1
|
Evidence That Runt Acts as a Counter-Repressor of Groucho During Drosophila melanogaster Primary Sex Determination. G3-GENES GENOMES GENETICS 2020; 10:2487-2496. [PMID: 32457096 PMCID: PMC7341146 DOI: 10.1534/g3.120.401384] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Runx proteins are bifunctional transcription factors that both repress and activate transcription in animal cells. Typically, Runx proteins work in concert with other transcriptional regulators, including co-activators and co-repressors to mediate their biological effects. In Drosophila melanogaster the archetypal Runx protein, Runt, functions in numerous processes including segmentation, neurogenesis and sex determination. During primary sex determination Runt acts as one of four X-linked signal element (XSE) proteins that direct female-specific activation of the establishment promoter (Pe) of the master regulatory gene Sex-lethal (Sxl). Successful activation of SxlPe requires that the XSE proteins overcome the repressive effects of maternally deposited Groucho (Gro), a potent co-repressor of the Gro/TLE family. Runx proteins, including Runt, contain a C-terminal peptide, VWRPY, known to bind to Gro/TLE proteins to mediate transcriptional repression. We show that Runt’s VWRPY co-repressor-interaction domain is needed for Runt to activate SxlPe. Deletion of the Gro-interaction domain eliminates Runt-ability to activate SxlPe, whereas replacement with a higher affinity, VWRPW, sequence promotes Runt-mediated transcription. This suggests that Runt may activate SxlPe by antagonizing Gro function, a conclusion consistent with earlier findings that Runt is needed for Sxl expression only in embryonic regions with high Gro activity. Surprisingly we found that Runt is not required for the initial activation of SxlPe. Instead, Runt is needed to keep SxlPe active during the subsequent period of high-level Sxl transcription suggesting that Runt helps amplify the difference between female and male XSE signals by counter-repressing Gro in female, but not in male, embryos.
Collapse
|
2
|
Abstract
Terminal regions of the early Drosophila embryo are patterned by the highly conserved ERK cascade, giving rise to the nonsegmented terminal structures of the future larva. In less than an hour, this signaling event establishes several gene expression boundaries and sets in motion a sequence of elaborate morphogenetic events. Genetic studies of terminal patterning discovered signaling components and transcription factors that are involved in numerous developmental contexts and deregulated in human diseases. This review summarizes current understanding of signaling and morphogenesis during terminal patterning and discusses several open questions that can now be rigorously investigated using live imaging, omics, and optogenetic approaches. The anatomical simplicity of the terminal patterning system and its amenability to a broad range of increasingly sophisticated genetic perturbations will continue to make it a premier quantitative model for studying multiple aspects of tissue patterning by dynamically controlled cell signaling pathways.
Collapse
|
3
|
Receptor Tyrosine Kinases in Development: Insights from Drosophila. Int J Mol Sci 2019; 21:ijms21010188. [PMID: 31888080 PMCID: PMC6982143 DOI: 10.3390/ijms21010188] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 12/20/2019] [Accepted: 12/20/2019] [Indexed: 12/25/2022] Open
Abstract
Cell-to-cell communication mediates a plethora of cellular decisions and behaviors that are crucial for the correct and robust development of multicellular organisms. Many of these signals are encoded in secreted hormones or growth factors that bind to and activate cell surface receptors, to transmit the cue intracellularly. One of the major superfamilies of cell surface receptors are the receptor tyrosine kinases (RTKs). For nearly half a century RTKs have been the focus of intensive study due to their ability to alter fundamental aspects of cell biology, such as cell proliferation, growth, and shape, and because of their central importance in diseases such as cancer. Studies in model organisms such a Drosophila melanogaster have proved invaluable for identifying new conserved RTK pathway components, delineating their contributions, and for the discovery of conserved mechanisms that control RTK-signaling events. Here we provide a brief overview of the RTK superfamily and the general mechanisms used in their regulation. We further highlight the functions of several RTKs that govern distinct cell-fate decisions in Drosophila and explore how their activities are developmentally controlled.
