankyrin repeats and the transmembrane segments. Although unbiased assembly would generate TRPA1 with 4 different domain combinations, the functional impact of these alternative domains remains to be thoroughly examined. Here, we find that there is a relatively strong linkage in mRNA splicing between the 2 sites in the case of TrpA1(B), but not TrpA1(A), transcripts. Our semiquantitative assay, consisting of reverse transcription polymerase chain reaction and Sanger sequencing, revealed that exon10b is little coupled with TrpA1(B) transcripts, suggesting that only 3 isoforms, TRPA1(A)-exon10a [denoted as TRPA1(A)], TRPA1(A)-exon10b [TRPA1(A)10b], and TRPA1(B)-exon10a [TRPA1(B)], are present at detectable levels using our method. Interestingly, heterologously expressed TRPA1(A)10b showed elevated sensitivity to low concentrations of N-methyl maleimide, a cysteine-modifying electrophile, compared with other isoforms. Equivalent isoforms in malaria-transmitting Anopheles gambiae displayed a similar pattern of isoform-dependent N-methyl maleimide dose dependences, suggesting that the chemosensory regulation by selective domain assembly is conserved in insect TRPA1s. Thus, alternative RNA splicing of exon10 is coordinated in conjunction with the first exons, regulating chemical sensitivity of insect TRPA1s.

An unscheduled switch to endocycles induces a reversible senescent arrest that impairs growth of the Drosophila wing disc.

A programmed developmental switch to G / S endocycles results in tissue growth through an increase in cell size. Unscheduled, induced endocycling cells (iECs) promote wound healing but also contribute to cancer. Much remains unknown, however, about how these iECs affect tissue growth. Using the D. melanogaster wing disc as model, we find that populations of iECs initially increase in size but then subsequently undergo a heterogenous arrest that causes severe tissue undergrowth. iECs acquired DNA damage and activated a Jun N-terminal kinase (JNK) pathway, but, unlike other stressed cells, were apoptosis-resistant and not eliminated from the epithelium. Instead, iECs entered a JNK-dependent and reversible senescent-like arrest. Senescent iECs promoted division of diploid neighbors, but this compensatory proliferation did not rescue tissue growth. Our study has uncovered unique attributes of iECs and their effects on tissue growth that have important implications for understanding their roles in wound healing and cancer.

OVO positively regulates essential maternal pathways by binding near the transcriptional start sites in the Drosophila female germline.

Differentiation of female germline stem cells into a mature oocyte includes the expression of RNAs and proteins that drive early embryonic development in Drosophila. We have little insight into what activates the expression of these maternal factors. One candidate is the zinc-finger protein OVO. OVO is required for female germline viability and has been shown to positively regulate its own expression, as well as a downstream target, ovarian tumor, by binding to the transcriptional start site (TSS). To find additional OVO targets in the female germline and further elucidate OVO's role in oocyte development, we performed ChIP-seq to determine genome-wide OVO occupancy, as well as RNA-seq comparing hypomorphic and wild type rescue ovo alleles. OVO preferentially binds in close proximity to target TSSs genome-wide, is associated with open chromatin, transcriptionally active histone marks, and OVO-dependent expression. Motif enrichment analysis on OVO ChIP peaks identified a 5'-TAACNGT-3' OVO DNA binding motif spatially enriched near TSSs. However, the OVO DNA binding motif does not exhibit precise motif spacing relative to the TSS characteristic of RNA polymerase II complex binding core promoter elements. Integrated genomics analysis showed that 525 genes that are bound and increase in expression downstream of OVO are known to be essential maternally expressed genes. These include genes involved in anterior/posterior/germ plasm specification (bcd, exu, swa, osk, nos, aub, pgc, gcl), egg activation (png, plu, gnu, wisp, C(3)g, mtrm), translational regulation (cup, orb, bru1, me31B), and vitelline membrane formation (fs(1)N, fs(1)M3, clos). This suggests that OVO is a master transcriptional regulator of oocyte development and is responsible for the expression of structural components of the egg as well as maternally provided RNAs that are required for early embryonic development.

Glial ferritin maintains neural stem cells via transporting iron required for self-renewal in Drosophila.

Stem cell niche is critical for regulating the behavior of stem cells. Drosophila neural stem cells (Neuroblasts, NBs) are encased by glial niche cells closely, but it still remains unclear whether glial niche cells can regulate the self-renewal and differentiation of NBs. Here, we show that ferritin produced by glia, cooperates with Zip13 to transport iron into NBs for the energy production, which is essential to the self-renewal and proliferation of NBs. The knockdown of glial ferritin encoding genes causes energy shortage in NBs via downregulating aconitase activity and NAD+ level, which leads to the low proliferation and premature differentiation of NBs mediated by Prospero entering nuclei. More importantly, ferritin is a potential target for tumor suppression. In addition, the level of glial ferritin production is affected by the status of NBs, establishing a bicellular iron homeostasis. In this study, we demonstrate that glial cells are indispensable to maintain the self-renewal of NBs, unveiling a novel role of the NB glial niche during brain development.

