Editorial Guide

Focus Issue: Polarity Signals--from Cell to Organism

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Science's STKE  10 Dec 2002:
Vol. 2002, Issue 162, pp. eg12
DOI: 10.1126/stke.2002.162.eg12

Polarity is a broad theme, encompassing numerous biological processes. This week, Science presents a special issue that highlights this phenomenon, from single cells to whole organisms. Indeed, establishing and maintaining left and right, front and back, and top and bottom is essential not only in single-celled organisms, but at every level of cell, tissue, and organism organization. In the absence of the polarity inherent to various biological organizations and processes, life cannot proceed normally. We are now beginning to understand how polarity is generated and maintained at a detailed molecular level. This week, STKE's Focus Issue provides additional examples of how we are unlocking some of the signaling mysteries that underlie polarity.

In their Science Review, Shapiro et al. describe how the organization of structural and regulatory proteins at bacterial poles is necessary to carry out specialized functions, such as flagella-driven motility, host cell invasion, and chemotaxis. In Perspectives from the STKE Archive, Stock et al. and Dahlquist further describe how such polarized organization facilitates the flow of signals and leads to signal amplification through the two-component machinery of the bacterial chemosensory system. Descriptions of similar two-component systems in plants and yeast can also be found in the STKE Reviews Archive (see Santos and Shiozaki; Alonso and Ecker; and Urao et al.).

Three reviews in Science describe polarity regulatory mechanisms that appear to be generally conserved in different cell types and across species. For example, factors that regulate polarity in a single cell, the egg, may also govern epithelial and neuronal cell polarity. Pellettieri and Seydoux describe how anterior-posterior asymmetry first arises in the egg through par genes in flies and worms. An STKE Perspective from the Archive by Stein and Stevens describes how the receptor tyrosine kinase Torso and a putative ligand called Trunk also define the anterior and posterior ends of the Drosophila embryo. During development, asymmetric cell divisions, in which precursor cells give rise to entirely different sibling cells, also contribute to the future body plan. The STKE Perspective by Shen and Temple describes how asymmetric distribution of intracellular signaling components may contribute to the phenotypic differences between two sister cells. Numb is an adaptor protein that binds to and inhibits the cell surface receptor Notch, and the skewed distribution of Numb prior to cell division has been observed in the Drosophila sensory organ precursor cell. The authors also discuss how Numb may link the endocytic machinery with cell fate determination (see also the STKE Perspective from the Archive by Krämer on Notch and endocytosis). The STKE Perspective by Gonzalez continues this theme, discussing research implicating a member of the mitotic serine-threonine Aurora kinase family in regulation of the polarized localization of Numb.

During development, cells undergo polarized morphogenic movements that drive organized pattern formation and elaborate the body axes. The Science review by Keller describes how many of the genes that control cellular protrusions, cell intercalation, and convergent-extension cell movements during development have counterparts that control epithelial cell polarity. Parallel pathways include the planar cell polarity signaling pathway that involves the secreted protein Wnt and its cognate receptor Frizzled (as opposed to the canonical Wnt-β-catenin pathway, which is described in the STKE Connections Maps). This pathway may impinge on the Rho family of small guanosine triphosphatases (GTPases), thus regulating the cytoskeleton. An STKE Perspective from the Archive by Palazzo and Gundersen describes how the actin and microtubule cytoskeltons coordinately generate polarized cell migration.

The Science review by Knust and Bossinger provides a detailed account of junctional protein complexes in epithelial cells across species, revealing similarities and difference in their composition and organization. The junctions not only maintain the polar integrity of these cells structurally, but, because they harbor specific signaling complexes, the cells rely on these junctions to fulfill specialized tasks.

In the Archive, an STKE Perspective by Manseau explains how, like proteins and lipids, RNA can be localized apically or basolaterally to ensure appropriate availability of the encoded product at the right time.

Cells can move in specific directions according to the extracellular cues that they sense. The neuron is a cell with exquisite polarity, whose growth cone, at the end of a single extending axon, is confronted by a wealth of attractive and repulsive cues. The Science review by Dickson describes how molecules including netrins, slits, semaphorins, and ephrins, provide an elaborate guidance system during neuronal development. See the related STKE articles on netrins (Merz and Culotti), semaphorins (He et al. and Ventura and Pelicci), and ephrins (by Boyd and Lackmann).

Polarized growth also occurs in plants during development and during reproduction. The STKE Perspective by Robinson and Messerli describes how oscillating concentration of cytosolic ions initiate signaling processes that control mobilization of membranes, cytoskeleton, and cytosolic components to direct the polarized growth of angiosperm pollen tubes.

Understanding the genetic and molecular basis of polarized cell organization and behavior remains an exciting challenge, and it is clear that by exploiting different organismal and cellular systems, commonalities in signaling themes will continue to be revealed.

