51
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Lin CM, Jiang TX, Baker RE, Maini PK, Widelitz RB, Chuong CM. Spots and stripes: pleomorphic patterning of stem cells via p-ERK-dependent cell chemotaxis shown by feather morphogenesis and mathematical simulation. Dev Biol 2009; 334:369-82. [PMID: 19647731 PMCID: PMC2811698 DOI: 10.1016/j.ydbio.2009.07.036] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2008] [Revised: 07/22/2009] [Accepted: 07/27/2009] [Indexed: 02/01/2023]
Abstract
A key issue in stem cell biology is the differentiation of homogeneous stem cells towards different fates which are also organized into desired configurations. Little is known about the mechanisms underlying the process of periodic patterning. Feather explants offer a fundamental and testable model in which multi-potential cells are organized into hexagonally arranged primordia and the spacing between primordia. Previous work explored roles of a Turing reaction-diffusion mechanism in establishing chemical patterns. Here we show that a continuum of feather patterns, ranging from stripes to spots, can be obtained when the level of p-ERK activity is adjusted with chemical inhibitors. The patterns are dose-dependent, tissue stage-dependent, and irreversible. Analyses show that ERK activity-dependent mesenchymal cell chemotaxis is essential for converting micro-signaling centers into stable feather primordia. A mathematical model based on short-range activation, long-range inhibition, and cell chemotaxis is developed and shown to simulate observed experimental results. This generic cell behavior model can be applied to model stem cell patterning behavior at large.
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Affiliation(s)
- Chih-Min Lin
- Department of Pathology, University of Southern California, Los Angeles, California 90033, USA
| | - Ting Xin Jiang
- Department of Pathology, University of Southern California, Los Angeles, California 90033, USA
| | - Ruth E. Baker
- Centre for Mathematical Biology, Mathematical Institute, University of Oxford, 24-29 St Giles', Oxford OX1 3LB, UK
| | - Philip K. Maini
- Centre for Mathematical Biology, Mathematical Institute, University of Oxford, 24-29 St Giles', Oxford OX1 3LB, UK
- Oxford Centre for Integrative Systems Biology, Department for Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK
| | - Randall B. Widelitz
- Department of Pathology, University of Southern California, Los Angeles, California 90033, USA
| | - Cheng-Ming Chuong
- Department of Pathology, University of Southern California, Los Angeles, California 90033, USA
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52
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Andrew DJ, Ewald AJ. Morphogenesis of epithelial tubes: Insights into tube formation, elongation, and elaboration. Dev Biol 2009; 341:34-55. [PMID: 19778532 DOI: 10.1016/j.ydbio.2009.09.024] [Citation(s) in RCA: 255] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2009] [Revised: 09/16/2009] [Accepted: 09/16/2009] [Indexed: 12/17/2022]
Abstract
Epithelial tubes are a fundamental tissue across the metazoan phyla and provide an essential functional component of many of the major organs. Recent work in flies and mammals has begun to elucidate the cellular mechanisms driving the formation, elongation, and branching morphogenesis of epithelial tubes during development. Both forward and reverse genetic techniques have begun to identify critical molecular regulators for these processes and have revealed the conserved role of key pathways in regulating the growth and elaboration of tubular networks. In this review, we discuss the developmental programs driving the formation of branched epithelial networks, with specific emphasis on the trachea and salivary gland of Drosophila melanogaster and the mammalian lung, mammary gland, kidney, and salivary gland. We both highlight similarities in the development of these organs and attempt to identify tissue and organism specific strategies. Finally, we briefly consider how our understanding of the regulation of proliferation, apicobasal polarity, and epithelial motility during branching morphogenesis can be applied to understand the pathologic dysregulation of these same processes during metastatic cancer progression.
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Affiliation(s)
- Deborah J Andrew
- Department of Cell Biology and Center for Cell Dynamics, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
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53
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Mori H, Gjorevski N, Inman JL, Bissell MJ, Nelson CM. Self-organization of engineered epithelial tubules by differential cellular motility. Proc Natl Acad Sci U S A 2009; 106:14890-5. [PMID: 19706461 PMCID: PMC2736456 DOI: 10.1073/pnas.0901269106] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2009] [Indexed: 02/06/2023] Open
Abstract
Patterning of developing tissues arises from a number of mechanisms, including cell shape change, cell proliferation, and cell sorting from differential cohesion or tension. Here, we reveal that differences in cell motility can also lead to cell sorting within tissues. Using mosaic engineered mammary epithelial tubules, we found that cells sorted depending on their expression level of the membrane-anchored collagenase matrix metalloproteinase (MMP)-14. These rearrangements were independent of the catalytic activity of MMP14 but absolutely required the hemopexin domain. We describe a signaling cascade downstream of MMP14 through Rho kinase that allows cells to sort within the model tissues. Cell speed and persistence time were enhanced by MMP14 expression, but only the latter motility parameter was required for sorting. These results indicate that differential directional persistence can give rise to patterns within model developing tissues.