Collapse
|
4
|
Abstract
The extracellular signal-regulated kinase (ERK) pathway leads to activation of the effector molecule ERK, which controls downstream responses by phosphorylating a variety of substrates, including transcription factors. Crucial insights into the regulation and function of this pathway came from studying embryos in which specific phenotypes arise from aberrant ERK activation. Despite decades of research, several important questions remain to be addressed for deeper understanding of this highly conserved signaling system and its function. Answering these questions will require quantifying the first steps of pathway activation, elucidating the mechanisms of transcriptional interpretation and measuring the quantitative limits of ERK signaling within which the system must operate to avoid developmental defects.
Collapse
Affiliation(s)
- Aleena L Patel
- Lewis Sigler Institute for Integrative Genomics, Department of Chemical Engineering, Princeton University, Princeton, NJ 08544, USA
| | - Stanislav Y Shvartsman
- Lewis Sigler Institute for Integrative Genomics, Department of Chemical Engineering, Princeton University, Princeton, NJ 08544, USA
| |
Collapse
|
5
|
Goyal Y, Schüpbach T, Shvartsman SY. A quantitative model of developmental RTK signaling. Dev Biol 2018; 442:80-86. [PMID: 30026122 DOI: 10.1016/j.ydbio.2018.07.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2018] [Revised: 06/22/2018] [Accepted: 07/13/2018] [Indexed: 01/06/2023]
Abstract
Receptor tyrosine kinases (RTKs) control a wide range of developmental processes, from the first stages of embryogenesis to postnatal growth and neurocognitive development in the adult. A significant share of our knowledge about RTKs comes from genetic screens in model organisms, which provided numerous examples demonstrating how specific cell fates and morphologies are abolished when RTK activation is either abrogated or significantly reduced. Aberrant activation of such pathways has also been recognized in many forms of cancer. More recently, studies of human developmental syndromes established that excessive activation of RTKs and their downstream signaling effectors, most notably the Ras signaling pathway, can also lead to structural and functional defects. Given that both insufficient and excessive pathway activation can lead to abnormalities, mechanistic analysis of developmental RTK signaling must address quantitative questions about its regulation and function. Patterning events controlled by the RTK Torso in the early Drosophila embryo are well-suited for this purpose. This mini review summarizes current state of knowledge about Torso-dependent Ras activation and discusses its potential to serve as a quantitative model for studying the general principles of Ras signaling in development and disease.
Collapse
Affiliation(s)
- Yogesh Goyal
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, United States; The Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, United States
| | - Trudi Schüpbach
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, United States
| | - Stanislav Y Shvartsman
- Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, United States; The Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, United States; Department of Molecular Biology, Princeton University, Princeton, NJ 08544, United States.
| |
Collapse
|
6
|
Webber JL, Zhang J, Massey A, Sanchez-Luege N, Rebay I. Collaborative repressive action of the antagonistic ETS transcription factors Pointed and Yan fine-tunes gene expression to confer robustness in Drosophila. Development 2018; 145:dev.165985. [PMID: 29848501 DOI: 10.1242/dev.165985] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 05/17/2018] [Indexed: 01/29/2023]
Abstract
The acquisition of cellular identity during development depends on precise spatiotemporal regulation of gene expression, with combinatorial interactions between transcription factors, accessory proteins and the basal transcription machinery together translating complex signaling inputs into appropriate gene expression outputs. The opposing repressive and activating inputs of the Drosophila ETS family transcription factors Yan and Pointed orchestrate numerous cell fate transitions downstream of receptor tyrosine kinase signaling, providing one of the premier systems for studying this process. Current models describe the differentiative transition as a switch from Yan-mediated repression to Pointed-mediated activation of common target genes. We describe here a new layer of regulation whereby Yan and Pointed co-occupy regulatory elements to repress gene expression in a coordinated manner, with Pointed being unexpectedly required for the genome-wide occupancy of both Yan and the co-repressor Groucho. Using even skipped as a test-case, synergistic genetic interactions between Pointed, Groucho, Yan and components of the RNA polymerase II pausing machinery suggest that Pointed integrates multiple scales of repressive regulation to confer robustness. We speculate that this mechanism may be used broadly to fine-tune the expression of many genes crucial for development.
