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Avila A, Zhang SL. A circadian clock regulates the blood-brain barrier across phylogeny. VITAMINS AND HORMONES 2024; 126:241-287. [PMID: 39029975 DOI: 10.1016/bs.vh.2024.04.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/21/2024]
Abstract
As the central regulatory system of an organism, the brain is responsible for overseeing a wide variety of physiological processes essential for an organism's survival. To maintain the environment necessary for neurons to function, the brain requires highly selective uptake and elimination of specific molecules through the blood-brain barrier (BBB). As an organism's activities vary throughout the day, how does the BBB adapt to meet the changing needs of the brain? A mechanism is through temporal regulation of BBB permeability via its circadian clock, which will be the focal point of this chapter. To comprehend the circadian clock's role within the BBB, we will first examine the anatomy of the BBB and the transport mechanisms enabling it to fulfill its role as a restrictive barrier. Next, we will define the circadian clock, and the discussion will encompass an introduction to circadian rhythms, the Transcription-Translation Feedback Loop (TTFL) as the mechanistic basis of circadian timekeeping, and the organization of tissue clocks found in organisms. Then, we will cover the role of the circadian rhythms in regulating the cellular mechanisms and functions of the BBB. We discuss the implications of this regulation in influencing sleep behavior, the progression of neurodegenerative diseases, and finally drug delivery for treatment of neurological diseases.
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Affiliation(s)
- Ashley Avila
- Cell Biology Department, Emory University, Atlanta, GA, United States
| | - Shirley L Zhang
- Cell Biology Department, Emory University, Atlanta, GA, United States.
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2
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De O, Rice C, Zulueta-Coarasa T, Fernandez-Gonzalez R, Ward RE. Septate junction proteins are required for cell shape changes, actomyosin reorganization and cell adhesion during dorsal closure in Drosophila. Front Cell Dev Biol 2022; 10:947444. [PMID: 36238688 PMCID: PMC9553006 DOI: 10.3389/fcell.2022.947444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Accepted: 08/29/2022] [Indexed: 11/13/2022] Open
Abstract
Septate junctions (SJs) serve as occluding barriers in invertebrate epithelia. In Drosophila, at least 30 genes are required for the formation or maintenance of SJs. Interestingly, loss-of-function mutations in core SJ components are embryonic lethal, with defects in developmental events such as head involution and dorsal closure (DC) that occur prior to the formation of a mature SJ, indicating a role for these proteins in mid-embryogenesis independent of their occluding function. To understand this novel function in development, we examined loss-of-function mutations in three core SJ proteins during the process of DC. DC occurs during mid-embryogenesis to seal a dorsal gap in the epidermis following germ band retraction. Closure is driven by contraction of the extraembryonic amnioserosa cells that temporarily cover the dorsal surface and by cell shape changes (elongation) of lateral epidermal cells that bring the contralateral sheets together at the dorsal midline. Using live imaging and examination of fixed tissues, we show that early events in DC occur normally in SJ mutant embryos, but during later closure, coracle, Macroglobulin complement-related and Neurexin-IV mutant embryos exhibit slower rates of closure and display aberrant cells shapes in the dorsolateral epidermis, including dorsoventral length and apical surface area. SJ mutant embryos also show mild defects in actomyosin structures along the leading edge, but laser cutting experiments suggest similar tension and viscoelastic properties in SJ mutant versus wild type epidermis. In a high percentage of SJ mutant embryos, the epidermis tears free from the amnioserosa near the end of DC and live imaging and immunostaining reveal reduced levels of E-cadherin, suggesting that defective adhesion may be responsible for these tears. Supporting this notion, reducing E-cadherin by half significantly enhances the penetrance of DC defects in coracle mutant embryos.