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Affiliation(s)
- Hidetoshi Mori
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; and
| | - Nikolce Gjorevski
- Departments of Chemical Engineering and Molecular Biology, Princeton University, Princeton, NJ 08544
| | - Jamie L. Inman
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; and
| | - Mina J. Bissell
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; and
| | - Celeste M. Nelson
- Departments of Chemical Engineering and Molecular Biology, Princeton University, Princeton, NJ 08544
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54
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Identification of receptor-tyrosine-kinase-signaling target genes reveals receptor-specific activities and pathway branchpoints during Drosophila development. Genetics 2009; 181:1335-45. [PMID: 19189950 DOI: 10.1534/genetics.108.098475] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Receptor tyrosine kinases (RTKs) are an important family of signaling molecules with the unusual property that they are able to transduce their signals using the same downstream pathways. This has led to an unresolved debate as to whether individual receptors are interchangeable, or if each receptor can mediate specific downstream responses. To address this question, we have conducted a screen to identify target genes whose expression is differentially modulated by RTKs and their downstream pathway components. Using whole-mount in situ hybridization in Drosophila embryos exposed to constitutively active RTK pathway signaling, along with quantitative RT-PCR, we found that a significant fraction of target genes respond differentially in a spatial and/or quantitative manner. This includes differential responses to EGF receptor vs. fibroblast growth factor receptor signaling as well as to more downstream components such as Ras1 and pointed. We show that not only genes but also individual alternative transcripts can respond differently to signaling, and we present evidence that the differential responses can be mediated at the transcriptional level. Our results demonstrate that different RTKs can elicit distinct transcriptional responses, and the target genes obtained from our screen provide a valuable resource for further exploration of the mechanisms underlying this signaling specificity.
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55
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Lu P, Ewald AJ, Martin GR, Werb Z. Genetic mosaic analysis reveals FGF receptor 2 function in terminal end buds during mammary gland branching morphogenesis. Dev Biol 2008; 321:77-87. [PMID: 18585375 PMCID: PMC2582391 DOI: 10.1016/j.ydbio.2008.06.005] [Citation(s) in RCA: 136] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2008] [Revised: 05/30/2008] [Accepted: 06/02/2008] [Indexed: 01/05/2023]
Abstract
FGF signaling is associated with breast cancer and is required for mammary placode formation in the mouse. In this study, we employed a genetic mosaic analysis based on Cre-mediated recombination to investigate FGF receptor 2 (Fgfr2) function in the postnatal mammary gland. Mosaic inactivation of Fgfr2 by the MMTV-Cre transgene enabled us to compare the behavior of Fgfr2 null and Fgfr2 heterozygous cells in the same gland. Fgfr2 null cells were at a competitive disadvantage to their Fgfr2 heterozygous neighbors in the highly proliferative terminal end buds (TEBs) at the invasion front, owing to a negative effect of loss of Fgfr2 function on cell proliferation. However, Fgfr2 null cells were tolerated in mature ducts. In these genetic mosaic mammary glands, the epithelial network is apparently built by TEBs that over time are composed of a progressively larger proportion of Fgfr2-positive cells. However, subsequently, most cells lose Fgfr2 function, presumably due to additional rounds of Cre-mediated recombination. Using an independent strategy to create mosaic mammary glands, which employed an adenovirus-Cre that acts only once, we confirmed that Fgfr2 null cells were out-competed by neighboring Fgfr2 heterozygous cells. Together, our data demonstrate that Fgfr2 functions in the proliferating and invading TEBs, but it is not required in the mature ducts of the pubertal mammary gland.
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Affiliation(s)
- Pengfei Lu
- Department of Anatomy and Program in Developmental Biology, University of California at San Francisco, San Francisco, CA 94143-0452, USA
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56
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Weaver M, Krasnow MA. Dual origin of tissue-specific progenitor cells in Drosophila tracheal remodeling. Science 2008; 321:1496-9. [PMID: 18669822 DOI: 10.1126/science.1158712] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
During Drosophila metamorphosis, most larval cells die. Pupal and adult tissues form from imaginal cells, tissue-specific progenitors allocated in embryogenesis that remain quiescent during embryonic and larval life. Clonal analysis and fate mapping of single, identified cells show that tracheal system remodeling at metamorphosis involves a classical imaginal cell population and a population of differentiated, functional larval tracheal cells that reenter the cell cycle and regain developmental potency. In late larvae, both populations are activated and proliferate, spread over and replace old branches, and diversify into various stalk and coiled tracheolar cells under control of fibroblast growth factor signaling. Thus, Drosophila pupal/adult tissue progenitors can arise both by early allocation of multipotent cells and late return of differentiated cells to a multipotent state, even within a single tissue.
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Affiliation(s)
- Molly Weaver
- Howard Hughes Medical Institute and Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305-5307, USA
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57
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Organ renewal and cell divisions by differentiated cells in Drosophila. Proc Natl Acad Sci U S A 2008; 105:10832-6. [PMID: 18664581 DOI: 10.1073/pnas.0805111105] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
For many organs, the processes of renewal and regeneration recruit stem cells to replace differentiated, postmitotic cells, but the capacity of an organ's differentiated cells to divide and contribute is uncertain. Most cells of the Drosophila adult are the descendants of dedicated precursors that divide and replace larval cells that are histolyzed during metamorphosis. We investigated the provenance of cells that reconstitute the second thoracic metamere of the tracheal system (Tr2). These cells contribute the precursors for Branchless(FGF)-dependent growth of the dorsal air sacs, the major tracheal organs of the adult fly. We found that, in contrast to the cells in other tracheal metameres that proceed through many cycles of endoreplication, the cells that constitute the Tr2 branches in young larvae do not. Like the cells in other tracheal metameres, these cells arrest mitotic cycling in the embryo and form differentiated, air-filled tracheal branches of the larva. We report here that they reinitiate cell divisions during the third instar (L3) to increase the Tr2 population by approximately 10-fold with multipotent cells.