Collapse
Affiliation(s)
- Jemma L Webber
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
| | - Jie Zhang
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
| | - Alex Massey
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
| | - Nicelio Sanchez-Luege
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
| | - Ilaria Rebay
- Ben May Department for Cancer Research, University of Chicago, Chicago, IL 60637, USA
| |
Collapse
|
7
|
Jussen D, von Hilchen J, Urbach R. Genetic regulation and function of epidermal growth factor receptor signalling in patterning of the embryonic Drosophila brain. Open Biol 2017; 6:rsob.160202. [PMID: 27974623 PMCID: PMC5204121 DOI: 10.1098/rsob.160202] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 11/14/2016] [Indexed: 01/16/2023] Open
Abstract
The specification of distinct neural cell types in central nervous system development crucially depends on positional cues conferred to neural stem cells in the neuroectoderm. Here, we investigate the regulation and function of the epidermal growth factor receptor (EGFR) signalling pathway in early development of the Drosophila brain. We find that localized EGFR signalling in the brain neuroectoderm relies on a neuromere-specific deployment of activating (Spitz, Vein) and inhibiting (Argos) ligands. Activated EGFR controls the spatially restricted expression of all dorsoventral (DV) patterning genes in a gene- and neuromere-specific manner. Further, we reveal a novel role of DV genes—ventral nervous system defective (vnd), intermediate neuroblast defective (ind), Nkx6—in regulating the expression of vein and argos, which feed back on EGFR, indicating that EGFR signalling stands not strictly atop the DV patterning genes. Within this network of genetic interactions, Vnd acts as a positive EGFR feedback regulator. Further, we show that EGFR signalling becomes dependent on single-minded-expressing midline cells in the posterior brain (tritocerebrum), but remains midline-independent in the anterior brain (deuto- and protocerebrum). Finally, we demonstrate that activated EGFR controls the proper formation of brain neuroblasts by regulating the number, survival and proneural gene expression of neuroectodermal progenitor cells. These data demonstrate that EGFR signalling is crucially important for patterning and early neurogenesis of the brain.
Collapse
Affiliation(s)
- David Jussen
- Institute of Genetics, University of Mainz, 55099 Mainz, Germany
| | | | - Rolf Urbach
- Institute of Genetics, University of Mainz, 55099 Mainz, Germany
| |
Collapse
|
8
|
Zahavi T, Maimon A, Kushnir T, Lange R, Berger E, Kornspan D, Grossman R, Anzi S, Shaulian E, Karni R, Nechushtan H, Paroush Z. Ras-Erk signaling induces phosphorylation of human TLE1 and downregulates its repressor function. Oncogene 2017; 36:3729-3739. [PMID: 28192406 DOI: 10.1038/onc.2016.517] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2016] [Revised: 12/11/2016] [Accepted: 12/21/2016] [Indexed: 11/09/2022]
Abstract
Signaling mediated by the Ras-extracellular signal-regulated kinase (Erk) pathway often leads to the phosphorylation of transcriptional regulators, thereby modulating their activity and causing concerted changes in gene expression. In Drosophila, the induction of multiple Ras-Erk pathway target genes depends on prior phosphorylation of the general co-repressor Groucho, a modification that downregulates its repressive function. Here, we show that TLE1, one of the four human Groucho orthologs, is similarly phosphorylated in response to Ras-Erk pathway activation, and that this modification attenuates its capacity to repress transcription. Specifically, unphosphorylated TLE1 dominantly suppresses the induction of Ras-Erk pathway target genes in cultured human cells, and the expression of an unphosphorylatable TLE1 derivative causes severe phenotypes in a transgenic Drosophila model system, whereas a phosphomimetic variant of TLE1 exerts only negligible effects. We present data indicating that TLE1 is rapidly excluded from the nucleus following epidermal growth factor receptor pathway activation, an effect that likely accounts for its inability to mediate effective repression under such conditions. Significantly, we find that unphosphorylated TLE1 blocks oncogenic phenotypes induced by mutated H-Ras in human mammary cells, both in vitro and following their implantation in mice. Collectively, our data strongly indicate that phosphorylation of TLE family members and the consequent downregulation of their repressor function is a key conserved step in the transcriptional responses to Ras-Erk signaling, and possibly a critical event in the tumorigenic effects caused by excessive Ras-Erk pathway activity.
