Complexities in the role of acetylation dynamics in modifying inducible gene activation parameters.

High levels of histone acetylation are associated with the regulatory elements of active genes, suggesting a link between acetylation and gene activation. We revisited this model, in the context of EGF-inducible gene expression and found that rather than a simple unifying model, there are two broad classes of genes; one in which high lysine acetylation activity is required for efficient gene activation, and a second group where the opposite occurs and high acetylation activity is inhibitory. We examined the latter class in more detail using EGR2 as a model gene and found that lysine acetylation levels are critical for several activation parameters, including the timing of expression onset, and overall amplitudes of the transcriptional response. In contrast, DUSP1 responds in the canonical manner and its transcriptional activity is promoted by acetylation. Single cell approaches demonstrate heterogenous activation kinetics of a given gene in response to EGF stimulation. Acetylation levels modify these heterogenous patterns and influence both allele activation frequencies and overall expression profile parameters. Our data therefore point to a complex interplay between acetylation equilibria and target gene induction where acetylation level thresholds are an important determinant of transcriptional induction dynamics that are sensed in a gene-specific manner.

Growth Hormone Modulation of Hepatic Epidermal Growth Factor Receptor Signaling.

Epidermal growth factor receptor (EGFR) signaling has a central role in the regenerative response of the liver upon injury and is involved in cellular transformation linked to chronic damage. Hepatic EGFR expression, trafficking, and signaling are regulated by growth hormone (GH). Chronically elevated GH levels are associated with liver cancer development and progression in mice. Studies in different in vivo experimental models indicate that EGF and GH mutually crossregulate in a complex manner. Several factors, such as the extent of exposure to supraphysiological GH levels and the pattern of GH administration, are important variables to be considered in exploring the interplay between the two hormones in connection with the progression of hepatic tumors.

Epidermal growth factor alleviates the negative impact of urea on frozen-thawed bovine sperm, but the subsequent developmental competence is compromised.

Upon insemination, sperm cells are exposed to components of the female reproductive tract (FRT) fluids, such as urea and epidermal growth factor (EGF). It has been shown that both urea and EGF use EGF receptor signaling and produce reactive oxygen species (ROS) that are required at certain levels for sperm capacitation and acrosome reaction. We therefore hypothesized that during bovine sperm capacitation, a high level of urea and EGF could interfere with sperm function through overproduction of ROS. High-level urea (40 mg/dl urea is equal to 18.8 mg/dl of blood urea nitrogen) significantly increased ROS production and TUNEL-positive sperm (sperm DNA fragmentation, sDF) percentage, but decreased HOS test score, progressive motility, acrosome reaction and capacitation. The EGF reversed the negative effects of urea on all sperm parameters, with the exception of ROS production and DNA fragmentation, which were higher in urea-EGF-incubated sperm than in control-sperm. The developmental competence of oocytes inseminated with urea-EGF-incubated sperm was significantly reduced compared to the control. A close association of ROS production or sDF with 0-pronuclear and sperm non-capacitation rates was found in the network analysis. In conclusion, EGF enhanced urea-reduced sperm motility; however, it failed to reduce urea-increased sperm ROS or sDF levels and to enhance subsequent oocyte competence. The data suggests that any study to improve sperm quality should be followed by a follow-up assessment of the fertilization outcome.

Epidermal growth factor and three-dimensional scaffolds provide conducive environment for differentiation of mouse embryonic stem cells into oocyte-like cells.

Three-dimensional (3D) culture provides a biomimicry of the naive microenvironment that can support cell proliferation, differentiation, and regeneration. Some growth factors, such as epidermal growth factor (EGF), facilitate normal meiosis during oocyte maturation in vivo. In this study, a scaffold-based 3D coculture system using purified alginate was applied to induce oocyte differentiation from mouse embryonic stem cells (mESCs). mESCs were induced to differentiate into oocyte-like cells using embryoid body protocol in the two-dimensional or 3D microenvironment in vitro. To increase the efficiency of the oocyte-like cell differentiation from mESCs, we employed a coculture system using ovarian granulosa cells in the presence or absence of epidermal growth factor (+EGF or -EGF) for 14 days and then the cells were assessed for germ cell differentiation, meiotic progression, and oocyte maturation markers. The cultures exposed to EGF in the alginate-based 3D microenvironment showed the highest level of premeiotic (Oct4 and Mvh), meiotic (Scp1, Scp3, Stra8, and Rec8), and oocyte maturation (Gdf9, Cx37, and Zp2) marker genes (p < .05) in comparison to other groups. According to the gene-expression patterns, we can conclude that alginate-based 3D coculture system provided a highly efficient protocol for oocyte-like cell differentiation from mESCs. The data showed that this culture system along with EGF improved the rate of in vitro oocyte-like cell differentiation.