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58
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Lecaudey V, Cakan-Akdogan G, Norton WHJ, Gilmour D. Dynamic Fgf signaling couples morphogenesis and migration in the zebrafish lateral line primordium. Development 2008; 135:2695-705. [PMID: 18599504 DOI: 10.1242/dev.025981] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The collective migration of cells in the form of cohesive tissues is a hallmark of both morphogenesis and repair. The extrinsic cues that direct these complex migrations usually act by regulating the dynamics of a specific subset of cells, those at the leading edge. Given that normally the function of tissue migration is to lay down multicellular structures, such as branched epithelial networks or sensory organs, it is surprising how little is known about the mechanisms that organize cells behind the leading edge. Cells of the zebrafish lateral line primordium switch from mesenchyme-like leader cells to epithelial rosettes that develop into mechanosensory organs. Here, we show that this transition is regulated by an Fgf signaling circuit that is active within the migrating primordium. Point sources of Fgf ligand drive surrounding cells towards a ;non-leader' fate by increasing their epithelial character, a prerequisite for rosette formation. We demonstrate that the dynamic expression of Fgf ligands determines the spatiotemporal pattern of epithelialization underlying sensory organ formation in the lateral line. Furthermore, this work uncovers a surprising link between internal tissue organization and collective migration.
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Affiliation(s)
- Virginie Lecaudey
- European Molecular Biology Laboratory, Meyerhofstrasse 1, Heidelberg, Germany
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59
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Affolter M, Caussinus E. Tracheal branching morphogenesis in Drosophila: new insights into cell behaviour and organ architecture. Development 2008; 135:2055-64. [PMID: 18480161 DOI: 10.1242/dev.014498] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Our understanding of the molecular control of morphological processes has increased tremendously over recent years through the development and use of high resolution in vivo imaging approaches, which have enabled cell behaviour to be linked to molecular functions. Here we review how such approaches have furthered our understanding of tracheal branching morphogenesis in Drosophila, during which the control of cell invagination, migration, competition and rearrangement is accompanied by the sequential secretion and resorption of proteins into the apical luminal space, a vital step in the elaboration of the trachea's complex tubular network. We also discuss the similarities and differences between flies and vertebrates in branched organ formation that are becoming apparent from these studies.
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Affiliation(s)
- Markus Affolter
- Biozentrum der Universität Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
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60
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Sato M, Kitada Y, Tabata T. Larval cells become imaginal cells under the control of homothorax prior to metamorphosis in the Drosophila tracheal system. Dev Biol 2008; 318:247-57. [PMID: 18455715 DOI: 10.1016/j.ydbio.2008.03.025] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2007] [Revised: 03/11/2008] [Accepted: 03/11/2008] [Indexed: 11/24/2022]
Abstract
In Drosophila melanogaster, one of the most derived species among holometabolous insects, undifferentiated imaginal cells that are set-aside during larval development are thought to proliferate and replace terminally differentiated larval cells to constitute adult structures. Essentially all tissues that undergo extensive proliferation and drastic morphological changes during metamorphosis are thought to derive from these imaginal cells and not from differentiated larval cells. The results of studies on metamorphosis of the Drosophila tracheal system suggested that large larval tracheal cells that are thought to be terminally differentiated may be eliminated via apoptosis and rapidly replaced by small imaginal cells that go on to form the adult tracheal system. However, the origin of the small imaginal tracheal cells has not been clear. Here, we show that large larval cells in tracheal metamere 2 (Tr2) divide and produce small imaginal cells prior to metamorphosis. In the absence of homothorax gene activity, larval cells in Tr2 become non-proliferative and small imaginal cells are not produced, indicating that homothorax is necessary for proliferation of Tr2 larval cells. These unexpected results suggest that larval cells can become imaginal cells and directly contribute to the adult tissue in the Drosophila tracheal system. During metamorphosis of less derived species of holometabolous insects, adult structures are known to be formed via cells constituting larval structures. Thus, the Drosophila tracheal system may utilize ancestral mode of metamorphosis.
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Affiliation(s)
- Makoto Sato
- Laboratory of Morphogenesis, Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-0032, Japan.
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61
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Mortimer NT, Moberg KH. The Drosophila F-box protein Archipelago controls levels of the Trachealess transcription factor in the embryonic tracheal system. Dev Biol 2007; 312:560-71. [PMID: 17976568 PMCID: PMC2170523 DOI: 10.1016/j.ydbio.2007.10.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Revised: 10/01/2007] [Accepted: 10/01/2007] [Indexed: 10/22/2022]
Abstract
The archipelago gene (ago) encodes the F-box specificity subunit of an SCF(skp-cullin-f box) ubiquitin ligase that inhibits cell proliferation in Drosophila melanogaster and suppresses tumorigenesis in mammals. ago limits mitotic activity by targeting cell cycle and cell growth proteins for ubiquitin-dependent degradation, but the diverse developmental roles of other F-box proteins suggests that it is likely to have additional protein targets. Here we show that ago is required for the post-mitotic shaping of the Drosophila embryonic tracheal system, and that it acts in this tissue by targeting the Trachealess (Trh) protein, a conserved bHLH-PAS transcription factor. ago restricts Trh levels in vivo and antagonizes transcription of the breathless FGF receptor, a known target of Trh in the tracheal system. At a molecular level, the Ago protein binds Trh and is required for proteasome-dependent elimination of Trh in response to expression of the Dysfusion protein. ago mutations that elevate Trh levels in vivo are defective in binding forms of Trh found in Dysfusion-positive cells. These data identify a novel function for the ago ubiquitin-ligase in tracheal morphogenesis via Trh and its target breathless, and suggest that ago has distinct functions in mitotic and post-mitotic cells that influence its role in development and disease.