Featured in This Focus Issue

  • Perspective by C. Gonzalez, Aurora-A in cell fate control. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/162/pe45. [Summary] [Full Text]

  • Perspective by K. R. Robinson, M. A. Messerli, Pulsating ion fluxes and growth at the pollen tube tip. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/162/pe45. [Summary] [Full Text]

  • Perspective by Q. Shen, S. Temple, Creating asymmetric cell divisions by skewing endocytosis. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/162/pe52. [Summary] [Full Text]

  • Virtual Journal: B. Dickson, Molecular mechanisms of axon guidance. Science 298, 1959-1964 (2002). [Abstract] [Full Text]

  • Virtual Journal: R. Keller, Shaping the vertebrate body plan by polarized embryonic cell movements. Science 298, 1950-1954 (2002). [Abstract] [Full Text]

  • Virtual Journal: E. Knust, O. Bossinger, Composition and formation of intercellular junctions in epithelial cells. Science 298, 1955-1959 (2002). [Abstract] [Full Text]

  • Virtual Journal: J. Pellettieri, G. Seydoux, Anterior/posterior polarity in C. elegans and Drosophila - PARallels and differences. Science 298, 1946-1950 (2002). [Abstract] [Full Text]

  • Virtual Journal: L. Shapiro, H. H. McAdams, Richard Losick, Generating and exploiting polarity in bacteria. Science 298, 1942-1946 (2002). [Abstract] [Full Text]

Related Resources as STKE

  • Connections Map by R. Moon, Wnt/β-catenin pathway. Science's STKE (Connections Map as seen October 2002), http://stke.sciencemag.org/cgi/cm/CMP_5533. [Canonical Pathway]

  • Connections Map by M. Boutros, N. Perrimon, Drosophila Wnt/Fz pathway. Science's STKE (Connections Map as seen October 2002), http://stke.sciencemag.org/cgi/cm/CMP_6459. [Specific Pathway]

  • Review by J. M. Alonso, J. R. Ecker, The ethylene pathway: A paradigm for plant hormone signaling and interaction. Science's STKE (2001), http://stke.sciencemag.org/cgi/content/full/sigtrans;2001/70/re1. [Gloss] [Abstract] [Full Text]

  • Review by A. W. Boyd, M. Lackmann, Signals from Eph and Ephrin proteins: A developmental tool kit. Science's STKE (2001), http://stke.sciencemag.org/cgi/content/full/sigtrans;2001/112/re20. [Gloss] [Abstract] [Full Text] [Movie 1] [Movie 2]

  • Review by Z. He, K. C. Wang, V. Koprivica, G. Ming, H.-J. Song, Knowing how to navigate: Mechanisms of semaphorin signaling in the nervous system. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/119/re1. [Gloss] [Abstract] [Full Text]

  • Review by J. L. Santos, K. Shiozaki, Fungal histidine kinases. Science's STKE (2001), http://stke.sciencemag.org/cgi/content/full/sigtrans;2001/98/re1. [Gloss] [Abstract] [Full Text]

  • Review by T. Urao, K. Yamaguchi-Shinozaki, K. Shinozaki, Plant histidine kinases: An emerging picture of two-component signal transduction in hormone and environmental responses. Science's STKE (2001), http://stke.sciencemag.org/cgi/content/full/sigtrans;2001/109/re18. [Gloss] [Abstract] [Full Text]

  • Perspective by F. W. Dahlquist, Amplification of signaling events in bacteria. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/132/pe24. [Summary] [Full Text]

  • Perspective by P. A. Iglesias, A. Levchenko, Modeling the cell's guidance system. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/148/pe12. [Summary] [Full Text]

  • Perspective by H. Krämer, RIPping Notch apart: A new role for endocytosis in signal transduction? Science's STKE (2000), http://stke.sciencemag.org/cgi/content/full/sigtrans;2000/29/pe1. [Summary] [Full Text] [Movie 1]

  • Perspective by K. S. Kosik, A. M. Krichevsky, The message and the messenger: Delivering RNA in neurons. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/126/pe16. [Summary] [Full Text]

  • Perspective by L. J. Manseau, RNA localization meets Wingless signaling. Science's STKE (2001), http://stke.sciencemag.org/cgi/content/full/sigtrans;2001/92/pe1. [Summary] [Full Text]

  • Perspective by A. Martinez Arias, The informational content of gradients of Wnt proteins. Science's STKE (2000), http://stke.sciencemag.org/cgi/content/full/sigtrans;2000/43/pe1. [Summary] [Full Text]

  • Perspective by D. C. Merz, J. G. Culotti, Getting directions: Axon guidance receptors find the way. Science's STKE (1999), http://stke.sciencemag.org/cgi/content/full/sigtrans;1999/5/pe1. [Summary] [Full Text]

  • Perspective by A. F. Palazzo, G. G. Gundersen, Microtubule-actin cross-talk at focal adhesions. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/139/pe31. [Summary] [Full Text]

  • Perspective by D. Stein, L. M. Stevens, The Torso ligand, unmasked? Science's STKE (2001), http://stke.sciencemag.org/cgi/content/full/sigtrans;2001/98/pe2. [Summary] [Full Text]

  • Perspective by J. B. Stock, M. N. Levit, P. M. Wolanin, Information processing in bacterial chemotaxis. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/132/pe25. [Summary] [Full Text]

  • Perspective by M. van den Heuvel, Fat hedgehogs, slower or richer? Science's STKE (2001), http://stke.sciencemag.org/cgi/content/full/sigtrans;2001/100/pe31. [Summary] [Full Text]

  • Perspective by A. Ventura, P. G. Pelicci, Semaphorins: Green light for redox signaling. Science's STKE (2002), http://stke.sciencemag.org/cgi/content/full/sigtrans;2002/155/pe44. [Summary] [Full Text]

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