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Jackson JA, Denk-Lobnig M, Kitzinger KA, Martin AC. Change in RhoGAP and RhoGEF availability drives transitions in cortical patterning and excitability in Drosophila. Curr Biol 2024; 34:2132-2146.e5. [PMID: 38688282 PMCID: PMC11111359 DOI: 10.1016/j.cub.2024.04.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2023] [Revised: 02/13/2024] [Accepted: 04/09/2024] [Indexed: 05/02/2024]
Abstract
Actin cortex patterning and dynamics are critical for cell shape changes. These dynamics undergo transitions during development, often accompanying changes in collective cell behavior. Although mechanisms have been established for individual cells' dynamic behaviors, the mechanisms and specific molecules that result in developmental transitions in vivo are still poorly understood. Here, we took advantage of two developmental systems in Drosophila melanogaster to identify conditions that altered cortical patterning and dynamics. We identified a Rho guanine nucleotide exchange factor (RhoGEF) and Rho GTPase activating protein (RhoGAP) pair required for actomyosin waves in egg chambers. Specifically, depletion of the RhoGEF, Ect2, or the RhoGAP, RhoGAP15B, disrupted actomyosin wave induction, and both proteins relocalized from the nucleus to the cortex preceding wave formation. Furthermore, we found that overexpression of a different RhoGEF and RhoGAP pair, RhoGEF2 and Cumberland GAP (C-GAP), resulted in actomyosin waves in the early embryo, during which RhoA activation precedes actomyosin assembly by ∼4 s. We found that C-GAP was recruited to actomyosin waves, and disrupting F-actin polymerization altered the spatial organization of both RhoA signaling and the cytoskeleton in waves. In addition, disrupting F-actin dynamics increased wave period and width, consistent with a possible role for F-actin in promoting delayed negative feedback. Overall, we showed a mechanism involved in inducing actomyosin waves that is essential for oocyte development and is general to other cell types, such as epithelial and syncytial cells.
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Affiliation(s)
- Jonathan A Jackson
- Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA; Graduate Program in Biophysics, Harvard University, 86 Brattle Street, Cambridge, MA 02138, USA
| | - Marlis Denk-Lobnig
- Department of Biophysics, University of Michigan, 1109 Geddes Ave., Ann Arbor, MI 48109, USA
| | - Katherine A Kitzinger
- Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA
| | - Adam C Martin
- Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA.
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2
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Rosa-Birriel C, Malin J, Hatini V. Medioapical contractile pulses coordinated between cells regulate Drosophila eye morphogenesis. J Cell Biol 2024; 223:e202304041. [PMID: 38126997 PMCID: PMC10737437 DOI: 10.1083/jcb.202304041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Revised: 10/31/2023] [Accepted: 12/07/2023] [Indexed: 12/23/2023] Open
Abstract
Lattice cells (LCs) in the developing Drosophila retina change shape before attaining final form. Previously, we showed that repeated contraction and expansion of apical cell contacts affect these dynamics. Here, we describe another factor, the assembly of a Rho1-dependent medioapical actomyosin ring formed by nodes linked by filaments that contract the apical cell area. Cell area contraction alternates with relaxation, generating pulsatile changes in cell area that exert force on neighboring LCs. Moreover, Rho1 signaling is sensitive to mechanical changes, becoming active when tension decreases and cells expand, while the negative regulator RhoGAP71E accumulates when tension increases and cells contract. This results in cycles of cell area contraction and relaxation that are reciprocally synchronized between adjacent LCs. Thus, mechanically sensitive Rho1 signaling controls pulsatile medioapical actomyosin contraction and coordinates cell behavior across the epithelium. Disrupting the kinetics of pulsing can lead to developmental errors, suggesting this process controls cell shape and tissue integrity during epithelial morphogenesis of the retina.
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Affiliation(s)
- Christian Rosa-Birriel
- Department of Developmental, Molecular and Chemical Biology, Program in Cell, Molecular and Developmental Biology, Program in Genetics, and Program in Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA, USA
| | - Jacob Malin
- Department of Developmental, Molecular and Chemical Biology, Program in Cell, Molecular and Developmental Biology, Program in Genetics, and Program in Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA, USA
| | - Victor Hatini
- Department of Developmental, Molecular and Chemical Biology, Program in Cell, Molecular and Developmental Biology, Program in Genetics, and Program in Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA, USA
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3
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Jackson JA, Denk-Lobnig M, Kitzinger KA, Martin AC. Change in RhoGAP and RhoGEF availability drives transitions in cortical patterning and excitability in Drosophila. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.06.565883. [PMID: 37986763 PMCID: PMC10659369 DOI: 10.1101/2023.11.06.565883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
Actin cortex patterning and dynamics are critical for cell shape changes. These dynamics undergo transitions during development, often accompanying changes in collective cell behavior. While mechanisms have been established for individual cells' dynamic behaviors, mechanisms and specific molecules that result in developmental transitions in vivo are still poorly understood. Here, we took advantage of two developmental systems in Drosophila melanogaster to identify conditions that altered cortical patterning and dynamics. We identified a RhoGEF and RhoGAP pair whose relocalization from nucleus to cortex results in actomyosin waves in egg chambers. Furthermore, we found that overexpression of a different RhoGEF and RhoGAP pair resulted in actomyosin waves in the early embryo, during which RhoA activation precedes actomyosin assembly and RhoGAP recruitment by ~4 seconds. Overall, we showed a mechanism involved in inducing actomyosin waves that is essential for oocyte development and is general to other cell types.