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62
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Yan D, Lin X. Drosophila glypican Dally-like acts in FGF-receiving cells to modulate FGF signaling during tracheal morphogenesis. Dev Biol 2007; 312:203-16. [PMID: 17959166 PMCID: PMC2151973 DOI: 10.1016/j.ydbio.2007.09.015] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2007] [Revised: 09/09/2007] [Accepted: 09/12/2007] [Indexed: 11/23/2022]
Abstract
Previous studies in Drosophila have shown that heparan sulfate proteoglycans (HSPGs) are involved in both breathless (btl)- and heartless (htl)-mediated FGF signaling during embryogenesis. However, the mechanism(s) by which HSPGs control Btl and Htl signaling is unknown. Here we show that dally-like (dlp, a Drosophila glypican) mutant embryos exhibit severe defects in tracheal morphogenesis and show a reduction in btl-mediated FGF signaling activity. However, htl-dependent mesodermal cell migration is not affected in dlp mutant embryos. Furthermore, expression of Dlp, but not other Drosophila HSPGs, can restore effectively the tracheal morphogenesis in dlp embryos. Rescue experiments in dlp embryos demonstrate that Dlp functions only in Bnl/FGF receiving cells in a cell-autonomous manner, but is not essential for Bnl/FGF expression cells. To further dissect the mechanism(s) of Dlp in Btl signaling, we analyzed the role of Dlp in Btl-mediated air sac tracheoblast formation in wing discs. Mosaic analysis experiments show that removal of HSPG activity in FGF-producing or other surrounding cells does not affect tracheoblasts migration, while HSPG mutant tracheoblast cells fail to receive FGF signaling. Together, our results argue strongly that HSPGs regulate Btl signaling exclusively in FGF-receiving cells as co-receptors, but are not essential for the secretion and distribution of the FGF ligand. This mechanism is distinct from HSPG functions in morphogen distribution, and is likely a general paradigm for HSPG functions in FGF signaling in Drosophila.
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Affiliation(s)
- Dong Yan
- Division of Developmental Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA
- The Graduate Program in Molecular and Developmental Biology, University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA
| | - Xinhua Lin
- Division of Developmental Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229, USA
- The Graduate Program in Molecular and Developmental Biology, University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA
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63
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Rørth P. Collective guidance of collective cell migration. Trends Cell Biol 2007; 17:575-9. [PMID: 17996447 DOI: 10.1016/j.tcb.2007.09.007] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2007] [Revised: 09/17/2007] [Accepted: 09/17/2007] [Indexed: 12/12/2022]
Abstract
Some cells migrate and find their way as solitary entities. However, during development of multicellular animals and possibly during tumor dissemination, cells often move as groups, associated tightly or loosely. Recent advances in live imaging have aided examination of such 'multicellular cell biology'. Here, I propose a model for how a group of cells can process and react to guidance information as a unit rather than as a gathering of solitary cells. Signaling pathways and regulatory mechanisms can differ substantially between solitary- and collective-guidance modes; a major difference being that, in collective guidance, similar to in bacterial chemotaxis, the signal need not be localized subcellularly within the responding cell. I suggest that collective-guidance signaling occurs alongside individual cell reactions. Both produce directional migration.
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Affiliation(s)
- Pernille Rørth
- Temasek Life Sciences Laboratory (TLL), 1 Research link, National University of Singapore, 117604, Singapore.
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64
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Valentin G, Haas P, Gilmour D. The chemokine SDF1a coordinates tissue migration through the spatially restricted activation of Cxcr7 and Cxcr4b. Curr Biol 2007; 17:1026-31. [PMID: 17570670 DOI: 10.1016/j.cub.2007.05.020] [Citation(s) in RCA: 242] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2007] [Revised: 05/03/2007] [Accepted: 05/04/2007] [Indexed: 11/17/2022]
Abstract
Tissue migration is a collective behavior that plays a key role in the formation of many organ systems. Although tissue movements are guided by extrinsic cues, in many contexts, their receptors need to be active only at the leading edge to ensure morphogenesis. This has led to the prevalent view that extrinsic signals exert their influence by controlling a small number of leader cells. The zebrafish lateral-line primordium is a cohesive cohort of over 100 cells that is guided through CXCR4-SDF1 signaling. Recent work has shown that Cxcr4b activity is only required in cells at the very tip, raising the question of what controls cell behavior within trailing regions. Here, we present the first mutant in zebrafish SDF1a/CXCL12a and show, surprisingly, that the resultant phenotype is stronger than a null mutation in its cognate receptor, Cxcr4b, indicating the involvement of other SDF1a receptors. A candidate approach identified Cxcr7/RDC1, whose expression is restricted to cells behind the leading edge. Morpholino knockdown of Cxcr7 leads to a novel phenotype in which the migration of trailing cells is specifically affected, causing tissue stretching, a defect rescued by the reintroduction of wild-type cells specifically at the back of the primordium. Finally, we present evidence that Cxcr4b and Cxcr7 act independently to regulate group migration. We provide the first example where a single extrinsic guidance cue, SDF1a, directly controls the migration of both leading and trailing edges of a tissue through the activation of two independent receptors, CXCR4b and CXCR7.
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Affiliation(s)
- Guillaume Valentin
- European Molecular Biology Laboratory, Meyerhofstrasse 1, Heidelberg 69117, Germany
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65
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Kornberg TB, Guha A. Understanding morphogen gradients: a problem of dispersion and containment. Curr Opin Genet Dev 2007; 17:264-71. [PMID: 17643982 PMCID: PMC1993832 DOI: 10.1016/j.gde.2007.05.010] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2007] [Revised: 05/22/2007] [Accepted: 05/31/2007] [Indexed: 12/24/2022]
Abstract
Protein morphogens are instructive signals that regulate growth and patterning of tissues and organs. They form long-range, dynamic gradients by moving from regions of high concentration (producing cells) to regions of low concentration (the adjacent, nonproducing developmental field). Since morphogen activity must be limited to the adjacent target field, we want to understand both how signaling proteins move and how their dispersion is restricted. We consider the variety of settings for long-range morphogen systems in Drosophila. In the early embryo, morphogens appear to disperse by free diffusion, and impermeable membranes physically constrain them. However, at later stages, containment is achieved without physical barriers. We argue that in the absence of constraining barriers, gradient-generating dispersion of morphogens cannot be achieved by passive diffusion and that other mechanisms for distribution must be considered.