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Affiliation(s)
- Oindrila De
- Department of Biology, Case Western Reserve University, Cleveland, Ohio, United States
| | - Clinton Rice
- Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, United States
| | | | | | - Robert E Ward
- Department of Biology, Case Western Reserve University, Cleveland, Ohio, United States
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Rice C, De O, Alhadyian H, Hall S, Ward RE. Expanding the Junction: New Insights into Non-Occluding Roles for Septate Junction Proteins during Development. J Dev Biol 2021; 9:11. [PMID: 33801162 PMCID: PMC8006247 DOI: 10.3390/jdb9010011] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 03/15/2021] [Accepted: 03/17/2021] [Indexed: 12/17/2022] Open
Abstract
The septate junction (SJ) provides an occluding function for epithelial tissues in invertebrate organisms. This ability to seal the paracellular route between cells allows internal tissues to create unique compartments for organ function and endows the epidermis with a barrier function to restrict the passage of pathogens. Over the past twenty-five years, numerous investigators have identified more than 30 proteins that are required for the formation or maintenance of the SJs in Drosophila melanogaster, and have determined many of the steps involved in the biogenesis of the junction. Along the way, it has become clear that SJ proteins are also required for a number of developmental events that occur throughout the life of the organism. Many of these developmental events occur prior to the formation of the occluding junction, suggesting that SJ proteins possess non-occluding functions. In this review, we will describe the composition of SJs, taking note of which proteins are core components of the junction versus resident or accessory proteins, and the steps involved in the biogenesis of the junction. We will then elaborate on the functions that core SJ proteins likely play outside of their role in forming the occluding junction and describe studies that provide some cell biological perspectives that are beginning to provide mechanistic understanding of how these proteins function in developmental contexts.
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Affiliation(s)
- Clinton Rice
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA; (C.R.); (H.A.)
| | - Oindrila De
- Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA;
| | - Haifa Alhadyian
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA; (C.R.); (H.A.)
| | | | - Robert E. Ward
- Department of Biology, Case Western Reserve University, Cleveland, OH 44106, USA;
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Griffith MB. Toxicological perspective on the osmoregulation and ionoregulation physiology of major ions by freshwater animals: Teleost fish, crustacea, aquatic insects, and Mollusca. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2017; 36:576-600. [PMID: 27808448 PMCID: PMC6114146 DOI: 10.1002/etc.3676] [Citation(s) in RCA: 91] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Revised: 04/11/2016] [Accepted: 11/01/2016] [Indexed: 05/21/2023]
Abstract
Anthropogenic sources increase freshwater salinity and produce differences in constituent ions compared with natural waters. Moreover, ions differ in physiological roles and concentrations in intracellular and extracellular fluids. Four freshwater taxa groups are compared, to investigate similarities and differences in ion transport processes and what ion transport mechanisms suggest about the toxicity of these or other ions in freshwater. Although differences exist, many ion transporters are functionally similar and may belong to evolutionarily conserved protein families. For example, the Na+ /H+ -exchanger in teleost fish differs from the H+ /2Na+ (or Ca2+ )-exchanger in crustaceans. In osmoregulation, Na+ and Cl- predominate. Stenohaline freshwater animals hyperregulate until they are no longer able to maintain hypertonic extracellular Na+ and Cl- concentrations with increasing salinity and become isotonic. Toxic effects of K+ are related to ionoregulation and volume regulation. The ionic balance between intracellular and extracellular fluids is maintained by Na+ /K+ -adenosine triphosphatase (ATPase), but details are lacking on apical K+ transporters. Elevated H+ affects the maintenance of internal Na+ by Na+ /H+ exchange; elevated HCO3- inhibits Cl- uptake. The uptake of Mg2+ occurs by the gills or intestine, but details are lacking on Mg2+ transporters. In unionid gills, SO42- is actively transported, but most epithelia are generally impermeant to SO42- . Transporters of Ca2+ maintain homeostasis of dissolved Ca2+ . More integration of physiology with toxicology is needed to fully understand freshwater ion effects. Environ Toxicol Chem 2017;36:576-600. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.