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Affiliation(s)
- Jonathan A. Jackson
- Department of Biology, Massachusetts Institute of Technology
- Graduate Program in Biophysics, Harvard University
| | | | | | - Adam C. Martin
- Department of Biology, Massachusetts Institute of Technology
- Lead contact
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Rosa C, Malin J, Hatini V. Medioapical contractile pulses coordinated between cells regulate Drosophila eye morphogenesis. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.17.529936. [PMID: 36993651 PMCID: PMC10055172 DOI: 10.1101/2023.03.17.529936] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Lattice cells (LCs) in the developing Drosophila retina constantly move and change shape before attaining final forms. Previously we showed that repeated contraction and expansion of apical cell contacts affect these dynamics. Here we describe a second contributing factor, the assembly of a medioapical actomyosin ring composed of nodes linked by filaments that attract each other, fuse, and contract the LCs' apical area. This medioapical actomyosin network is dependent on Rho1 and its known effectors. Apical cell area contraction alternates with relaxation, generating pulsatile changes in apical cell area. Strikingly, cycles of contraction and relaxation of cell area are reciprocally synchronized between adjacent LCs. Further, in a genetic screen, we identified RhoGEF2 as an activator of these Rho1 functions and RhoGAP71E/C-GAP as an inhibitor. Thus, Rho1 signaling regulates pulsatile medioapical actomyosin contraction exerting force on neighboring cells, coordinating cell behavior across the epithelium. This ultimately serves to control cell shape and maintain tissue integrity during epithelial morphogenesis of the retina.
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5
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Sloan MA, Sadlova J, Lestinova T, Sanders MJ, Cotton JA, Volf P, Ligoxygakis P. The Phlebotomus papatasi systemic transcriptional response to trypanosomatid-contaminated blood does not differ from the non-infected blood meal. Parasit Vectors 2021; 14:15. [PMID: 33407867 PMCID: PMC7789365 DOI: 10.1186/s13071-020-04498-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Accepted: 11/23/2020] [Indexed: 02/13/2023] Open
Abstract
Background Leishmaniasis, caused by parasites of the genus Leishmania, is a disease that affects up to 8 million people worldwide. Parasites are transmitted to human and animal hosts through the bite of an infected sand fly. Novel strategies for disease control require a better understanding of the key step for transmission, namely the establishment of infection inside the fly. Methods The aim of this work was to identify sand fly systemic transcriptomic signatures associated with Leishmania infection. We used next generation sequencing to describe the transcriptome of whole Phlebotomus papatasi sand flies when fed with blood alone (control) or with blood containing one of three trypanosomatids: Leishmania major, L. donovani and Herpetomonas muscarum, the latter being a parasite not transmitted to humans. Results Of the trypanosomatids studied, only L. major was able to successfully establish an infection in the host P. papatasi. However, the transcriptional signatures observed after each parasite-contaminated blood meal were not specific to success or failure of a specific infection and they did not differ from each other. The transcriptional signatures were also indistinguishable after a non-contaminated blood meal. Conclusions The results imply that sand flies perceive Leishmania as just one feature of their microbiome landscape and that any strategy to tackle transmission should focus on the response towards the blood meal rather than parasite establishment. Alternatively, Leishmania could suppress host responses. These results will generate new thinking around the concept of stopping transmission by controlling the parasite inside the insect.![]()
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Affiliation(s)
- Megan A Sloan
- Department of Biochemistry, University of Oxford, South Parks Rd, Oxford, OX1 3QU, UK
| | - Jovana Sadlova
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Tereza Lestinova
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Mandy J Sanders
- The Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, CB10 1SA, Cambridgeshire, UK
| | - James A Cotton
- The Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, CB10 1SA, Cambridgeshire, UK
| | - Petr Volf
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Petros Ligoxygakis
- Department of Biochemistry, University of Oxford, South Parks Rd, Oxford, OX1 3QU, UK.
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6
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Role of Notch Signaling in Leg Development in Drosophila melanogaster. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1218:103-127. [PMID: 32060874 DOI: 10.1007/978-3-030-34436-8_7] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Notch pathway plays diverse and fundamental roles during animal development. One of the most relevant, which arises directly from its unique mode of activation, is the specification of cell fates and tissue boundaries. The development of the leg of Drosophila melanogaster is a fine example of this Notch function, as it is required to specify the fate of the cells that will eventually form the leg joints, the flexible structures that separate the different segments of the adult leg. Notch activity is accurately activated and maintained at the distal end of each segment in response to the proximo-distal patterning gene network of the developing leg. Region-specific downstream targets of Notch in turn regulate the formation of the different types of joints. We discuss recent findings that shed light on the molecular and cellular mechanisms that are ultimately governed by Notch to achieve epithelial fold and joint morphogenesis. Finally, we briefly summarize the role that Notch plays in inducing the nonautonomous growth of the leg. Overall, this book chapter aims to highlight leg development as a useful model to study how patterning information is translated into specific cell behaviors that shape the final form of an adult organ.