TGFß and EGF signaling orchestrates the AP-1- and p63 transcriptional regulation of breast cancer invasiveness.

Activator protein (AP)-1 transcription factors are essential elements of the pro-oncogenic functions of transforming growth factor-ß (TGFß)-SMAD signaling. Here we show that in multiple HER2+ and/or EGFR+ breast cancer cell lines these AP-1-dependent tumorigenic properties of TGFß critically rely on epidermal growth factor receptor (EGFR) activation and expression of the ΔN isoform of transcriptional regulator p63. EGFR and ΔNp63 enabled and/or potentiated the activation of a subset of TGFß-inducible invasion/migration-associated genes, e.g., ITGA2, LAMB3, and WNT7A/B, and enhanced the recruitment of SMAD2/3 to these genes. The TGFß- and EGF-induced binding of SMAD2/3 and JUNB to these gene loci was accompanied by p63-SMAD2/3 and p63-JUNB complex formation. p63 and EGFR were also found to strongly potentiate TGFß induction of AP-1 proteins and, in particular, FOS family members. Ectopic overexpression of FOS could counteract the decrease in TGFß-induced gene activation after p63 depletion. p63 is also involved in the transcriptional regulation of heparin binding (HB)-EGF and EGFR genes, thereby establishing a self-amplification loop that facilitates and empowers the pro-invasive functions of TGFß. These cooperative pro-oncogenic functions of EGFR, AP-1, p63, and TGFß were efficiently inhibited by clinically relevant chemical inhibitors. Our findings may, therefore, be of importance for therapy of patients with breast cancers with an activated EGFR-RAS-RAF pathway.

Disruption of EGF Feedback by Intestinal Tumors and Neighboring Cells in Drosophila.

In healthy adult organs, robust feedback mechanisms control cell turnover to enforce homeostatic equilibrium between cell division and death [1, 2]. Nascent tumors must subvert these mechanisms to achieve cancerous overgrowth [3-7]. Elucidating the nature of this subversion can reveal how cancers become established and may suggest strategies to prevent tumor progression. In adult Drosophila intestine, a well-studied model of homeostatic cell turnover, the linchpin of cell equilibrium is feedback control of the epidermal growth factor (EGF) protease Rhomboid (Rho). Expression of Rho in apoptotic cells enables them to secrete EGFs, which stimulate nearby stem cells to undergo replacement divisions [8]. As in mammals, loss of adenomatous polyposis coli (APC) causes Drosophila intestinal stem cells to form adenomas [9]. Here, we demonstrate that Drosophila APC-/- tumors trigger widespread Rho expression in non-apoptotic cells, resulting in chronic EGF signaling. Initially, nascent APC-/- tumors induce rho in neighboring wild-type cells via acute, non-autonomous activation of Jun N-terminal kinase (JNK). During later growth and multilayering, APC-/- tumors induce rho in tumor cells by autonomous downregulation of E-cadherin (E-cad) and consequent activity of p120-catenin. This sequential dysregulation of tumor non-autonomous and -autonomous EGF signaling converts tissue-level feedback into feed-forward activation that drives cancerous overgrowth. Because Rho, EGF receptor (EGFR), and E-cad are associated with colorectal cancer in humans [10-17], our findings may shed light on how human colorectal tumors progress.

Regulatory cytokines prescribe the outcome of the inflammation in the process of pseudoexfoliation production.