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Affiliation(s)
- Michael B. Griffith
- Office of Research and Development, National Center for Environmental Assessment, US Environmental Protection Agency, Cincinnati, Ohio, USA
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5
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Septate Junction Proteins Play Essential Roles in Morphogenesis Throughout Embryonic Development in Drosophila. G3-GENES GENOMES GENETICS 2016; 6:2375-84. [PMID: 27261004 PMCID: PMC4978892 DOI: 10.1534/g3.116.031427] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The septate junction (SJ) is the occluding junction found in the ectodermal epithelia of invertebrate organisms, and is essential to maintain chemically distinct compartments in epithelial organs, to provide the blood–brain barrier in the nervous system, and to provide an important line of defense against invading pathogens. More than 20 genes have been identified to function in the establishment or maintenance of SJs in Drosophila melanogaster. Numerous studies have demonstrated the cell biological function of these proteins in establishing the occluding junction, whereas very few studies have examined further developmental roles for them. Here we examined embryos with mutations in nine different core SJ genes and found that all nine result in defects in embryonic development as early as germ band retraction, with the most penetrant defect observed in head involution. SJ genes are also required for cell shape changes and cell rearrangements that drive the elongation of the salivary gland during midembryogenesis. Interestingly, these developmental events occur at a time prior to the formation of the occluding junction, when SJ proteins localize along the lateral membrane and have not yet coalesced into the region of the SJ. Together, these observations reveal an underappreciated role for a large group of SJ genes in essential developmental events during embryogenesis, and suggest that the function of these proteins in facilitating cell shape changes and rearrangements is independent of their role in the occluding junction.
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6
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Occluding junctions of invertebrate epithelia. J Comp Physiol B 2015; 186:17-43. [DOI: 10.1007/s00360-015-0937-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Revised: 09/12/2015] [Accepted: 09/22/2015] [Indexed: 01/30/2023]
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7
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Kornakova EE. Ultrastructural and morphological features of the turbellarian worm Bothrioplana semperi and problem of monophyly of Seriata (Platyhelminthes, Turbellaria). J EVOL BIOCHEM PHYS+ 2013. [DOI: 10.1134/s0022093013020138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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8
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Abstract
The intestine consists of epithelial cells that secrete digestive enzymes and mucus (gland cells), absorb food particles (enterocytes), and produce hormones (endocrine cells). Intestinal cells are rapidly turned over and need to be replaced. In cnidarians, mitosis of differentiated intestinal cells accounts for much of the replacement; in addition, migratory, multipotent stem cells (interstitial cells) contribute to the production of intestinal cells. In other phyla, intestinal cell replacement is solely the function of stem cells entering the gut from the outside (such as in case of the neoblasts of platyhelminths) or intestinal stem cells located within the midgut epithelium (as in both vertebrates or arthropods). We will attempt in the following to review important aspects of midgut stem cells in different animal groups: where are they located, what types of lineages do they produce, and how do they develop. We will start out with a comparative survey of midgut cell types found across the animal kingdom; then briefly look at the specification of these cells during embryonic development; and finally focus on the stem cells that regenerate midgut cells during adult life. In a number of model systems, including mouse, zebrafish and Drosophila, the molecular pathways controlling intestinal stem cells proliferation and the specification of intestinal cell types are under intensive investigation. We will highlight findings of the recent literature, focusing on aspects that are shared between the different models and that point at evolutionary ancient mechanisms of intestinal cell formation.