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Garcia De Las Bayonas A, Philippe JM, Lellouch AC, Lecuit T. Distinct RhoGEFs Activate Apical and Junctional Contractility under Control of G Proteins during Epithelial Morphogenesis. Curr Biol 2019; 29:3370-3385.e7. [PMID: 31522942 PMCID: PMC6839405 DOI: 10.1016/j.cub.2019.08.017] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Revised: 07/15/2019] [Accepted: 08/07/2019] [Indexed: 01/08/2023]
Abstract
Small RhoGTPases direct cell shape changes and movements during tissue morphogenesis. Their activities are tightly regulated in space and time to specify the desired pattern of actomyosin contractility that supports tissue morphogenesis. This is expected to stem from polarized surface stimuli and from polarized signaling processing inside cells. We examined this general problem in the context of cell intercalation that drives extension of the Drosophila ectoderm. In the ectoderm, G protein-coupled receptors (GPCRs) and their downstream heterotrimeric G proteins (Gα and Gβγ) activate Rho1 both medial-apically, where it exhibits pulsed dynamics, and at junctions, where its activity is planar polarized. However, the mechanisms responsible for polarizing Rho1 activity are unclear. We report that distinct guanine exchange factors (GEFs) activate Rho1 in these two cellular compartments. RhoGEF2 acts uniquely to activate medial-apical Rho1 but is recruited both medial-apically and at junctions by Gα12/13-GTP, also called Concertina (Cta) in Drosophila. On the other hand, Dp114RhoGEF (Dp114), a newly characterized RhoGEF, is required for cell intercalation in the extending ectoderm, where it activates Rho1 specifically at junctions. Its localization is restricted to adherens junctions and is under Gβ13F/Gγ1 control. Furthermore, Gβ13F/Gγ1 activates junctional Rho1 and exerts quantitative control over planar polarization of Rho1. Finally, we found that Dp114RhoGEF is absent in the mesoderm, arguing for a tissue-specific control over junctional Rho1 activity. These results clarify the mechanisms of polarization of Rho1 activity in different cellular compartments and reveal that distinct GEFs are sensitive tuning parameters of cell contractility in remodeling epithelia. Dp114RhoGEF activates junctional Rho1 and is involved in cell intercalation Gα/Cta and Gβγ subunits tune, respectively, RhoGEF2 and Dp114RhoGEF membrane levels Gβγ subunits control planar polarity of junctional Rho1 signaling via Dp114RhoGEF Tissue-specific RhoGEFs could diversify morphogenesis in different tissues
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Affiliation(s)
| | - Jean-Marc Philippe
- Aix Marseille Université, CNRS, IBDM-UMR7288, Turing Center for Living Systems, 13009 Marseille, France
| | - Annemarie C Lellouch
- Aix Marseille Université, CNRS, IBDM-UMR7288, Turing Center for Living Systems, 13009 Marseille, France
| | - Thomas Lecuit
- Aix Marseille Université, CNRS, IBDM-UMR7288, Turing Center for Living Systems, 13009 Marseille, France; Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France.
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8
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Silver JT, Wirtz-Peitz F, Simões S, Pellikka M, Yan D, Binari R, Nishimura T, Li Y, Harris TJC, Perrimon N, Tepass U. Apical polarity proteins recruit the RhoGEF Cysts to promote junctional myosin assembly. J Cell Biol 2019; 218:3397-3414. [PMID: 31409654 PMCID: PMC6781438 DOI: 10.1083/jcb.201807106] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2018] [Revised: 04/20/2019] [Accepted: 07/29/2019] [Indexed: 12/20/2022] Open
Abstract
Silver et al. show that the RhoGEF Cysts links apical polarity proteins to Rho1 and myosin activation at adherens junctions to support junctional and epithelial integrity in the Drosophila ectoderm. The spatio-temporal regulation of small Rho GTPases is crucial for the dynamic stability of epithelial tissues. However, how RhoGTPase activity is controlled during development remains largely unknown. To explore the regulation of Rho GTPases in vivo, we analyzed the Rho GTPase guanine nucleotide exchange factor (RhoGEF) Cysts, the Drosophila orthologue of mammalian p114RhoGEF, GEF-H1, p190RhoGEF, and AKAP-13. Loss of Cysts causes a phenotype that closely resembles the mutant phenotype of the apical polarity regulator Crumbs. This phenotype can be suppressed by the loss of basolateral polarity proteins, suggesting that Cysts is an integral component of the apical polarity protein network. We demonstrate that Cysts is recruited to the apico-lateral membrane through interactions with the Crumbs complex and Bazooka/Par3. Cysts activates Rho1 at adherens junctions and stabilizes junctional myosin. Junctional myosin depletion is similar in Cysts- and Crumbs-compromised embryos. Together, our findings indicate that Cysts is a downstream effector of the Crumbs complex and links apical polarity proteins to Rho1 and myosin activation at adherens junctions, supporting junctional integrity and epithelial polarity.