BACKGROUND: The purpose of this study is to reveal the participation of different regulatory cytokines within the process of pseudoexfoliation (PEX). METHODS: Our study included 140 patients referred to cataract surgery with early and late stage of pseudoexfoliation syndrome (XFS) or pseudoexfoliation glaucoma (XFG). Humor and serum levels of cytokines: transforming growth factor beta (TGF-ß), platelet-derived growth factor (PDGF), epidermal growth factor (EGF), insulin-like growth factor (IGF), IL-8 and interferon-inducible T cell alpha chemoattractant (ITAC) were measured in a sample using high sensitivity enzyme-linked immunoabsorbent assay (ELISA) kit. RESULTS: Our results indicate that profibrotic action induced by increasing TGF-ß and PDGF locally activates fibrous tissue production in the early XFS with a prolonged effect of PDGF (late XFS) and finally (XFG stage) it is dominantly controlled by EGF and IGF. ITAC overrides angiogenetic effects of IL-8 in XFG. CONCLUSION: Based on our findings, local chronic inflammation in the eye is accompanied by the secretion of different profibrotic cytokines (TGF-ß, PDGF, EGF, IGF, IL-8) without angiogenesis due to effects of ITAC.

Generating an Artificial Intestine for the Treatment of Short Bowel Syndrome.

Intestinal failure is defined as the inability to maintain fluid, nutrition, energy, and micronutrient balance that leads to the inability to gain or maintain weight, resulting in malnutrition and dehydration. Causes of intestinal failure include short bowel syndrome (ie, the physical loss of intestinal surface area and severe intestinal dysmotility). For patients with intestinal failure who fail to achieve enteral autonomy through intestinal rehabilitation programs, the current treatment options are expensive and associated with severe complications. Therefore, the need persists for next-generation therapies, including cell-based therapy, to increase intestinal regeneration, and development of the tissue-engineered small intestine.

EGF suppresses the expression of miR-124a in pancreatic ß cell lines via ETS2 activation through the MEK and PI3K signaling pathways.

Diabetes mellitus is characterized by pancreatic ß cell dysfunction. Previous studies have indicated that epidermal growth factor (EGF) and microRNA-124a (miR-124a) play opposite roles in insulin biosynthesis and secretion by beta cells. However, the underlying mechanisms remain poorly understood. In the present study, we demonstrated that EGF could inhibit miR-124a expression in beta cell lines through downstream signaling pathways, including mitogen-activated protein kinase kinase (MEK) and phosphatidylinositol 3-kinase (PI3K) cascades. Further, the transcription factor ETS2, a member of the ETS (E26 transformation-specific) family, was identified to be responsible for the EGF-mediated suppression of miR-124a expression, which was dependent on ETS2 phosphorylation at threonine 72. Activation of ETS2 decreased miR-124a promoter transcriptional activity through the putative conserved binding sites AGGAANA/TN in three miR-124a promoters located in different chromosomes. Of note, ETS2 played a positive role in regulating beta cell function-related genes, including miR-124a targets, Forkhead box a2 (FOXA2) and Neurogenic differentiation 1 (NEUROD1), which may have partly been through the inhibition of miR-124 expression. Knockdown and overexpression of ETS2 led to the prevention and promotion of insulin biosynthesis respectively, while barely affecting the secretion ability. These results suggest that EGF may induce the activation of ETS2 to inhibit miR-124a expression to maintain proper beta cell functions and that ETS2, as a novel regulator of insulin production, is a potential therapeutic target for diabetes mellitus treatment.

MUC13 promotes the development of colitis-associated colorectal tumors via ß-catenin activity.

Many adenocarcinomas, including colorectal cancer (CRC), overexpress the MUC13 cell surface mucin, but the functional significance and mechanisms are unknown. Here, we report the roles of MUC13 in colonic tumorigenesis and tumor progression. High-MUC13 expression is associated with poor survival in two independent patient cohorts. In a comprehensive series of in vivo experiments, we identified a critical role for MUC13 in the development of this malignancy, by promoting survival and proliferation of tumor-initiating cells and driving an immunosuppressive environment that protects tumors from checkpoint inhibitor immunotherapy. In Muc13-deficient mice, fewer tumors are generated after exposure to carcinogens and inflammation, they have markedly reduced ß-catenin signaling, have more tumor-infiltrating CD103+ dendritic cells and CD8+ T lymphocytes, fewer myeloid-derived suppressor cells, and are rendered sensitive to checkpoint inhibitor immunotherapy (anti-PD-L1). Mechanistically, we show that MUC13 protects ß-catenin from degradation, by interacting with GSK-3ß, which increases ß-catenin nuclear translocation and promotes its signaling, thereby driving cancer initiation, progression, invasion, and immune suppression. Therefore, MUC13 is a potential marker of poor prognosis in colorectal cancer, and inhibiting MUC13 may be useful in the treatment of colitis-associated cancer and sensitizing tumors to immunotherapy.