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9
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Leiserson WM, Keshishian H. Maintenance and regulation of extracellular volume and the ion environment in Drosophila larval nerves. Glia 2011; 59:1312-21. [PMID: 21305613 DOI: 10.1002/glia.21132] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Accepted: 12/01/2010] [Indexed: 11/07/2022]
Abstract
In mammals and insects, paracellular blood barriers isolate the nervous system from the rest of the animal. Glia and accessory cells of the nervous system use pumps, channels, cotransporters, and exchangers collectively to maintain the extracellular ion environment and osmotic balance in the nervous system. At present, the molecular mechanisms that regulate this process remain unclear. In humans, loss of extracellular ion and volume regulation in the nervous system poses serious health threats. Drosophila is a model genetic organism with a proven track record for uncovering molecular mechanisms relevant to human health and disease. Here, we review what is known about extracellular ion and volume regulation in larval abdominal nerves, present some new data about the impact of neural activity on the extracellular environment, and relate the findings to mammalian systems. Homologies have been found at the level of morphology, physiology, molecular mechanisms, and mutant phenotypes. The Fray-Ncc69 module regulates extracellular volume in larval nerves. Genetic rescue experiments with the mammalian orthologs prove this module has a direct correlate in humans. This and other molecular homologies, together with the similar physiological needs, suggest that uncovering the molecular mechanisms of ion and volume regulation in larval nerves will likely provide significant insights into this process in mammalian systems.
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Affiliation(s)
- William M Leiserson
- Molecular, Cellular, and Developmental Biology Department, Yale University, P.O. Box 208103, New Haven, Connecticut 06520-8103, USA.
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10
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Morris J, Ladurner P, Rieger R, Pfister D, Del Mar De Miguel-Bonet M, Jacobs D, Hartenstein V. The Macrostomum lignano EST database as a molecular resource for studying platyhelminth development and phylogeny. Dev Genes Evol 2006; 216:695-707. [PMID: 17021863 DOI: 10.1007/s00427-006-0098-z] [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] [Received: 03/31/2006] [Accepted: 06/20/2006] [Indexed: 12/31/2022]
Abstract
We report the development of an Expressed Sequence Tag (EST) resource for the flatworm Macrostomum lignano. This taxon is of interest due to its basal placement within the flatworms. As such, it provides a useful comparative model for understanding the development of neural and sensory organization. It was anticipated on the basis of previous studies [e.g., Sánchez-Alvarado et al., Development, 129:5659-5665, (2002)] that a wide range of developmental markers would be expressed in later-stage macrostomids, and this proved to be the case, permitting recovery of a range of gene sequences important in development. To this end, an adult Macrostomum cDNA library was generated and 7,680 Macrostomum ESTs were sequenced from the 5' end. In addition, 1,536 of these aforementioned sequences were sequenced from the 3' end. Of the roughly 5,416 non-redundant sequences identified, 68% are similar to previously reported genes of known function. In addition, nearly 100 specific clones were obtained with potential neural and sensory function. From these data, an annotated searchable database of the Macrostomum EST collection has been made available on the web. A major objective was to obtain genes that would allow reconstruction of embryogenesis, and in particular neurogenesis, in a basal platyhelminth. The sequences recovered will serve as probes with which the origin and morphogenesis of lineages and tissues can be followed. To this end, we demonstrate a protocol for combined immunohistochemistry and in situ hybridization labeling in juvenile Macrostomum, employing homologs of lin11/lim1 and six3/optix. Expression of these genes is shown in the context of the neuropile/muscle system.
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Affiliation(s)
- Joshua Morris
- Department of Molecular, Cell and Developmental Biology, University of California Los Angeles, Los Angeles, CA 90095, USA
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12
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Carlson SD, Juang JL, Hilgers SL, Garment MB. Blood barriers of the insect. ANNUAL REVIEW OF ENTOMOLOGY 2000; 45:151-174. [PMID: 10761574 DOI: 10.1146/annurev.ento.45.1.151] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The blood-brain barrier (BBB) ensures brain function in vertebrates and insects by maintaining ionic integrity of the neuronal bathing fluid. Without this barrier, paralysis and death ensue. The structural analogs of the BBB are occlusive (pleated-sheet) septate and tight junctions between perineurial cells, glia and perineurial cells, and possibly between glia. Immature Diptera have such septate junctions (without tight junctions) while both junctional types are found in the imago. Genetic and molecular biology of these junctions are discussed, namely tight (occludin) and pleated-sheet septate (neurexin IV). A temporal succession of blood barriers form in immature Diptera. The first barrier forms in the peripheral nervous system where pleated-sheet septate junctions bond cells of the nascent (embryonic) chordotonal organs in early neurogenesis. At the end of embryonic life, the central nervous system is fully vested with a blood-brain barrier. A blood-eye barrier arises in early pupal life. Future prospects in blood-barrier research are discussed.