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Affiliation(s)
- Jordan T Silver
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
| | | | - Sérgio Simões
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
| | - Milena Pellikka
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
| | - Dong Yan
- Department of Genetics, Harvard Medical School, Boston, MA
| | - Richard Binari
- Department of Genetics, Harvard Medical School, Boston, MA
| | - Takashi Nishimura
- RIKEN Center for Biosystems Dynamics Research, Minatojima-minamimachi, Kobe, Japan
| | - Yan Li
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
| | - Tony J C Harris
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
| | - Norbert Perrimon
- Department of Genetics, Harvard Medical School, Boston, MA .,Howard Hughes Medical Institute, Harvard Medical School, Boston, MA
| | - Ulrich Tepass
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
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9
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A Multivariate Genome-Wide Association Study of Wing Shape in Drosophila melanogaster. Genetics 2019; 211:1429-1447. [PMID: 30792267 DOI: 10.1534/genetics.118.301342] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Accepted: 02/03/2019] [Indexed: 02/02/2023] Open
Abstract
Due to the complexity of genotype-phenotype relationships, simultaneous analyses of genomic associations with multiple traits will be more powerful and informative than a series of univariate analyses. However, in most cases, studies of genotype-phenotype relationships have been analyzed only one trait at a time. Here, we report the results of a fully integrated multivariate genome-wide association analysis of the shape of the Drosophila melanogaster wing in the Drosophila Genetic Reference Panel. Genotypic effects on wing shape were highly correlated between two different laboratories. We found 2396 significant SNPs using a 5% false discovery rate cutoff in the multivariate analyses, but just four significant SNPs in univariate analyses of scores on the first 20 principal component axes. One quarter of these initially significant SNPs retain their effects in regularized models that take into account population structure and linkage disequilibrium. A key advantage of multivariate analysis is that the direction of the estimated phenotypic effect is much more informative than a univariate one. We exploit this fact to show that the effects of knockdowns of genes implicated in the initial screen were on average more similar than expected under a null model. A subset of SNP effects were replicable in an unrelated panel of inbred lines. Association studies that take a phenomic approach, considering many traits simultaneously, are an important complement to the power of genomics.
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10
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Córdoba S, Estella C. The transcription factor Dysfusion promotes fold and joint morphogenesis through regulation of Rho1. PLoS Genet 2018; 14:e1007584. [PMID: 30080872 PMCID: PMC6095628 DOI: 10.1371/journal.pgen.1007584] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 08/16/2018] [Accepted: 07/24/2018] [Indexed: 12/22/2022] Open
Abstract
The mechanisms that control tissue patterning and cell behavior are extensively studied separately, but much less is known about how these two processes are coordinated. Here we show that the Drosophila transcription factor Dysfusion (Dysf) directs leg epithelial folding and joint formation through the regulation of Rho1 activity. We found that Dysf-induced Rho1 activity promotes apical constriction specifically in folding epithelial cells. Here we show that downregulation of Rho1 or its downstream effectors cause defects in fold and joint formation. In addition, Rho1 and its effectors are sufficient to induce the formation of epithelial folds when misexpressed in a flat epithelium. Furthermore, as apoptotic cells can actively control tissue remodeling, we analyzed the role of cell death in the formation of tarsal folds and its relation to Rho1 activity. Surprisingly, we found no defects in this process when apoptosis is inhibited. Our results highlight the coordination between a patterning transcription factor and the cellular processes that cause the cell shape changes necessary to sculpt a flat epithelium into a three dimensional structure. Epithelial morphogenesis drives the formation of organs and the acquisition of body shape. Changes in cell behavior such as cell proliferation, cell shape or apoptosis contribute to the remodeling of the epithelia from a simple layer to a three dimensional structure. These changes have to be precisely regulated by an underlying patterning network to control the final shape of an organ. However, how these two processes are coordinated is mostly unknown. In this work we use the formation of the fly leg joints as a model to study how Dysfusion (Dysf), a patterning transcription factor, regulates the cellular mechanisms that form the folds in the leg discs epithelium. We have found that dysf modulates the localization and activity of Rho1, a key regulator of the acto-myosin cytoskeleton, to drive cell apical constriction and epithelial folding in the leg disc. Furthermore, in this work we provide proof of the direct requirements of Rho1 and its downstream effectors in fold and joint formation. We conclude that Dysf-regulated Rho1 activity controls the cell shape changes that sculpt leg joints.
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Affiliation(s)
- Sergio Córdoba
- Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid (UAM)-CSIC, Madrid, Spain
| | - Carlos Estella
- Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid (UAM)-CSIC, Madrid, Spain
- * E-mail:
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11
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Segal D, Zaritsky A, Schejter ED, Shilo BZ. Feedback inhibition of actin on Rho mediates content release from large secretory vesicles. J Cell Biol 2018; 217:1815-1826. [PMID: 29496739 PMCID: PMC5940311 DOI: 10.1083/jcb.201711006] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 12/24/2017] [Accepted: 01/30/2018] [Indexed: 12/02/2022] Open
Abstract
Secretion of adhesive glycoproteins to the lumen of Drosophila melanogaster larval salivary glands is performed by contraction of an actomyosin network assembled around large secretory vesicles, after their fusion to the apical membranes. We have identified a cycle of actin coat nucleation and disassembly that is independent of myosin. Recruitment of active Rho1 to the fused vesicle triggers activation of the formin Diaphanous and actin nucleation. This leads to actin-dependent localization of a RhoGAP protein that locally shuts off Rho1, promoting disassembly of the actin coat. When contraction of vesicles is blocked, the strict temporal order of the recruited elements generates repeated oscillations of actin coat formation and disassembly. Interestingly, different blocks to actin coat disassembly arrested vesicle contraction, indicating that actin turnover is an integral part of the actomyosin contraction cycle. The capacity of F-actin to trigger a negative feedback on its own production may be widely used to coordinate a succession of morphogenetic events or maintain homeostasis.