Collapse
Affiliation(s)
- T Zahavi
- Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - A Maimon
- Department of Biochemistry and Molecular Biology, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - T Kushnir
- Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - R Lange
- Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - E Berger
- Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - D Kornspan
- Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel.,Department of Oncology, Sharett Institute of Oncology, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - R Grossman
- Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - S Anzi
- Department of Biochemistry and Molecular Biology, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - E Shaulian
- Department of Biochemistry and Molecular Biology, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - R Karni
- Department of Biochemistry and Molecular Biology, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| | - H Nechushtan
- Department of Oncology, Sharett Institute of Oncology, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Z Paroush
- Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
| |
Collapse
|
9
|
Johnston MJ, Bar-Cohen S, Paroush Z, Nystul TG. Phosphorylated Groucho delays differentiation in the follicle stem cell lineage by providing a molecular memory of EGFR signaling in the niche. Development 2016; 143:4631-4642. [PMID: 27836963 PMCID: PMC5201033 DOI: 10.1242/dev.143263] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Accepted: 10/31/2016] [Indexed: 01/03/2023]
Abstract
In the epithelial follicle stem cells (FSCs) of the Drosophila ovary, Epidermal Growth Factor Receptor (EGFR) signaling promotes self-renewal, whereas Notch signaling promotes differentiation of the prefollicle cell (pFC) daughters. We have identified two proteins, Six4 and Groucho (Gro), that link the activity of these two pathways to regulate the earliest cell fate decision in the FSC lineage. Our data indicate that Six4 and Gro promote differentiation towards the polar cell fate by promoting Notch pathway activity. This activity of Gro is antagonized by EGFR signaling, which inhibits Gro-dependent repression via p-ERK mediated phosphorylation. We have found that the phosphorylated form of Gro persists in newly formed pFCs, which may delay differentiation and provide these cells with a temporary memory of the EGFR signal. Collectively, these findings demonstrate that phosphorylated Gro labels a transition state in the FSC lineage and describe the interplay between Notch and EGFR signaling that governs the differentiation processes during this period.
Collapse
Affiliation(s)
- Michael J Johnston
- The University of California, San Francisco, Departments of Anatomy and OB-GYN/RS, CA 94122, USA
| | - Shaked Bar-Cohen
- The Hebrew University, Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, Jerusalem 9112102, Israel
| | - Ze'ev Paroush
- The Hebrew University, Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, Jerusalem 9112102, Israel
| | - Todd G Nystul
- The University of California, San Francisco, Departments of Anatomy and OB-GYN/RS, CA 94122, USA
| |
Collapse
|
10
|
Zhang T, Du W. Groucho restricts rhomboid expression and couples EGFR activation with R8 selection during Drosophila photoreceptor differentiation. Dev Biol 2015; 407:246-55. [PMID: 26417727 DOI: 10.1016/j.ydbio.2015.09.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Revised: 07/18/2015] [Accepted: 09/24/2015] [Indexed: 11/17/2022]
Abstract
Notch and EGFR signaling pathways play important roles in photoreceptor differentiation during Drosophila eye development. Notch signaling induces Enhancer of Split (E(spl)) proteins to repress atonal (ato) expression and restrict R8 photoreceptor cell fate. The R8 precursors express rhomboid (rho), which is required for the release of active EGFR ligand to activate EGFR signaling in surrounding cells for the subsequent stepwise recruitment. However, it is not clear about the mechanisms of transcriptional regulation of rho and how the lateral inhibition of Notch signaling and rho expression are coordinated. In this study, we show that inactivation of Groucho (Gro), an evolutionally conserved transcriptional corepressor, inhibits Ato upregulation, delays R8 determination, and promotes differentiation of R2-5 type of neurons. We demonstrate that these phenotypes are caused by a combination of the loss of Notch-mediated lateral inhibition and the precocious activation of EGFR signaling due to deregulated rho expression. Blocking EGFR signaling by Pnt-RNAi in conjunction with Gro-inactivation leads to lateral inhibition defects with deregulated Ato expression and R8 differentiation. We further show that inactivation of E(spl), which are the Gro binding transcription factors, causes deregulated rho expression and extra R8 cells within and posterior to the morphogenetic furrow (MF), and that E(spl) mediates the binding of Gro to the regulatory regions of both rho and ato genes in eye disc cells. Our results suggest that Gro inhibits rho expression in undifferentiated cells and represses the expression of both ato and rho in non-R8 precursors during initiation of photoreceptor differentiation in an E(spl)-dependent manner. The latter function of Gro provides novel insights into the mechanism that coordinates R8 specification with the restriction of initial rho expression to developing R8 cells.