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Affiliation(s)
- S D Carlson
- Department of Entomology, University of Wisconsin-Madison 53706, USA.
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Dietz TH, Wilcox SJ, Silverman H, Byrne RA. Effects of hyperosmotic challenge on the freshwater bivalveDreissena polymorpha: importance of K+. CAN J ZOOL 1997. [DOI: 10.1139/z97-090] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The effects of elevated ion concentrations in the bathing medium on ionoregulation and mortality rate were examined in the freshwater bivalve Dreissena polymorpha. The survival of mussels in saline water depended on the balance of Na+and K+in the medium. Animals acclimated to artificial pond water tolerated acute transfer to 108 mosmol artificial seawater (3.5‰) for months with virtually no mortality. Dreissena polymorpha rapidly (~ 12 h) became isosmotic to the bathing medium when exposed to approximately 100 mosmol hyperosmotic solution composed of 45 mM NaCl or 3.5‰ artificial seawater. This was primarily due to a rapid accumulation of ions with some osmotic loss of water. During a hyperosmotic challenge the intracellular compartment gained K+but mussels required exogenous K+to maintain an intracellular to extracellular gradient similar to that of control animals. The epithelia of D. polymorpha were remarkably "leaky" to solutes. Under hyperosmotic conditions, sucrose, glucose, and inulin penetrated the epithelial tissue and appeared in the blood. The principal route of solute entry was likely paracellular pathways. However, the estimated net movement of sucrose or glucose was less than 2% of the net flux of NaCl. Dreissena polymorpha have the capacity to tolerate oligohaline water where sufficient K+is available to promote cellular homeostasis.
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14
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McGee C, Fairweather I, Blackshaw RP. Ultrastructural observations on rhabdite formation in the planarian,Artioposthia triangulata. J Zool (1987) 1996. [DOI: 10.1111/j.1469-7998.1996.tb05306.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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15
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Dan-Sohkawa M, Kaneko H, Noda K. Paracellular, transepithelial permeation of macromolecules in the body wall epithelium of starfish embryos. ACTA ACUST UNITED AC 1995. [DOI: 10.1002/jez.1402710404] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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16
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Shires R, Lane N, Inman C, Lockwood A. Microtubule systems associated with the septate junctions of the gill cells of four gammarid amphipods. Tissue Cell 1995; 27:3-12. [DOI: 10.1016/s0040-8166(95)80003-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/1994] [Accepted: 08/29/1994] [Indexed: 10/25/2022]
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17
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Shires R, Lane N, Inman C, Lockwood A. Structural changes in the gill cells of Gammarus duebeni (Crustacea, amphipoda) under osmotic stress; with notes on microtubules in association with the septate junctions. Tissue Cell 1994; 26:767-78. [DOI: 10.1016/0040-8166(94)90059-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/1994] [Accepted: 06/01/1994] [Indexed: 11/26/2022]
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18
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Prior DJ, Maugel TK, Sellers M. Morphological correlate of regional partitioning of integumental water absorption in terrestrial slugs. Tissue Cell 1994; 26:421-9. [PMID: 8073419 DOI: 10.1016/0040-8166(94)90025-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
An ultrastructural study of the foot surface of the terrestrial mollusc, Limax maximus, has revealed a correlation of epithelial cell type with the functional partitioning of the surface. The lateral absorptive bands of the foot are comprised exclusively of microvillar epithelial cells, while those of the medial locomotor band are all ciliated. Thus, there is a clear partitioning of epithelial cell types between areas of the foot surface with distinct functional roles. Consistent with the proposed role for paracellular absorption, varying states of hydration are shown to affect the extent of the intercellular spaces, but not the intracellular architecture.