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Affiliation(s)
- Dagan Segal
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Assaf Zaritsky
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
- Lyda Hill Department of Bioinformatics, University of Texas Southwestern Medical Center, Dallas, TX
| | - Eyal D Schejter
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
| | - Ben-Zion Shilo
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot, Israel
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12
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Couturier L, Mazouni K, Bernard F, Besson C, Reynaud E, Schweisguth F. Regulation of cortical stability by RhoGEF3 in mitotic Sensory Organ Precursor cells in Drosophila. Biol Open 2017; 6:1851-1860. [PMID: 29101098 PMCID: PMC5769646 DOI: 10.1242/bio.026641] [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] [Indexed: 11/30/2022] Open
Abstract
In epithelia, mitotic cells round up and push against their neighbors to divide. Mitotic rounding results from increased assembly of F-actin and cortical recruitment of Myosin II, leading to increased cortical stability. Whether this process is developmentally regulated is not well known. Here, we examined the regulation of cortical stability in Sensory Organ Precursor cells (SOPs) in the Drosophila pupal notum. SOPs differed in apical shape and actomyosin dynamics from their epidermal neighbors prior to division, and appeared to have a more rigid cortex at mitosis. We identified RhoGEF3 as an actin regulator expressed at higher levels in SOPs, and showed that RhoGEF3 had in vitro GTPase Exchange Factor (GEF) activity for Cdc42. Additionally, RhoGEF3 genetically interacted with both Cdc42 and Rac1 when overexpressed in the fly eye. Using a null RhoGEF3 mutation generated by CRISPR-mediated homologous recombination, we showed using live imaging that the RhoGEF3 gene, despite being dispensable for normal development, contributed to cortical stability in dividing SOPs. We therefore suggest that cortical stability is developmentally regulated in dividing SOPs of the fly notum. Summary: RhoGEF3 is a developmentally regulated Cdc42 GEF that contributes to cortical stability during asymmetric divisions of Sensory Organ Precursor cells in Drosophila.
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Affiliation(s)
- Lydie Couturier
- Institut Pasteur, Department of Developmental and Stem Cell Biology, F-75015 Paris, France.,CNRS, UMR3738, F-75015 Paris, France
| | - Khalil Mazouni
- Institut Pasteur, Department of Developmental and Stem Cell Biology, F-75015 Paris, France.,CNRS, UMR3738, F-75015 Paris, France
| | - Fred Bernard
- Institut Pasteur, Department of Developmental and Stem Cell Biology, F-75015 Paris, France.,CNRS, UMR3738, F-75015 Paris, France
| | - Charlotte Besson
- Institut Pasteur, Department of Developmental and Stem Cell Biology, F-75015 Paris, France.,CNRS, UMR3738, F-75015 Paris, France.,Université Pierre et Marie Curie, Cellule Pasteur UPMC, rue du Dr Roux, 75015 Paris, France
| | - Elodie Reynaud
- Institut Pasteur, Department of Developmental and Stem Cell Biology, F-75015 Paris, France.,CNRS, UMR3738, F-75015 Paris, France
| | - François Schweisguth
- Institut Pasteur, Department of Developmental and Stem Cell Biology, F-75015 Paris, France .,CNRS, UMR3738, F-75015 Paris, France
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13
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Kojima T. Developmental mechanism of the tarsus in insect legs. CURRENT OPINION IN INSECT SCIENCE 2017; 19:36-42. [PMID: 28521941 DOI: 10.1016/j.cois.2016.11.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2016] [Revised: 11/16/2016] [Accepted: 11/22/2016] [Indexed: 06/07/2023]
Abstract
Insects show a tremendous morphological variety and have been a subject of studying morphological evolution. In legs, the tarsus is especially variable in the number of subsegments (tarsal segments) and their proportion unlike other leg segments. Recent studies in Drosophila melanogaster have revealed details of the tarsal development: regionalization of the tarsal region through integration of regulatory network and its growth, determination of the joint-forming region in each segment through strict regulation of Notch activity, changes in tissue morphology through regulation of RhoGTPases regulators and localized cell death, and finally, the morphogenetic mechanism of the ball-and-socket joint between tarsal segments. The substantial knowledge of the tarsal development makes it a suitable model for studying mechanisms of morphological evolution and diversification.
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Affiliation(s)
- Tetsuya Kojima
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
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14
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Mason FM, Xie S, Vasquez CG, Tworoger M, Martin AC. RhoA GTPase inhibition organizes contraction during epithelial morphogenesis. J Cell Biol 2016; 214:603-17. [PMID: 27551058 PMCID: PMC5004446 DOI: 10.1083/jcb.201603077] [Citation(s) in RCA: 97] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Accepted: 07/15/2016] [Indexed: 12/05/2022] Open
Abstract
During morphogenesis, contraction of the actomyosin cytoskeleton within individual cells drives cell shape changes that fold tissues. Coordination of cytoskeletal contractility is mediated by regulating RhoA GTPase activity. Guanine nucleotide exchange factors (GEFs) activate and GTPase-activating proteins (GAPs) inhibit RhoA activity. Most studies of tissue folding, including apical constriction, have focused on how RhoA is activated by GEFs to promote cell contractility, with little investigation as to how GAPs may be important. Here, we identify a critical role for a RhoA GAP, Cumberland GAP (C-GAP), which coordinates with a RhoA GEF, RhoGEF2, to organize spatiotemporal contractility during Drosophila melanogaster apical constriction. C-GAP spatially restricts RhoA pathway activity to a central position in the apical cortex. RhoGEF2 pulses precede myosin, and C-GAP is required for pulsation, suggesting that contractile pulses result from RhoA activity cycling. Finally, C-GAP expression level influences the transition from reversible to irreversible cell shape change, which defines the onset of tissue shape change. Our data demonstrate that RhoA activity cycling and modulating the ratio of RhoGEF2 to C-GAP are required for tissue folding.