Collapse
Affiliation(s)
- Tianyi Zhang
- Ben May Department for Cancer Research, The University of Chicago, 929 E. 57th Street, Chicago, IL 60637, USA
| | - Wei Du
- Ben May Department for Cancer Research, The University of Chicago, 929 E. 57th Street, Chicago, IL 60637, USA.
| |
Collapse
|
11
|
Rhomboid Enhancer Activity Defines a Subset of Drosophila Neural Precursors Required for Proper Feeding, Growth and Viability. PLoS One 2015; 10:e0134915. [PMID: 26252385 PMCID: PMC4529294 DOI: 10.1371/journal.pone.0134915] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2014] [Accepted: 07/15/2015] [Indexed: 11/19/2022] Open
Abstract
Organismal growth regulation requires the interaction of multiple metabolic, hormonal and neuronal pathways. While the molecular basis for many of these are well characterized, less is known about the developmental origins of growth regulatory structures and the mechanisms governing control of feeding and satiety. For these reasons, new tools and approaches are needed to link the specification and maturation of discrete cell populations with their subsequent regulatory roles. In this study, we characterize a rhomboid enhancer element that selectively labels four Drosophila embryonic neural precursors. These precursors give rise to the hypopharyngeal sensory organ of the peripheral nervous system and a subset of neurons in the deutocerebral region of the embryonic central nervous system. Post embryogenesis, the rhomboid enhancer is active in a subset of cells within the larval pharyngeal epithelium. Enhancer-targeted toxin expression alters the morphology of the sense organ and results in impaired larval growth, developmental delay, defective anterior spiracle eversion and lethality. Limiting the duration of toxin expression reveals differences in the critical periods for these effects. Embryonic expression causes developmental defects and partially penetrant pre-pupal lethality. Survivors of embryonic expression, however, ultimately become viable adults. In contrast, post-embryonic toxin expression results in fully penetrant lethality. To better define the larval growth defect, we used a variety of assays to demonstrate that toxin-targeted larvae are capable of locating, ingesting and clearing food and they exhibit normal food search behaviors. Strikingly, however, following food exposure these larvae show a rapid decrease in consumption suggesting a satiety-like phenomenon that correlates with the period of impaired larval growth. Together, these data suggest a critical role for these enhancer-defined lineages in regulating feeding, growth and viability.