[The role of EGF-like factor signaling pathway in granulosa cells in regulation of oocyte maturation and development].

The surge of luteinizing hormone (LH) in preovulatory ovarian follicles triggers the resumption of meiosis in oocytes and induces the proliferation of surrounding cumulus granulosa cells. It is believed that LH receptors are expressed in the mural granulosa cells, but not the oocytes and the surrounding cumulus cells, suggesting that the LH signaling is mediated by factors produced by the granulosa cells. However, the mechanism underlying oocyte maturation induced by LH before ovulation has been controversial. Current studies suggest that LH binds on to its receptor on granulosa cells of the follicular wall to promote the production of EGF-like factors, which activate various signaling cascades and induce oocyte maturation and development. Since the in vitro maturation system is difficult to simulate the in vivo physiological environment, in vitro cultured follicles are likely to be de?cient in the EGF-like factors, which could result in the poor developmental competency of in vitro cultured oocytes and restrict their efficient utilization. In this review, we summarize the EGF-like factor signaling system in granulosa cells and its regulation of oocyte maturation and development. It aims to optimize the in vitro maturation culture system of oocytes and increase the EGF-like factor signaling system in cumulus granulosa cells, thereby providing a framework for improving the efficiency on in vitro maturation of oocytes.

EGF promotes HIF-1α expression in colorectal cancer cells and tumor metastasis by regulating phosphorylation of STAT3.

OBJECTIVE: Hypoxia-inducible factor 1α (HIF-1α) functions importantly in the development of colorectal cancer. HIF-1α is induced by some cytokines and growth factors and is also regulated by another kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathways. Meanwhile, inhibiting HIF-1α expression can inhibit the development of colorectal cancer. The aim of this study was to explore the effect of epidermal growth factor (EGF) on the activation of signal transducer and activator of transcription 3 (STAT3) in human colorectal cancer cells SW480. In addition, the underlying mechanism of the STAT3 signaling pathway in regulating HIF-1α and further affecting tumorigenesis and metastasis was investigated. MATERIALS AND METHODS: Immunofluorescence and Western blotting were used to detect the activation of STAT3 by EGF in human colorectal cancer cells SW480. SW480 cells were transfected with STAT3 siRNA or treated with STAT3 inhibitor Niclosamide, and then stimulated with EGF to change the expressions of STAT3 and p-STAT3. The expression level of HIF-1α mRNA in SW480 cells was detected by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR). In addition, transwell assay and tumor formation experiments were performed to validate whether STAT3 and HIF-1α affected SW480 through EGF. RESULTS: STAT3 was not activated in SW480 cells in vitro. EGF induced STAT3 activation and enhanced its phosphorylation level, so that it shuttled into the nucleus. Phosphorylated activation of STAT3 was a necessary condition for EGF to induce HIF-1α up-regulation. Both HIF-1α and EGF-induced phosphorylation of STAT3 could significantly promote the proliferation and metastasis of SW480, and enhance tumorigenesis. CONCLUSIONS: In SW480 cells, EGF regulated HIF-1α through the STAT3 phosphorylation pathway, eventually promoting the occurrence and metastasis of colorectal cancer.

Epidermal Growth Factor - based adhesion substrates elicit myoblast scattering, proliferation, differentiation and promote satellite cell myogenic activation.

The biochemical properties of muscle extracellular matrix are essential for stem cell adhesion, motility, proliferation and myogenic development. Recombinant elastin-like polypeptides are synthetic polypeptides that, besides maintaining some properties of the native protein, can be tailored by fusing bioactive sequences to their C-terminal. Our laboratory synthesized several Human Elastin-Like Polypeptides (HELP) derived from the sequence of human tropoelastin. Here, we developed a novel HELP family member by fusing the elastin-like backbone to the sequence of human Epidermal Growth Factor. We employed this synthetic protein, named HEGF, either alone or in combination with other proteins of the HELP family carrying RGD-integrin binding sites, as adhesion substrate for C2C12 myoblasts and satellite cells primary cultures. Adhesion of myoblasts to HEGF-based substrates induced scattering, decreased adhesion and cytoskeleton assembly; the concomitant presence of the RGD motifs potentiated all these effects. Recombinant substrates induced myoblasts proliferation, differentiation and the development of multinucleated myotubes, thus favoring myoblasts expansion and preserving their myogenic potential. The effects induced by adhesion substrates were inhibited by AG82 (Tyrphostin 25) and herbimycin A, indicating their dependence on the activation of both the EGF receptor and the tyrosine kinase c-src. Finally, HEGF increased the number of muscle stem cells (satellite cells) derived from isolated muscle fibers in culture, thus highlighting its potential as a novel substrate for skeletal muscle regeneration strategies.