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Affiliation(s)
- Frank M Mason
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Shicong Xie
- Computational and Systems Biology, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Claudia G Vasquez
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Michael Tworoger
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Adam C Martin
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142
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15
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Suzanne M. Molecular and cellular mechanisms involved in leg joint morphogenesis. Semin Cell Dev Biol 2016; 55:131-8. [DOI: 10.1016/j.semcdb.2016.01.032] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Accepted: 01/22/2016] [Indexed: 01/09/2023]
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16
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Cilla R, Mechery V, Hernandez de Madrid B, Del Signore S, Dotu I, Hatini V. Segmentation and tracking of adherens junctions in 3D for the analysis of epithelial tissue morphogenesis. PLoS Comput Biol 2015; 11:e1004124. [PMID: 25884654 PMCID: PMC4401792 DOI: 10.1371/journal.pcbi.1004124] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Accepted: 01/12/2015] [Indexed: 11/18/2022] Open
Abstract
Epithelial morphogenesis generates the shape of tissues, organs and embryos and is fundamental for their proper function. It is a dynamic process that occurs at multiple spatial scales from macromolecular dynamics, to cell deformations, mitosis and apoptosis, to coordinated cell rearrangements that lead to global changes of tissue shape. Using time lapse imaging, it is possible to observe these events at a system level. However, to investigate morphogenetic events it is necessary to develop computational tools to extract quantitative information from the time lapse data. Toward this goal, we developed an image-based computational pipeline to preprocess, segment and track epithelial cells in 4D confocal microscopy data. The computational pipeline we developed, for the first time, detects the adherens junctions of epithelial cells in 3D, without the need to first detect cell nuclei. We accentuate and detect cell outlines in a series of steps, symbolically describe the cells and their connectivity, and employ this information to track the cells. We validated the performance of the pipeline for its ability to detect vertices and cell-cell contacts, track cells, and identify mitosis and apoptosis in surface epithelia of Drosophila imaginal discs. We demonstrate the utility of the pipeline to extract key quantitative features of cell behavior with which to elucidate the dynamics and biomechanical control of epithelial tissue morphogenesis. We have made our methods and data available as an open-source multiplatform software tool called TTT (http://github.com/morganrcu/TTT) Epithelia are the most common tissue type in multicellular organisms. Understanding processes that make them acquire their final shape has implications to pathologies such as cancer progression and birth defects such as spina bifida. During development, epithelial tissues are remodeled by mechanical forces applied at the Adherens Junctions (AJs). The AJs form a belt-like structure below the apical surface that functions to both mechanically link epithelial cells and enable cells to remodel their shape and contacts with their neighbors. In order to study epithelial morphogenesis in a quantitative and systematic way, it is necessary to measure the changes in the shape of the AJs over time. To this end we have built a complete computational pipeline to process image volumes generated by laser scanning confocal microscopy of epithelial tissues where the AJs have been marked with AJ proteins tagged with GFP. The system transforms input voxel intensity values into a symbolic description of the cells in the tissue, their connectivity and their temporal evolution, including the discovery of mitosis and apoptosis. As a proof of concept, we employed the data generated by our system to study aspects of morphogenesis of the Drosophila notum.
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Affiliation(s)
- Rodrigo Cilla
- Department of Developmental, Molecular & Chemical Biology. Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America
- * E-mail: (RC); (VH)
| | - Vinodh Mechery
- Department of Developmental, Molecular & Chemical Biology. Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America
| | - Beatriz Hernandez de Madrid
- Department of Developmental, Molecular & Chemical Biology. Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America
| | - Steven Del Signore
- Department of Developmental, Molecular & Chemical Biology. Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America
| | - Ivan Dotu
- Department of Biology, Boston College, Boston, Massachusetts, United States of America
| | - Victor Hatini
- Department of Developmental, Molecular & Chemical Biology. Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America
- * E-mail: (RC); (VH)
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17
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de Madrid BH, Greenberg L, Hatini V. RhoGAP68F controls transport of adhesion proteins in Rab4 endosomes to modulate epithelial morphogenesis of Drosophila leg discs. Dev Biol 2015; 399:283-95. [PMID: 25617722 PMCID: PMC4352398 DOI: 10.1016/j.ydbio.2015.01.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Revised: 12/15/2014] [Accepted: 01/10/2015] [Indexed: 02/06/2023]
Abstract
Elongation and invagination of epithelial tissues are fundamental developmental processes that contribute to the morphogenesis of embryonic and adult structures and are dependent on coordinated remodeling of cell-cell contacts. The morphogenesis of Drosophila leg imaginal discs depends on extensive remodeling of cell contacts and thus provides a useful system with which to investigate the underlying mechanisms. The small Rho GTPase regulator RhoGAP68F has been previously implicated in leg morphogenesis. It consists of on an N-terminal Sec14 domain and a C-terminal GAP domain. Here we examined the molecular function and role of RhoGAP68F in epithelial remodeling. We find that depletion of RhoGAP68F impairs epithelial remodeling from a pseudostratified to simple, while overexpression of RhoGAP68F causes tears of lateral cell-cell contacts and thus impairs epithelial integrity. We show that the RhoGAP68F protein localizes to Rab4 recycling endosomes and forms a complex with the Rab4 protein. The Sec14 domain is sufficient for localizing to Rab4 endosomes, while the activity of the GAP domain is dispensable. RhoGAP68F, in turn, inhibits the scission and movement of Rab4 endosomes involved in transport the adhesion proteins Fasciclin3 and E-cadherin back to cell-cell contacts. Expression of RhoGAP68F is upregulated during prepupal development suggesting that RhoGAP68F decreases the transport of key adhesion proteins to the cell surface during this developmental stage to decrease the strength of adhesive cell-cell contacts and thereby facilitate epithelial remodeling and leg morphogenesis.