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Affiliation(s)
- Thomas B Kornberg
- Department of Biochemistry & Biophysics, University of California, San Francisco, CA 94158, United States.
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66
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Baer MM, Bilstein A, Leptin M. A clonal genetic screen for mutants causing defects in larval tracheal morphogenesis in Drosophila. Genetics 2007; 176:2279-91. [PMID: 17603107 PMCID: PMC1950631 DOI: 10.1534/genetics.107.074088] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The initial establishment of the tracheal network in the Drosophila embryo is beginning to be understood in great detail, both in its genetic control cascades and in its cell biological events. By contrast, the vast expansion of the system during larval growth, with its extensive ramification of preexisting tracheal branches, has been analyzed less well. The mutant phenotypes of many genes involved in this process are probably not easy to reveal, as these genes may be required for other functions at earlier developmental stages. We therefore conducted a screen for defects in individual clonal homozygous mutant cells in the tracheal network of heterozygous larvae using the mosaic analysis with a repressible cell marker (MARCM) system to generate marked, recombinant mitotic clones. We describe the identification of a set of mutants with distinct phenotypic effects. In particular we found a range of defects in terminal cells, including failure in lumen formation and reduced or extensive branching. Other mutations affect cell growth, cell shape, and cell migration.
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Affiliation(s)
- Magdalena M Baer
- Institute of Genetics, University of Cologne, Zülpicher Strasse 47, D-50674 Cologne, Germany
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67
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Chanut-Delalande H, Jung AC, Lin L, Baer MM, Bilstein A, Cabernard C, Leptin M, Affolter M. A genetic mosaic analysis with a repressible cell marker screen to identify genes involved in tracheal cell migration during Drosophila air sac morphogenesis. Genetics 2007; 176:2177-87. [PMID: 17603108 PMCID: PMC1950623 DOI: 10.1534/genetics.107.073890] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Branching morphogenesis of the Drosophila tracheal system relies on the fibroblast growth factor receptor (FGFR) signaling pathway. The Drosophila FGF ligand Branchless (Bnl) and the FGFR Breathless (Btl/FGFR) are required for cell migration during the establishment of the interconnected network of tracheal tubes. However, due to an important maternal contribution of members of the FGFR pathway in the oocyte, a thorough genetic dissection of the role of components of the FGFR signaling cascade in tracheal cell migration is impossible in the embryo. To bypass this shortcoming, we studied tracheal cell migration in the dorsal air sac primordium, a structure that forms during late larval development. Using a mosaic analysis with a repressible cell marker (MARCM) clone approach in mosaic animals, combined with an ethyl methanesulfonate (EMS)-mutagenesis screen of the left arm of the second chromosome, we identified novel genes implicated in cell migration. We screened 1123 mutagenized lines and identified 47 lines displaying tracheal cell migration defects in the air sac primordium. Using complementation analyses based on lethality, mutations in 20 of these lines were genetically mapped to specific genomic areas. Three of the mutants were mapped to either the Mhc or the stam complementation groups. Further experiments confirmed that these genes are required for cell migration in the tracheal air sac primordium.
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68
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Fata JE, Mori H, Ewald AJ, Zhang H, Yao E, Werb Z, Bissell MJ. The MAPK(ERK-1,2) pathway integrates distinct and antagonistic signals from TGFalpha and FGF7 in morphogenesis of mouse mammary epithelium. Dev Biol 2007; 306:193-207. [PMID: 17448457 PMCID: PMC2763137 DOI: 10.1016/j.ydbio.2007.03.013] [Citation(s) in RCA: 151] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2006] [Revised: 03/09/2007] [Accepted: 03/09/2007] [Indexed: 01/26/2023]
Abstract
Transforming growth factor-alpha (TGFalpha) and fibroblast growth factor-7 (FGF7) exhibit distinct expression patterns in the mammary gland. Both factors signal through mitogen-activated kinase/extracellular regulated kinase-1,2 (MAPK(ERK1,2)); however, their unique and/or combined contributions to mammary morphogenesis have not been examined. In ex vivo mammary explants, we show that a sustained activation of MAPK(ERK1,2) for 1 h, induced by TGFalpha, was necessary and sufficient to initiate branching morphogenesis, whereas a transient activation (15 min) of MAPK(ERK1,2), induced by FGF7, led to growth without branching. Unlike TGFalpha, FGF7 promoted sustained proliferation as well as ectopic localization of, and increase in, keratin-6 expressing cells. The response of the explants to FGF10 was similar to that to FGF7. Simultaneous stimulation by FGF7 and TGFalpha indicated that the FGF7-induced MAPK(ERK1,2) signaling and associated phenotypes were dominant: FGF7 may prevent branching by suppression of two necessary TGFalpha-induced morphogenetic effectors, matrix metalloproteinase-3 (MMP-3/stromelysin-1), and fibronectin. Our findings indicate that expression of morphogenetic effectors, proliferation, and cell-type decisions during mammary organoid morphogenesis are intimately dependent on the duration of activation of MAPK(ERK1,2) activation.