Collapse
|
12
|
Origins of context-dependent gene repression by capicua. PLoS Genet 2015; 11:e1004902. [PMID: 25569482 PMCID: PMC4287436 DOI: 10.1371/journal.pgen.1004902] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Accepted: 11/17/2014] [Indexed: 12/23/2022] Open
Abstract
Receptor Tyrosine Kinase (RTK) signaling pathways induce multiple biological responses, often by regulating the expression of downstream genes. The HMG-box protein Capicua (Cic) is a transcriptional repressor that is downregulated in response to RTK signaling, thereby enabling RTK-dependent induction of Cic targets. In both Drosophila and mammals, Cic is expressed as two isoforms, long (Cic-L) and short (Cic-S), whose functional significance and mechanism of action are not well understood. Here we show that Drosophila Cic relies on the Groucho (Gro) corepressor during its function in the early embryo, but not during other stages of development. This Gro-dependent mechanism requires a short peptide motif, unique to Cic-S and designated N2, which is distinct from other previously defined Gro-interacting motifs and functions as an autonomous, transferable repressor element. Unexpectedly, our data indicate that the N2 motif is an evolutionary innovation that originated within dipteran insects, as the Cic-S isoform evolved from an ancestral Cic-L-type form. Accordingly, the Cic-L isoform lacking the N2 motif is completely inactive in early Drosophila embryos, indicating that the N2 motif endowed Cic-S with a novel Gro-dependent activity that is obligatory at this stage. We suggest that Cic-S and Gro coregulatory functions have facilitated the evolution of the complex transcriptional network regulated by Torso RTK signaling in modern fly embryos. Notably, our results also imply that mammalian Cic proteins are unlikely to act via Gro and that their Cic-S isoform must have evolved independently of fly Cic-S. Thus, Cic proteins employ distinct repressor mechanisms that are associated with discrete structural changes in the evolutionary history of this protein family. Understanding the evolution of developmental regulatory mechanisms is a central challenge of biology. Here we uncover a newly evolved mechanism of transcriptional repression by Capicua (Cic), a conserved sensor of Receptor Tyrosine Kinase (RTK) signaling. In Drosophila, Cic patterns the central regions of the embryo by repressing genes induced by Torso RTK signaling at the poles. We show that Cic performs this function by recruiting the Groucho (Gro) corepressor and that this mechanism is an evolutionary innovation of dipteran insects. Indeed, we find that recruitment of Gro depends on a short motif of Cic (N2) specific to dipterans. Strikingly, moreover, the form of Cic that existed before the origin of dipterans is completely inactive in fly embryos, whereas the equivalent form carrying N2 displays significant function. This suggests that evolution of the N2 motif caused a fundamental change in Cic repressor activity, which we propose has enabled the complex roles of Cic, Gro and Torso signaling in fly embryonic patterning. In contrast, Cic functions independently of Gro in other Drosophila tissues and probably also in mammals, where Cic lacks the N2 sequence. Thus, our results illustrate the structural and evolutionary origins of essential functional variations within a highly conserved family of developmental regulators.
Collapse
|
13
|
Shilo BZ. The regulation and functions of MAPK pathways in Drosophila. Methods 2014; 68:151-9. [DOI: 10.1016/j.ymeth.2014.01.020] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Revised: 01/30/2014] [Accepted: 01/31/2014] [Indexed: 11/26/2022] Open
|
14
|
|
15
|
Mannervik M. Control of Drosophila embryo patterning by transcriptional co-regulators. Exp Cell Res 2013; 321:47-57. [PMID: 24157250 DOI: 10.1016/j.yexcr.2013.10.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2013] [Revised: 10/10/2013] [Accepted: 10/14/2013] [Indexed: 12/29/2022]
Abstract
A combination of broadly expressed transcriptional activators and spatially restricted repressors are used to pattern embryos into cells of different fate. Transcriptional co-regulators are essential mediators of transcription factor function, and contribute to selective transcriptional responses in embryo development. A two step mechanism of transcriptional regulation is discussed, where remodeling of chromatin is initially required, followed by stimulation of recruitment or release of RNA polymerase from the promoter. Transcriptional co-regulators are essential for both of these steps. In particular, most co-activators are associated with histone acetylation and co-repressors with histone deacetylation. In the early Drosophila embryo, genome-wide studies have shown that the CBP co-activator has a preference for associating with some transcription factors and regulatory regions. The Groucho, CtBP, Ebi, Atrophin and Brakeless co-repressors are selectively used to limit zygotic gene expression. New findings are summarized which show that different co-repressors are often utilized by a single repressor, that the context in which a co-repressor is recruited to DNA can affect its activity, and that co-regulators may switch from co-repressors to co-activators and vice versa. The possibility that co-regulator activity is regulated and plays an instructive role in development is discussed as well. This review highlights how findings in Drosophila embryos have contributed to the understanding of transcriptional regulation in eukaryotes as well as to mechanisms of animal embryo patterning.