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Affiliation(s)
- Beatriz Hernandez de Madrid
- Department of Developmental, Molecular and Chemical Biology, Program in Cell, Molecular and Developmental Biology, Program in Genetics, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, 150 Harrison Avenue, Boston, MA 02111, USA
| | - Lina Greenberg
- Department of Developmental, Molecular and Chemical Biology, Program in Cell, Molecular and Developmental Biology, Program in Genetics, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, 150 Harrison Avenue, Boston, MA 02111, USA
| | - Victor Hatini
- Department of Developmental, Molecular and Chemical Biology, Program in Cell, Molecular and Developmental Biology, Program in Genetics, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, 150 Harrison Avenue, Boston, MA 02111, USA.
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18
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The bHLH-PAS transcription factor dysfusion regulates tarsal joint formation in response to Notch activity during drosophila leg development. PLoS Genet 2014; 10:e1004621. [PMID: 25329825 PMCID: PMC4199481 DOI: 10.1371/journal.pgen.1004621] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 07/19/2014] [Indexed: 01/22/2023] Open
Abstract
A characteristic of all arthropods is the presence of flexible structures called joints that connect all leg segments. Drosophila legs include two types of joints: the proximal or "true" joints that are motile due to the presence of muscle attachment and the distal joints that lack musculature. These joints are not only morphologically, functionally and evolutionarily different, but also the morphogenetic program that forms them is distinct. Development of both proximal and distal joints requires Notch activity; however, it is still unknown how this pathway can control the development of such homologous although distinct structures. Here we show that the bHLH-PAS transcription factor encoded by the gene dysfusion (dys), is expressed and absolutely required for tarsal joint development while it is dispensable for proximal joints. In the presumptive tarsal joints, Dys regulates the expression of the pro-apoptotic genes reaper and head involution defective and the expression of the RhoGTPases modulators, RhoGEf2 and RhoGap71E, thus directing key morphogenetic events required for tarsal joint development. When ectopically expressed, dys is able to induce some aspects of the morphogenetic program necessary for distal joint development such as fold formation and programmed cell death. This novel Dys function depends on its obligated partner Tango to activate the transcription of target genes. We also identified a dedicated dys cis-regulatory module that regulates dys expression in the tarsal presumptive leg joints through direct Su(H) binding. All these data place dys as a key player downstream of Notch, directing distal versus proximal joint morphogenesis.
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The zinc finger homeodomain-2 gene of Drosophila controls Notch targets and regulates apoptosis in the tarsal segments. Dev Biol 2013; 385:350-65. [PMID: 24144920 DOI: 10.1016/j.ydbio.2013.10.011] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2013] [Revised: 10/06/2013] [Accepted: 10/12/2013] [Indexed: 12/19/2022]
Abstract
The development of the Drosophila leg is a good model to study processes of pattern formation, cell death and segmentation. Such processes require the coordinate activity of different genes and signaling pathways that progressively subdivide the leg territory into smaller domains. One of the main pathways needed for leg development is the Notch pathway, required for determining the proximo-distal axis of the leg and for the formation of the joints that separate different leg segments. The mechanisms required to coordinate such events are largely unknown. We describe here that the zinc finger homeodomain-2 (zfh-2) gene is highly expressed in cells that will form the leg joints and needed to establish a correct size and pattern in the distal leg. There is an early requirement of zfh-2 to establish the correct proximo-distal axis, but zfh-2 is also needed at late third instar to form the joint between the fourth and fifth tarsal segments. The expression of zfh-2 requires Notch activity but zfh-2 is necessary, in turn, to activate Notch targets such as Enhancer of split and big brain. zfh-2 is controlled by the Drosophila activator protein 2 gene and regulates the late expression of tarsal-less. In the absence of zfh-2 many cells ectopically express the pro-apoptotic gene head involution defective, activate caspase-3 and are positive for acridine orange, indicating they undergo apoptosis. Our results demonstrate the key role of zfh-2 in the control of cell death and Notch signaling during leg development.