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Affiliation(s)
- Jimmie E. Fata
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Hidetoshi Mori
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Andrew J. Ewald
- Department of Anatomy, University of California, San Francisco, CA 94143, USA
| | - Hui Zhang
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Evelyn Yao
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Zena Werb
- Department of Anatomy, University of California, San Francisco, CA 94143, USA
| | - Mina J. Bissell
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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69
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Abstract
The RAS-RAF-MEK-extracellular-regulated kinase (RAS/ERK) pathway is a major intracellular route used by metazoan cells to channel to downstream targets a diverse array of signals, including those controlling cell proliferation and survival. Recent findings suggest that the pathway is assembled by specific scaffolding proteins that in turn regulate the efficiency, the location and/or the duration of signal transmission. Here, through the angle of studies conducted in Drosophila and C. elegans, we present two such proteins, the kinase suppressor of RAS (KSR) and connector enhancer of KSR (CNK) scaffolds, and highlight their implication in a novel mechanism regulating RAS-mediated RAF activation. Based on recent findings, we discuss the possibility that KSR, a RAF-like protein, does not solely act as a scaffold, but directly induces RAF catalytic function by a kinase-independent mechanism apparently shared by RAF-like proteins.
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Affiliation(s)
- A Clapéron
- Institute for Research in Immunology and Cancer, Laboratory of Intracellular Signaling, Université de Montréal CP, Montréal, Québec, Canada
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70
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Shaw AT, Meissner A, Dowdle JA, Crowley D, Magendantz M, Ouyang C, Parisi T, Rajagopal J, Blank LJ, Bronson RT, Stone JR, Tuveson DA, Jaenisch R, Jacks T. Sprouty-2 regulates oncogenic K-ras in lung development and tumorigenesis. Genes Dev 2007; 21:694-707. [PMID: 17369402 PMCID: PMC1820943 DOI: 10.1101/gad.1526207] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Somatic activation of Ras occurs frequently in human cancers, including one-third of lung cancers. Activating Ras mutations also occur in the germline, leading to complex developmental syndromes. The precise mechanism by which Ras activation results in human disease is uncertain. Here we describe the phenotype of a mouse engineered to harbor a germline oncogenic K-rasG12D mutation. This mouse exhibits early embryonic lethality due to a placental trophoblast defect. Reconstitution with a wild-type placenta rescues the early lethality, but mutant embryos still succumb to cardiovascular and hematopoietic defects. In addition, mutant embryos demonstrate a profound defect in lung branching morphogenesis associated with striking up-regulation of the Ras/mitogen-activated protein kinase (MAPK) antagonist Sprouty-2 and abnormal localization of MAPK activity within the lung epithelium. This defect can be significantly suppressed by lentiviral short hairpin RNA (shRNA)-mediated knockdown of Sprouty-2 in vivo. Furthermore, in the context of K-rasG12D-mediated lung tumorigenesis, Sprouty-2 is also up-regulated and functions as a tumor suppressor to limit tumor number and overall tumor burden. These findings indicate that in the lung, Sprouty-2 plays a critical role in the regulation of oncogenic K-ras, and implicate counter-regulatory mechanisms in the pathogenesis of Ras-based disease.
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Affiliation(s)
- Alice T. Shaw
- Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Massachusetts General Hospital Cancer Center and Harvard Medical School, Boston, Massachusetts 02114, USA
| | - Alexander Meissner
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA
| | - James A. Dowdle
- Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Denise Crowley
- Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Howard Hughes Medical Institute at Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Margaret Magendantz
- Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Chensi Ouyang
- Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Tiziana Parisi
- Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Jayaraj Rajagopal
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Leah J. Blank
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Roderick T. Bronson
- Department of Pathology, Tufts University School of Medicine and Veterinary Medicine, Boston, Massachusetts 02111, USA
| | - James R. Stone
- Department of Pathology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
| | | | - Rudolf Jaenisch
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA
| | - Tyler Jacks
- Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Howard Hughes Medical Institute at Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Corresponding author.E-MAIL ; FAX (617) 253-9863
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71
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Abstract
Endothelial cell migration is essential to angiogenesis. This motile process is directionally regulated by chemotactic, haptotactic, and mechanotactic stimuli and further involves degradation of the extracellular matrix to enable progression of the migrating cells. It requires the activation of several signaling pathways that converge on cytoskeletal remodeling. Then, it follows a series of events in which the endothelial cells extend, contract, and throw their rear toward the front and progress forward. The aim of this review is to give an integrative view of the signaling mechanisms that govern endothelial cell migration in the context of angiogenesis.
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Affiliation(s)
- Laurent Lamalice
- Le Centre de recherche en cancérologie, l'Université Laval, L'Hôtel-Dieu de Québec, Québec, Canada
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72
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Abstract
Wnt signaling cascades activate morphogenetic programs that range from cell migration and proliferation to cell fate determination and stem cell renewal. These pathways enable cells to translate environmental cues into the complex cellular programs that are needed to organize tissues and build organs. Wnt signaling is essential for renal development; however, the specific molecular underpinnings involved are poorly understood. Recent research has revealed an unexpected intersection between Wnt signaling and polycystic kidney disease. Some polycystic kidney disease proteins, such as Inversin and Bardet-Biedl syndrome family members, were found to use components of the Wnt signaling cascade to orient cells along a secondary polarity axis within the plane of the epithelium. These spatial cues may be needed to position nascent tubules with a defined geometry.