ß-Heregulin impairs EGF induced PLC-γ1 signalling in human breast cancer cells.

The interplay of ErbB receptor homo- and heterodimers plays a crucial role in the pathology of breast cancer since activated signal transduction cascades coordinate proliferation, survival and migration of cells. EGF and ß-Heregulin are well characterised ligands known to induce ErbB homo- and heterodimerisation, which have been associated with disease progression. In the present study, we investigated the impact of both factors on the migration of MDA-NEO and MDA-HER2 human breast cancer cells. MDA-NEO cells are positive for EGFR and HER3, while MDA-HER2 cells express EGFR, HER2 and HER3. Cell migration analysis revealed that ß-Heregulin potently impaired EGF induced migration in both cell lines. Western blot studies showed that both ErbB receptor and PLC-γ1 tyrosine phosphorylation levels were diminished in EGF and ß-Heregulin co-treated MDA-NEO and MDA-HER2 cells, which was further correlated to a significantly impaired calcium influx. Our data indicate that EGF and HRG may interfere with each other for receptor binding and dimerisation, which ultimately has an impact on signalling outcome.

Effect of Optimized Concentrations of Basic Fibroblast Growth Factor and Epidermal Growth Factor on Proliferation of Fibroblasts and Expression of Collagen: Related to Pelvic Floor Tissue Regeneration.

BACKGROUND: Fibroblasts were the main seed cells in the studies of tissue engineering of the pelvic floor ligament. Basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) were widely studied but at various concentrations. This study aimed to optimize the concentrations of combined bFGF and EGF by evaluating their effects on proliferation and collagen secretion of fibroblasts. METHODS: Fibroblasts were differentiated from rat adipose mesenchymal stem cells (ADSCs). Flow cytometry and immunohistochemistry were used for cell identification. The growth factors were applied at concentrations of 0, 1, 10, and 100 ng/ml as three groups: (1) bFGF alone, (2) EGF alone, and (3) bFGF mixed with EGF. Cell proliferation was evaluated by Cell Counting Kit-8 assays. Expression of Type I and III collagen (Col-I and Col-III) mRNAs was evaluated by real-time quantitative reverse transcription-polymerase chain reaction. Statistical analysis was performed with SPSS software and GraphPad Prism using one-way analysis of variance and multiple t-test. RESULTS: ADSCs were successfully isolated from rat adipose tissue as identified by expression of typical surface markers CD29, CD44, CD90, and CD45 in flow cytometry. Fibroblasts induced from ADSC, compared with ADSCs, were with higher mRNA expression levels of Col I and Col III (F = 1.29, P = 0.0390). bFGF, EGF, and the mixture of bFGF with EGF can enhanced fibroblasts proliferation, and the concentration of 10 ng/ml of the mixture of bFGF with EGF displayed most effectively (all P < 0.05). The expression levels of Col-I and Col-III mRNAs in fibroblasts displayed significant increases in the 10 ng/ml bFGF combined with EGF group (all P < 0.05). CONCLUSIONS: The optimal concentration of both bFGF and EGF to promote cell proliferation and collagen expression in fibroblasts was 10 ng/ml at which fibroblasts grew faster and secreted more Type I and III collagens into the extracellular matrix, which might contribute to the stability of the pelvic floor microenvironment.

Merlin/ERM proteins regulate growth factor-induced macropinocytosis and receptor recycling by organizing the plasma membrane:cytoskeleton interface.

