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[
WormBook,
2006]
A distinctive feature of polarized epithelial cells is their specialized junctions, which contribute to cell integrity and provide platforms to orchestrate cell shape changes. The chapter discusses the composition and assembly of C. elegans cell-cell and cell-extracellular matrix junctions, proteins that anchor the cytoskeleton and mechanisms involved in establishing epithelial polarity. The focus remains cellular and does not properly deal with epithelial cells in the context of the developing embryo.
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WormBook,
2014]
A distinctive feature of polarized epithelial cells is their specialized junctions, which contribute to cell integrity and provide platforms to orchestrate cell shape changes. This chapter discusses the composition, assembly and remodeling of C. elegans cell-cell (CeAJ) and hemidesmosome-like cell-extracellular matrix junctions (CeHD), proteins that anchor the cytoskeleton, and mechanisms involved in establishing epithelial polarity. Major recent progress in this area has come from the analysis of mechanisms that maintain cell polarity, which involve lipids and trafficking, and on the impact of mechanical forces on junction remodeling. This chapter focuses on cellular, rather than developmental, aspects of epithelial cells.
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[
Cell,
1998]
Muscle contraction is controlled by motor neurons, which are activated by glutamate release in spinal cord. This stimulus triggers action potentials that are propagated down long motor neuron axons to mediate acetylcholine release at distant neuromuscular junctions. This vectorial signaling in a motor neuron requires polarized sorting of proteins to appropriate neuronal domains. Neurotransmitter receptors for glutamate must be targeted to dendrites, while proteins that mediate synthesis and release of acetylcholine are shuttled down axons. Many nonneuronal cells are also polarized, but the two polarized faces are typically much closer than in neurons. For example, intestinal epithelial cells have an apical surface that faces the lumen of the gut and a basolateral surface that contacts the underlying basement membrane. Uptake of nutrients by epithelial cells requires that transporters for glucose and amino acids are expressed selectively at the apical membrane and that Na+/K+ ATPases, which set up ionic gradients essential for resorption, are expressed at the basolateral membrane. Understanding the basis for cellular polarity is important as defects in protein sorting underlie several common human disorders including cystic fibrosis and polycystic kidney disease.
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BMC Biol,
2012]
The dramatic ingression of tissue sheets that accompanies many morphogenetic processes, most notably gastrulation, has been largely attributed to contractile circum-apical actomyosin 'purse-strings' in the infolding cells. Recent studies, however, including one in BMC Biology, expose mechanisms that rely less on actomyosin contractility of purse-string bundles and more on dynamics in the global cortical actomyosin network of the cells. These studies illustrate how punctuated actomyosin contractions and flow of these networks can remodel both epithelial and planarly organized mesenchymal sheets.
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[
Gene,
2001]
Epithelial cells are essential and abundant in all multicellular animals where their dynamic cell shape changes orchestrate morphogenesis of the embryo and individual organs. Genetic analysis in the simple nematode Caenorhabditis elegans provides some clues to the mechanisms isms that are involved in specifying epithelial cell fates and in controlling specific epithelial processes such as junction assembly, trafficking or cell fusion and cell adhesion. Here we review recent findings concerning C elegans epithelial cells, focusing in particular on epithelial polarity, and transcriptional control.