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Affiliation(s)
- Thomas Benzing
- Renal Division, University Hospital Freiburg, Freiburg, Germany
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73
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Kuslak SL, Marker PC. Fibroblast growth factor receptor signaling through MEK-ERK is required for prostate bud induction. Differentiation 2007; 75:638-51. [PMID: 17309601 DOI: 10.1111/j.1432-0436.2006.00161.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The urogenital sinus (UGS) is specified as prostate in mice around embryonic day 15.5 as indicated by expression of the transcription factor Nkx3.1. Shortly thereafter, growth of epithelial buds into the UGS mesenchyme initiates prostatic morphogenesis. A comparison of male and female UGSs in vivo demonstrated sexually dimorphic expression of branching morphogenesis regulatory genes coincident with epithelial budding including Bmp7, Gli1, Gli2, Fgf10, Ptch1, and Shh. A comparison of UGSs grown with or without testosterone in serum-free organ cultures showed that some, but not all sexually dimorphic differences observed during prostate bud induction, were effectively modeled in vitro. Organ cultures were then used to investigate the role of fibroblast growth factor receptor (FGFR) signaling during prostatic induction. Blocking FGFR activation with PD173074 showed that activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in the UGS is dependent on FGFR signaling. Furthermore, inhibiting either FGFR activation with PD173074 or ERK1/2 activation with UO126 blocked all morphogenesis, proliferation, and gene expression changes induced by androgens in the UGS. These data reveal a previously unknown role for ERK1/2 during prostate bud induction. They also show that signaling by FGFRs through ERK1/2 is required for androgen-induced budding morphogenesis, proliferation, and gene expression during prostate bud induction.
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Affiliation(s)
- Sheri L Kuslak
- Department of Genetics, Cell Biology and Development, University of Minnesota Comprehensive Cancer Center, University of Minnesota, 420 Delaware St. SE, Minneapolis, MN 55455, USA
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74
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Iizuka M, Sasaki K, Hirai Y, Shindo K, Konno S, Itou H, Ohshima S, Horie Y, Watanabe S. Morphogenic protein epimorphin protects intestinal epithelial cells from oxidative stress by the activation of EGF receptor and MEK/ERK, PI3 kinase/Akt signals. Am J Physiol Gastrointest Liver Physiol 2007; 292:G39-G52. [PMID: 16891298 DOI: 10.1152/ajpgi.00181.2006] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Epimorphin is a mesenchymal protein that regulates morphogenesis of epithelial cells. Our preliminary study suggested a novel function of epimorphin in enhancing survival of intestinal epithelial cells (IEC). Oxidative stress leads to cell injury and death and is suggested to be a key contributor to pathogenesis of inflammatory bowel disease. This study was conducted to determine whether epimorphin protects IEC from oxidative stress. Rat intestinal epithelial cell line IEC-6 was cultured with epimorphin (10 and 20 mug/ml), and the life span of IEC was assessed. The mean life span of IEC-6 cells was prolonged 1.9-fold (P < 0.0006) by treatment with epimorphin. We then examined the epimorphin signaling pathways. Epimorphin phosphorylated epidermal growth factor (EGF) receptor, activated the MEK/extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase and phosphatidylinositol 3 (PI3) kinase/Akt pathways, phosphorylated Bad, and induced Bcl-X(L) and survivin. Hydrogen peroxide (1 mM) induced cell death in 92% of IEC-6 cells, but epimorphin dramatically diminished (88.7%) cell death induced by hydrogen peroxide (P < 0.0001). This protective effect of epimorphin was significantly attenuated by inhibitors of MEK and PI3 kinase (P < 0.0001) or EGF receptor-neutralizing antibody (P = 0.0007). In wound assays, the number of migrated cells in the wound area decreased (72.5%) by treatment with 30 muM hydrogen peroxide, but epimorphin increased the number of migrated cells 3.18-fold (P < 0.0001). These results support a novel function of epimorphin in protecting IEC from oxidative stress. This anti-oxidative function of epimorphin is dramatic and is likely mediated by the activation of EGF receptors and the MEK/extracellular signal-regulated kinase and PI3 kinase/Akt signaling pathways and through the induction of anti-apoptotic factors.
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Affiliation(s)
- Masahiro Iizuka
- Department of Internal Medicine, Akita University School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan.
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75
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Abstract
The ureteric bud (UB) is an outgrowth of the Wolffian duct, which undergoes a complex process of growth, branching, and remodeling, to eventually give rise to the entire urinary collecting system during kidney development. Understanding the mechanisms that control this process is a fascinating problem in basic developmental biology, and also has considerable medical significance. Over the past decade, there has been significant progress in our understanding of renal branching morphogenesis and its regulation, and this review focuses on several areas in which there have been recent advances. The first section deals with the normal process of UB branching morphogenesis, and methods that have been developed to better observe and describe it. The next section discusses a number of experimental methodologies, both established and novel, that make kidney development in the mouse a powerful and attractive experimental system. The third section discusses some of the cellular processes that are likely to underlie UB branching morphogenesis, as well as recent data on cell lineages within the growing UB. The fourth section summarizes our understanding of the roles of two groups of growth factors that appear to be particularly important for the regulation of UB outgrowth and branching: GDNF and FGFs, which stimulate this process via tyrosine kinase receptors, and members of the TGFbeta family, including BMP4 and Activin A, which generally inhibit UB formation and branching.
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Affiliation(s)
- Frank Costantini
- Department of Genetics and Development, Columbia University Medical Center, 701 W. 168th St. New York, NY 10032, USA.
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76
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Abstract
Much progress has been made in recent years toward understanding mechanisms controlling branching morphogenesis, a fundamental aspect of development in a variety of invertebrate and vertebrate organs. To gain a deeper understanding of how branching morphogenesis occurs in the mammary gland, we compare and contrast the cellular and molecular events underlying this process in both invertebrate and vertebrate organs. Thus, in this review, we focus on the common themes that have emerged from such comparative analyses and discuss how they are implemented via a battery of signaling pathways to ensure proper branching morphogenesis in diverse systems.