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20
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Neisch AL, Formstecher E, Fehon RG. Conundrum, an ARHGAP18 orthologue, regulates RhoA and proliferation through interactions with Moesin. Mol Biol Cell 2013; 24:1420-33. [PMID: 23468526 PMCID: PMC3639053 DOI: 10.1091/mbc.e12-11-0800] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
RhoA, a small GTPase, regulates epithelial integrity and morphogenesis by controlling filamentous actin assembly and actomyosin contractility. Another important cytoskeletal regulator, Moesin (Moe), an ezrin, radixin, and moesin (ERM) protein, has the ability to bind to and organize cortical F-actin, as well as the ability to regulate RhoA activity. ERM proteins have previously been shown to interact with both RhoGEF (guanine nucleotide exchange factors) and RhoGAP (GTPase activating proteins), proteins that control the activation state of RhoA, but the functions of these interactions remain unclear. We demonstrate that Moe interacts with an unusual RhoGAP, Conundrum (Conu), and recruits it to the cell cortex to negatively regulate RhoA activity. In addition, we show that cortically localized Conu can promote cell proliferation and that this function requires RhoGAP activity. Surprisingly, Conu's ability to promote growth also appears dependent on increased Rac activity. Our results reveal a molecular mechanism by which ERM proteins control RhoA activity and suggest a novel linkage between the small GTPases RhoA and Rac in growth control.
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Affiliation(s)
- Amanda L Neisch
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA
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21
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Raudaskoski M, Kothe E, Fowler TJ, Jung EM, Horton JS. Ras and Rho small G proteins: insights from the Schizophyllum commune genome sequence and comparisons to other fungi. Biotechnol Genet Eng Rev 2012; 28:61-100. [PMID: 22616482 DOI: 10.5661/bger-28-61] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Unlike in animal cells and yeasts, the Ras and Rho small G proteins and their regulators have not received extensive research attention in the case of the filamentous fungi. In an effort to begin to rectify this deficiency, the genome sequence of the basidiomycete mushroom Schizophyllum commune was searched for all known components of the Ras and Rho signalling pathways. The results of this study should provide an impetus for further detailed investigations into their role in polarized hyphal growth, sexual reproduction and fruiting body development. These processes have long been the targets for genetic and cell biological research in this fungus.
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Affiliation(s)
- Marjatta Raudaskoski
- Department of Biology, University of Turku, Biocity A, Tykistökatu 6A, FI-20520 Turku, Finland
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Estella C, Voutev R, Mann RS. A dynamic network of morphogens and transcription factors patterns the fly leg. Curr Top Dev Biol 2012; 98:173-98. [PMID: 22305163 DOI: 10.1016/b978-0-12-386499-4.00007-0] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Animal appendages require a proximodistal (PD) axis, which forms orthogonally from the two main body axes, anteroposterior and dorsoventral. In this review, we discuss recent advances that begin to provide insights into the molecular mechanisms controlling PD axis formation in the Drosophila leg. In this case, two morphogens, Wingless (Wg) and Decapentaplegic (Dpp), initiate a genetic cascade that, together with growth of the leg imaginal disc, establishes the PD axis. The analysis of cis-regulatory modules (CRMs) that control the expression of genes at different positions along the PD axis has been particularly valuable in dissecting this complex process. From these experiments, it appears that only one concentration of Wg and Dpp are required to initiate PD axis formation by inducing the expression of Distal-less (Dll), a homeodomain-encoding gene that is required for leg development. Once Dll is turned on, it activates the medially expressed gene dachshund (dac). Cross-regulation between Dll and dac, together with cell proliferation in the growing leg imaginal disc, results in the formation of a rudimentary PD axis. Wg and Dpp also initiate the expression of ligands for the EGFR pathway, which in turn induces the expression of a series of target genes that pattern the distal-most portion of the leg.
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Affiliation(s)
- Carlos Estella
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, New York, USA
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Pueyo JI, Couso JP. Tarsal-less peptides control Notch signalling through the Shavenbaby transcription factor. Dev Biol 2011; 355:183-93. [PMID: 21527259 PMCID: PMC3940869 DOI: 10.1016/j.ydbio.2011.03.033] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2011] [Revised: 03/28/2011] [Accepted: 03/29/2011] [Indexed: 11/24/2022]
Abstract
The formation of signalling boundaries is one of the strategies employed by the Notch (N) pathway to give rise to two distinct signalling populations of cells. Unravelling the mechanisms involved in the regulation of these signalling boundaries is essential to understanding the role of N during development and diseases. The function of N in the segmentation of the Drosophila leg provides a good system to pursue these mechanisms at the molecular level. Transcriptional and post-transcriptional regulation of the N ligands, Serrate (Ser) and Delta (Dl) generates a signalling boundary that allows the directional activation of N in the distalmost part of the segment, the presumptive joint. A negative feedback loop between odd-skipped-related genes and the N pathway maintains this signalling boundary throughout development in the true joints. However, the mechanisms controlling N signalling boundaries in the tarsal joints are unknown. Here we show that the non-canonical tarsal-less (tal) gene (also known as pri), which encodes for four small related peptides, is expressed in the N-activated region and required for joint development in the tarsi during pupal development. This function of tal is both temporally and functionally separate from the tal-mediated tarsal intercalation during mid-third instar that we reported previously. In the pupal function described here, N signalling activates tal expression and reciprocally Tal peptides feedback on N by repressing the transcription of Dl in the tarsal joints. This Tal-induced repression of Dl is mediated by the post-transcriptional activation of the Shavenbaby transcription factor, in a similar manner as it has been recently described in the embryo. Thus, a negative feedback loop involving Tal regulates the formation and maintenance of a Dl+/Dl- boundary in the tarsal segments highlighting an ancient mechanism for the regulation of N signalling based on the action of small cell signalling peptides.
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Affiliation(s)
| | - Juan Pablo Couso
- Corresponding author: School of Life Sciences, University of Sussex, Falmer, Brighton, United Kingdom, BN1 9QG.
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