Iron is an essential nutrient for almost all living organisms. For example, iron contributes to the replication of DNA, the generation of energy inside cells, and the transport of oxygen around the body. Iron deficiency is the most common of all nutrient deficiencies, affecting over 40% of children worldwide. This can lead to anemia and also impair how the brain and nervous system develop, potentially resulting in long-lasting cognitive damage, even after the deficiency has been treated. It is poorly understood how iron contributes to the development of the brain and nervous system. In particular, whether and how it supports nerve stem cells (or NSCs for short) which give rise to the various neural types in the mature brain. To investigate, Ma et al. experimentally reduced the levels of ferritin (a protein which stores iron) in the developing brains of fruit fly larvae. This reduction in ferritin led to lower numbers of NSCs and a smaller brain. Unexpectedly, this effect was largest when ferritin levels were reduced in glial cells which support and send signals to NSCs, rather than in the stem cells themselves. Ma et al. then used fluorescence microscopy to confirm that glial cells make and contain a lot of ferritin which can be transported to NSCs. Adding iron supplements to the diet of flies lacking ferritin did not lead to normal numbers of stem cells in the brains of the developing fruit flies, whereas adding compounds that reduce the amount of iron led to lower numbers of stem cells. Together, this suggests that ferritin transports iron from glial cells to the NSCs. Without ferritin and iron, the NSCs could not produce enough energy to divide and make new stem cells. This caused the NSCs to lose the characteristics of stem cells and prematurely turn into other types of neurons or glial cells. Together, these findings show that when iron cannot move from glial cells to NSCs this leads to defects in brain development. Future experiments will have to test whether a similar transport of iron from supporting cells to NSCs also occurs in the developing brains of mammals, and whether this mechanism applies to stem cells in other parts of the body.

High sugar diet promotes tumor progression paradoxically through aberrant upregulation of pepck1.

High dietary sugar (HDS), a contemporary dietary concern due to excessive intake of added sugars and carbohydrates, escalates the risk of metabolic disorders and concomitant cancers. However, the molecular mechanisms underlying HDS-induced cancer progression are not completely understood. We found that phosphoenolpyruvate carboxykinase 1 (PEPCK1), a pivotal enzyme in gluconeogenesis, is paradoxically upregulated in tumors by HDS, but not by normal dietary sugar (NDS), during tumor progression. Targeted knockdown of pepck1, but not pepck2, specifically in tumor tissue in Drosophila in vivo, not only attenuates HDS-induced tumor growth but also significantly improves the survival of Ras/Src tumor-bearing animals fed HDS. Interestingly, HP1a-mediated heterochromatin interacts directly with the pepck1 gene and downregulates pepck1 gene expression in wild-type Drosophila. Mechanistically, we demonstrated that, under HDS conditions, pepck1 knockdown reduces both wingless and TOR signaling, decreases evasion of apoptosis, reduces genome instability, and suppresses glucose uptake and trehalose levels in tumor cells in vivo. Moreover, rational pharmacological inhibition of PEPCK1, using hydrazinium sulfate, greatly improves the survival of tumor-bearing animals with pepck1 knockdown under HDS. This study is the first to show that elevated levels of dietary sugar induce aberrant upregulation of PEPCK1, which promotes tumor progression through altered cell signaling, evasion of apoptosis, genome instability, and reprogramming of carbohydrate metabolism. These findings contribute to our understanding of the complex relationship between diet and cancer at the molecular, cellular, and organismal levels and reveal PEPCK1 as a potential target for the prevention and treatment of cancers associated with metabolic disorders.

The JNK and Hippo pathways control epithelial integrity and prevent tumor initiation by regulating an overlapping transcriptome.

Epithelial organs maintain their integrity and prevent tumor initiation by actively removing defective cells, such as those that have lost apicobasal polarity. Here, we identify how transcription factors of two key signaling pathways-Jun-N-terminal kinase (JNK) and Hippo-regulate epithelial integrity by controlling transcription of an overlapping set of target genes. Targeted DamID experiments reveal that, in proliferating cells of the Drosophila melanogaster eye, the AP-1 transcription factor Jun and the Hippo pathway transcription regulators Yorkie and Scalloped bind to a common suite of target genes that promote organ growth. In defective neoplastic cells, AP-1 transcription factors repress transcription of growth genes together with the C-terminal binding protein (CtBP) co-repressor. If gene repression by AP-1/CtBP fails, neoplastic tumor growth ensues, driven by Yorkie/Scalloped. Thus, AP-1/CtBP eliminates defective cells and prevents tumor initiation by acting in parallel to Yorkie/Scalloped to repress expression of a shared transcriptome. These findings shed new light on the maintenance of epithelial integrity and tumor suppression.