The architectural and biochemical features of the plasma membrane are governed by its intimate association with the underlying cortical cytoskeleton. The neurofibromatosis type 2 (NF2) tumor suppressor merlin and closely related membrane:cytoskeleton-linking protein ezrin organize the membrane:cytoskeleton interface, a critical cellular compartment that both regulates and is regulated by growth factor receptors. An example of this poorly understood interrelationship is macropinocytosis, an ancient process of nutrient uptake and membrane remodeling that can both be triggered by growth factors and manage receptor availability. We show that merlin deficiency primes the membrane:cytoskeleton interface for epidermal growth factor (EGF)-induced macropinocytosis via a mechanism involving increased cortical ezrin, altered actomyosin, and stabilized cholesterol-rich membranes. These changes profoundly alter EGF receptor (EGFR) trafficking in merlin-deficient cells, favoring increased membrane levels of its heterodimerization partner, ErbB2; clathrin-independent internalization; and recycling. Our work suggests that, unlike Ras transformed cells, merlin-deficient cells do not depend on macropinocytic protein scavenging and instead exploit macropinocytosis for receptor recycling. Finally, we provide evidence that the macropinocytic proficiency of NF2-deficient cells can be used for therapeutic uptake. This work provides new insight into fundamental mechanisms of macropinocytic uptake and processing and suggests new ways to interfere with or exploit macropinocytosis in NF2 mutant and other tumors.

EGF-Mediated Overexpression of Myc Attenuates miR-26b by Recruiting HDAC3 to Induce Epithelial-Mesenchymal Transition of Lens Epithelial Cells.

The previous study has demonstrated that epidermal growth factor (EGF) and EGF receptor (EGFR) signaling plays a critical role in the development of posterior capsule opacification (PCO) through regulating lens epithelial cells (LECs) proliferation. Recent studies have suggested that the residual LECs undergo proliferation and migration, and epithelial-mesenchymal transition (EMT) is the important cause of PCO formation after cataract surgery. EMT of LECs is considered to be playing a central role in the pathogenesis of PCO. In the present study, we investigated whether and how EGF may regulate EMT of LECs. First, we demonstrated that EGF and EGFR signaling induces Myc overexpression in primary human lens epithelial cells (HLECs). In turn, Myc overexpression could inhibit miR-26b by recruitment of HDAC3. Consequently, the downregulated expression of miR-26b increased the expression of EZH2 in primary HLECs. Mechanistically, miR-26b directly controls EZH2 expression by targeting its 3'-UTR in HLECs by luciferase reporter assays. Finally, we demonstrated that EGF induces the expression of EMT markers in primary HLECs via a miR-26b-dependent mechanism. In summary, EGF activated Myc and Myc overexpression inhibited miR-26b by recruitment of HDAC3, which in turn induced the expression of EZH2 and promoted the progression of EMT in HLECs.

[Research progress of amphiregulin and its role in airway inflammatory disease].

Amphiregulin is a member of epidermal growth factor family, and is also one of the ligand of epidermal growth factor receptor, it participates in many physiological and pathological process by combining with EGFR. Researches have proved that AREG participates in asthma and airway inflammatory diseases caused by smoking and PM 2.5, and AREG plays an important role in the process of airway remodeling and inflammation. This paper mainly reviews the expression and function of AREG, and focus on it's research status in airway inflammatory disease.

The EGF/Ras pathway controls growth in Drosophila via ribosomal RNA synthesis.

The Ras small G-protein is a conserved regulator of cell and tissue growth during animal development. Studies in Drosophila have shown how Ras can stimulate a RAF-MEK-ERK signalling pathway to control cell growth and proliferation in response to Epidermal Growth Factor (EGF) stimulation. This work has also defined several transcription factors that can function as downstream growth effectors of the EGF/Ras/ERK pathway by stimulating mRNA transcription. Here we report on stimulation of RNA polymerase I (Pol I)-mediated ribosomal RNA (rRNA) synthesis as a growth effector of Ras/ERK signalling in Drosophila. We show that Ras/ERK signalling promotes an increase in nucleolar size in larval wing discs, which is indicative of increased ribosome synthesis. We also find that activation of Ras/ERK signalling promotes rRNA synthesis both in vivo and in cultured Drosophila S2 cells. We show that Ras signalling can regulate the expression of the Pol I transcription factor TIF-IA, and that this regulation requires dMyc. Finally, we find that TIF-IA-mediated rRNA synthesis is required for Ras/ERK signalling to drive proliferation in both larval and adult Drosophila tissues. These findings indicate that Ras signalling can promote ribosome synthesis in Drosophila, and that this is one mechanism that contributes to the growth effects of the Ras signalling pathway.