Collapse
Affiliation(s)
- Mattias Mannervik
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Arrheniuslaboratories E3, SE-106 91 Stockholm, Sweden.
| |
Collapse
|
16
|
Shwartz A, Yogev S, Schejter ED, Shilo BZ. Sequential activation of ETS proteins provides a sustained transcriptional response to EGFR signaling. Development 2013; 140:2746-54. [PMID: 23757412 DOI: 10.1242/dev.093138] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
How signal transduction, which is dynamic and fluctuating by nature, is converted into a stable trancriptional response, is an unanswered question in developmental biology. Two ETS-domain transcription factors encoded by the pointed (pnt) locus, PntP1 and PntP2, are universal downstream mediators of EGFR-based signaling in Drosophila. Full disruption of pnt function in developing eye imaginal discs reveals a photoreceptor recruitment phenotype, in which only the R8 photoreceptor cell type is specified within ommatidia. Specific disruption of either pntP1 or pntP2 resulted in the same R8-only phenotype, demonstrating that both Pnt isoforms are essential for photoreceptor recruitment. We show that the two Pnt protein forms are activated in a sequential manner within the EGFR signaling pathway: MAPK phosphorylates and activates PntP2, which in turn induces pntP1 transcription. Once expressed, PntP1 is constitutively active and sufficient to induce target genes essential for photoreceptor development. Pulse-chase experiments indicate that PntP1 is stable for several hours in the eye disc. Sequential ETS-protein recruitment therefore allows sustained induction of target genes, beyond the transient activation of EGFR.
Collapse
Affiliation(s)
- Arkadi Shwartz
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel
| | | | | | | |
Collapse
|
17
|
Abstract
Tyrosine phosphorylation plays a significant role in a wide range of cellular processes. The Drosophila genome encodes more than 20 receptor tyrosine kinases and extensive studies in the past 20 years have illustrated their diverse roles and complex signaling mechanisms. Although some receptor tyrosine kinases have highly specific functions, others strikingly are used in rather ubiquitous manners. Receptor tyrosine kinases regulate a broad expanse of processes, ranging from cell survival and proliferation to differentiation and patterning. Remarkably, different receptor tyrosine kinases share many of the same effectors and their hierarchical organization is retained in disparate biological contexts. In this comprehensive review, we summarize what is known regarding each receptor tyrosine kinase during Drosophila development. Astonishingly, very little is known for approximately half of all Drosophila receptor tyrosine kinases.
Collapse
Affiliation(s)
- Richelle Sopko
- Department of Genetics, Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts 02115, USA
| | | |
Collapse
|
18
|
Jiménez G, Shvartsman SY, Paroush Z. The Capicua repressor--a general sensor of RTK signaling in development and disease. J Cell Sci 2013; 125:1383-91. [PMID: 22526417 DOI: 10.1242/jcs.092965] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Receptor tyrosine kinase (RTK) signaling pathways control multiple cellular decisions in metazoans, often by regulating the expression of downstream genes. In Drosophila melanogaster and other systems, E-twenty-six (ETS) transcription factors are considered to be the predominant nuclear effectors of RTK pathways. Here, we highlight recent progress in identifying the HMG-box protein Capicua (CIC) as a key sensor of RTK signaling in both Drosophila and mammals. Several studies have shown that CIC functions as a repressor of RTK-responsive genes, keeping them silent in the absence of signaling. Following the activation of RTK signaling, CIC repression is relieved, and this allows the expression of the targeted gene in response to local or ubiquitous activators. This regulatory switch is essential for several RTK responses in Drosophila, from the determination of cell fate to cell proliferation. Furthermore, increasing evidence supports the notion that this mechanism is conserved in mammals, where CIC has been implicated in cancer and neurodegeneration. In addition to summarizing our current knowledge on CIC, we also discuss the implications of these findings for our understanding of RTK signaling specificity in different biological processes.