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[
Science,
2002]
The polarized nature of epithelial cells is manifested by the nonrandom partitioning of organelles within the cells, the concentration of intercellular junctions at one pole, and the asymmetric distribution of proteins and lipids within the plasma membrane. These features allow epithelia to fulfill their specific tasks, such as targeted uptake and secretion of molecules and the segregation of different tissue compartments. The accessibility of Drosophila melanogaster and Caenorhabditis elegans to genetic and cell biological analyses, combined with the study of mammalian cells in culture, provides an ideal basis for understanding the mechanisms that control the establishment and maintenance of epithelial cell polarity and tissue integrity. Here, we focus on some of the best-studied junctions and membrane-associated protein complexes and their relation to cell polarity. Comparisons between fly, worm, and vertebrate epithelia reveal marked similarities with respect to the molecules used, and pronounced differences in the organization of the junctions
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[
Exp Cell Res,
2007]
Intermediate filaments have long been considered mechanical components of the cell that provide resistance to deformation stress. Practical experimental problems, including insolubility, lack of good pharmacological antagonists, and the paucity of powerful genetic models have handicapped the research of other functions. In single-layered epithelial cells, keratin intermediate filaments are cortical, either apically polarized or apico-lateral. This review analyzes phenotypes of genetic manipulations of simple epithelial cell keratins in mice and Caenorhabditis elegans that strongly suggest a role of keratins in apico-basal polarization and membrane traffic. Published evidence that intermediate filaments can act as scaffolds for proteins involved in membrane traffic and signaling is also discussed. Such a scaffolding function would generate a highly polarized compartment within the cytoplasm of simple epithelial cells. While in most cases mechanistic explanations for the keratin-null or overexpression phenotypes are still missing, it is hoped that investigators will be encouraged to study these as yet poorly understood functions of intermediate filaments.
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[
Cells,
2016]
Intermediate filaments are abundant cytoskeletal components of epithelial tissues. They have been implicated in overall stress protection. A hitherto poorly investigated area of research is the function of intermediate filaments as a barrier to microbial infection. This review summarizes the accumulating knowledge about this interaction. It first emphasizes the unique spatial organization of the keratin intermediate filament cytoskeleton in different epithelial tissues to protect the organism against microbial insults. We then present examples of direct interaction between viral, bacterial, and parasitic proteins and the intermediate filament system and describe how this affects the microbe-host interaction by modulating the epithelial cytoskeleton, the progression of infection, and host response. These observations not only provide novel insights into the dynamics and function of intermediate filaments but also indicate future avenues to combat microbial infection.
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[
Cell Cycle,
2007]
Cells must coordinate diverse processes including cell division, cell migration, and cell polarity with the cell''s metabolic status. How single molecules coordinate these seemingly distinct cell biological events remains relatively unexplored. AMP-activated protein kinase (AMPK) sits at a unique position as a proposed energy sensor that can interface with diverse signaling molecules ranging from LKB1 to mammalian target of rapamycin (mTOR), affecting processes from ribosomal biogenesis to actin regulation. Determining biologically relevant direct kinase targets remains challenging. Alternatively, one can genetically inactivate a kinase and subsequently characterize cellular and whole animal phenotypes without the kinase''s activity. Recent genetic studies inactivating AMPK activity in Drosophila indicate unanticipated roles for AMPK as a regulator of epithelial polarity, consistent with known roles of an upstream activator, LKB1 as a PAR (partioning defective) mutant in Caenorhabditis elegans and polarity regulator. Additional genetic analyses demonstrate that both AMPK and LKB1 function are required for faithful chromosomal segregation during mitosis. At least some of these apparently divergent phenotypes may be mediated through myosin regulatory light chain, and presumably the acto-myosin complex, which can affect both polarity and cell division. Chromosomal integrity defects could also be consistent with LKB1''s role as a known human tumor suppressor gene. Elucidating the molecular players that interface with AMPK and their potential energy dependent regulation remains an important challenge to fully understand AMPK signaling.
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[
Organogenesis,
2012]
The extracellular matrix (ECM) plays an essential role in organizing tissues, defining their shapes or in presenting growth factors. Their components have been well described in most species, but our understanding of the mechanisms that control ECM remodeling remains limited. Likewise, how the ECM contributes to cellular mechanical responses has been examined in few cases. Here, I review how studies performed in C. elegans have brought several significant advances on those topics. Focusing only on epithelial cells, I discuss basement membrane invasion by the anchor cell during vulva morphogenesis, a process that has greatly expanded our knowledge of ECM remodeling in vivo. I then discuss the ECM role in a novel mechanotransduction process, whereby muscle contractions stimulate the remodeling of hemidesmosome-like junctions in the epidermis, which highlights that these junctions are mechanosensitive. Finally, I discuss progress in defining the composition and potential roles of the apical ECM covering epidermal cells in embryos.