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Affiliation(s)
- Pengfei Lu
- Department of Anatomy and Program in Developmental Biology, School of Medicine, University of California at San Francisco, San Francisco, CA 94143-0452, USA
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77
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Abstract
Unlike other branched organs, the mammary gland undergoes most of its branching during adolescent rather than embryonic development. Its morphogenesis begins in utero, pauses between birth and puberty, and resumes in response to ovarian estrogens to form an open ductal tree that eventually fills the entire mammary fat pad of the young female adult. Importantly, this "open" architecture leaves room during pregnancy for the organ to develop milk-producing alveoli like leaves on otherwise bare branches. Thereafter, the ducts serve to deliver the milk that is produced throughout lactation. The hormonal cues that elicit these various phases of mammary development utilize local signaling cascades and reciprocal stromal-epithelial interactions to orchestrate the tissue reorganization, differentiation and specific activities that define each phase. Fortunately, the mammary gland is rather amenable to experimental inquiry and, as a result, we have a fair, although incomplete, understanding of the mechanisms that control its development. This review discusses our current sense and understanding of those mechanisms as they pertain to mammary branching, with the caveat that many more aspects are still waiting to be solved.
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Affiliation(s)
- Mark D Sternlicht
- Department of Anatomy and Program in Biomedical Sciences, University of California, San Francisco, CA 94143-0452, USA.
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78
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Jung AC, Ribeiro C, Michaut L, Certa U, Affolter M. Polychaetoid/ZO-1 is required for cell specification and rearrangement during Drosophila tracheal morphogenesis. Curr Biol 2006; 16:1224-31. [PMID: 16782014 DOI: 10.1016/j.cub.2006.04.048] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2006] [Revised: 04/13/2006] [Accepted: 04/24/2006] [Indexed: 11/25/2022]
Abstract
The development of the complex network of epithelial tubes that ultimately forms the Drosophila tracheal system relies on cell migration, cell shape changes, cell rearrangements, cell differentiation, and branch fusion . Most of these events are controlled by a combination of distinct transcription factors and cell-cell signaling molecules, but few proteins that do not fall within these two functional classes have been associated with tracheal development. We show that the MAGUK protein Polychaetoid (Pyd/ZO-1), the Drosophila homolog of the junctional protein ZO-1 , plays a dual role in the formation of tracheal tubes. pyd/ZO-1 mutant embryos display branch fusion defects due to the lack of reliable determination of the fusion cell fate. In addition, pyd/ZO-1 mutant embryos show impaired cell intercalation in thin tracheal branches. Pyd/ZO-1 localizes to the adherens junctions (AJs) in tracheal cells and might thus play a direct role in the regulation of the dynamic state of the AJ during epithelial remodeling. Our study suggests that MAGUK proteins might play important roles during AJ remodeling in epithelial morphogenesis.
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Affiliation(s)
- Alain C Jung
- Abteilung Zellbiologie, Biozentrum der Universität Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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79
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Cela C, Llimargas M. Egfr is essential for maintaining epithelial integrity during tracheal remodelling in Drosophila. Development 2006; 133:3115-25. [PMID: 16831830 DOI: 10.1242/dev.02482] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A fundamental requirement during organogenesis is to preserve tissue integrity to render a mature and functional structure. Many epithelial organs, such as the branched tubular structures, undergo a tremendous process of tissue remodelling to attain their final pattern. The cohesive properties of these tissues need to be finely regulated to promote adhesion yet allow flexibility during extensive tissue remodelling. Here, we report a new role for the Egfr pathway in maintaining epithelial integrity during tracheal development in Drosophila. We show that the integrity-promoting Egfr function is transduced by the ERK-type MAPK pathway, but does not require the downstream transcription factor Pointed. Compromising Egfr signalling, by downregulating different elements of the pathway or by overexpressing the Mkp3 negative regulator, leads to loss of tube integrity, whereas upregulation of the pathway results in increased tissue stiffness. We find that regulation of MAPK pathway activity by Breathless signalling does not impinge on tissue integrity. Egfr effects on tissue integrity correlate with differences in the accumulation of markers for cadherin-based cell-cell adhesion. Accordingly, downregulation of cadherin-based cell-cell adhesion gives rise to tracheal integrity defects. Our results suggest that the Egfr pathway regulates maintenance of tissue integrity, at least in part, through the modulation of cell adhesion. This finding establishes a link between a developmental pathway governing tracheal formation and cell adhesiveness.
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Affiliation(s)
- Carolina Cela
- Institut de Biologia Molecular de Barcelona (IBMB Samitier 1-5, 08028 Barcelona, Spain
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80
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Ghabrial AS, Krasnow MA. Social interactions among epithelial cells during tracheal branching morphogenesis. Nature 2006; 441:746-9. [PMID: 16760977 DOI: 10.1038/nature04829] [Citation(s) in RCA: 179] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2005] [Accepted: 04/19/2006] [Indexed: 11/09/2022]
Abstract
Many organs are composed of tubular networks that arise by branching morphogenesis in which cells bud from an epithelium and organize into a tube. Fibroblast growth factors (FGFs) and other signalling molecules have been shown to guide branch budding and outgrowth, but it is not known how epithelial cells coordinate their movements and morphogenesis. Here we use genetic mosaic analysis in Drosophila melanogaster to show that there are two functionally distinct classes of cells in budding tracheal branches: cells at the tip that respond directly to Branchless FGF and lead branch outgrowth, and trailing cells that receive a secondary signal to follow the lead cells and form a tube. These roles are not pre-specified; rather, there is competition between cells such that those with the highest FGF receptor activity take the lead positions, whereas those with less FGF receptor activity assume subsidiary positions and form the branch stalk. Competition appears to involve Notch-mediated lateral inhibition that prevents extra cells from assuming the lead. There may also be cooperation between budding cells, because in a mosaic epithelium, cells that cannot respond to the chemoattractant, or respond only poorly, allow other cells in the epithelium to move ahead of them.
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Affiliation(s)
- Amin S Ghabrial
- Howard Hughes Medical Institute, Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305-5307, USA
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