Collapse
Affiliation(s)
- Gerardo Jiménez
- Institució Catalana de Recerca i Estudis Avançats and Institut de Biologia Molecular de Barcelona-CSIC, Parc Científic de Barcelona, Barcelona 08028, Spain.
| | | | | |
Collapse
|
19
|
Helman A, Lim B, Andreu MJ, Kim Y, Shestkin T, Lu H, Jiménez G, Shvartsman SY, Paroush Z. RTK signaling modulates the Dorsal gradient. Development 2012; 139:3032-9. [PMID: 22791891 DOI: 10.1242/dev.075812] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The dorsoventral (DV) axis of the Drosophila embryo is patterned by a nuclear gradient of the Rel family transcription factor, Dorsal (Dl), that activates or represses numerous target genes in a region-specific manner. Here, we demonstrate that signaling by receptor tyrosine kinases (RTK) reduces nuclear levels and transcriptional activity of Dl, both at the poles and in the mid-body of the embryo. These effects depend on wntD, which encodes a Dl antagonist belonging to the Wingless/Wnt family of secreted factors. Specifically, we show that, via relief of Groucho- and Capicua-mediated repression, the Torso and EGFR RTK pathways induce expression of WntD, which in turn limits Dl nuclear localization at the poles and along the DV axis. Furthermore, this RTK-dependent control of Dl is important for restricting expression of its targets in both contexts. Thus, our results reveal a new mechanism of crosstalk, whereby RTK signals modulate the spatial distribution and activity of a developmental morphogen in vivo.
Collapse
Affiliation(s)
- Aharon Helman
- Department of Developmental Biology and Cancer Research, IMRIC, Faculty of Medicine, The Hebrew University, Jerusalem 91120, Israel
| | | | | | | | | | | | | | | | | |
Collapse
|
20
|
Abstract
Drosophila Groucho (Gro) is the founding member of a family of metazoan corepressors. Gro mediates repression through interactions with a myriad of DNA-binding repressor proteins to direct the silencing of genes involved in many developmental processes, including neurogenesis and patterning of the main body axis, as well as receptor tyrosine kinase/Ras/MAPK, Notch, Wingless (Wg)/Wnt, and Decapentaplegic (Dpp) signaling. Gro mediates repression by multiple molecular mechanisms, depending on the regulatory context. Because Gro is a broadly expressed nuclear factor, whereas its repressor partners display restricted temporal and spatial distribution, it was presumed that this corepressor played permissive rather than instructive roles in development. However, a wide range of studies demonstrates that this is not the case. Gro can sense and integrate many cellular inputs to modulate the expression of variety of genes, making it a versatile corepressor with crucial instructive roles in development and signaling.
Collapse
Affiliation(s)
- Wiam Turki-Judeh
- Department of Chemistry & Biochemistry and Molecular Biology Institute, University of California, Los Angeles, California, USA
| | | |
Collapse
|
21
|
Moses C, Helman A, Paroush Z, Von Ohlen T. Phosphorylation of Ind by MAP kinase enhances Ind-dependent transcriptional repression. Dev Biol 2011; 360:208-15. [PMID: 21983201 DOI: 10.1016/j.ydbio.2011.09.022] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 09/20/2011] [Accepted: 09/21/2011] [Indexed: 10/17/2022]
Abstract
The Drosophila neuroectoderm is initially subdivided into three longitudinal domains that give rise to columns of neuroblasts. This subdivision is coordinately accomplished by the action of the signaling pathways, Dorsal and Epidermal Growth Factor Receptor (EGFR), in conjunction with the homeodomain proteins, Ventral nervous system defective, Intermediate neuroblasts defective (Ind) and Muscle Segment Homeobox. We previously demonstrated that Ind expression is activated in response to the EGFR pathway. Here we show that EGF signaling subsequently mediates the direct phosphorylation of Ind by MAP kinase, which enhances the capacity of Ind to repress target genes, such as achaete. Specifically, we show that reduced EGF signaling results in diminished repression of achaete in the intermediate column, despite the presence of high levels of Ind protein. We also demonstrate that ectopic activation of MAP kinase results in the lateral expansion of the Ind expression domain with a corresponding reduction in achaete expression. This regulation is also dependent on the co-repressor, Dichaete. Our data indicate that EGF signaling, acting through MAP kinase, impinges on multiple aspects of Ind regulatory activity. While it has been often demonstrated that MAP kinase phosphorylation of transcriptional repressors attenuates their repressor activity, here we provide an example of phosphorylation enhancing repressor activity.
Collapse
Affiliation(s)
- Cade Moses
- Kansas State University, College of Veterinary Medicine, Diagnostic Medicine and Pathobiology, Manhattan, KS 66506, USA
| | | | | | | |
Collapse
|