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Affiliation(s)
- D J Prior
- Department of Biological Sciences, Northern Arizona University, Flagstaff 86011
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19
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Pannabecker TL, Hayes TK, Beyenbach KW. Regulation of epithelial shunt conductance by the peptide leucokinin. J Membr Biol 1993; 132:63-76. [PMID: 8459448 DOI: 10.1007/bf00233052] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti spontaneously secrete NaCl, KCl and water across an epithelium of modest transepithelial resistance (40-80 omega cm2) and high transepithelial voltage (30-70 mV, lumen positive). Transepithelial electrochemical potentials indicate that Na and K are secreted by active and Cl by passive transport mechanisms. The addition of synthetic leucokinin-VIII (LK-VIII, insect myotropic peptide) to the peritubular bath significantly increases the rates of transepithelial NaCl, KCl and water secretion. In parallel, LK-VIII depolarizes the transepithelial voltage from 59.3 to 5.7 mV, decreases the transepithelial resistance from 57.7 to 9.9 omega cm2, and renders the basolateral and apical membrane voltages nearly equipotential (approximately -90 mV). Unilateral step changes of the [Cl] in the peritubular bath or tubule lumen elicit small transepithelial Cl diffusion potentials in the absence of LK-VIII but large transepithelial Cl diffusion potentials, up to 85% of Nernst equilibrium potentials, in the presence of LK-VIII. In Malpighian tubules treated with dinitrophenol for estimates of the shunt resistance Rsh, LK-VIII reduces Rsh from 52.5 to 5.8 omega cm2. Bilateral reductions of the Cl concentration in tubule lumen and peritubular bath fully restore Rsh to 55.8 omega cm2 in the presence of LK-VIII. LK-VIII has no effects when presented from the luminal side. These results suggest that LK-VIII increases the Cl conductance of the epithelial shunt via a receptor located at the basolateral side of the epithelium.
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Affiliation(s)
- T L Pannabecker
- Department of Physiology, Cornell University, Ithaca, New York 14853
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20
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A blood-brain barrier without tight junctions in the fly central nervous system in the early postembryonic stage. Cell Tissue Res 1992. [DOI: 10.1007/bf00381884] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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21
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Morris MA, Greenaway P. High affinity, Ca2+ specific atpase and Na+K+-ATPase in the gills of a supralittoral crab Leptograpsus variegatus. ACTA ACUST UNITED AC 1992; 102:15-8. [PMID: 1351813 DOI: 10.1016/0300-9629(92)90004-a] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
1. The gills of Leptograpsus variegatus contain a high-affinity, Ca(2+)-activated ATPase, probably located in the basolateral plasma membrane of the gill epithelia. 2. The affinity of the ATPase for Ca2+ is in the micromolar concentration range (6-35 mumol/l). 3. The specific activity of the enzyme did not change during the moult cycle. The ATPase probably does not contribute substantially to increased calcium influx from the medium during the post moult period. 4. The enzyme is believed to function as a selective extrusion mechanism involved in the maintenance of a low cytosolic Ca2+ level in the epithelial cells.
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Affiliation(s)
- M A Morris
- School of Biological Science, University of New South Wales, Kensington, Australia
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22
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23
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Abraham M. The male germ cell protective barrier along phylogenesis. INTERNATIONAL REVIEW OF CYTOLOGY 1991; 130:111-90. [PMID: 1778728 DOI: 10.1016/s0074-7696(08)61503-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- M Abraham
- Department of Zoology, Hebrew University of Jerusalem, Israel
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24
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Crouau Y. Sensory organs in a cavernicolous insect after cryofixation without cryoprotectants: A comparative ultrastructural study. Tissue Cell 1990; 22:245-58. [DOI: 10.1016/0040-8166(90)90027-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/1989] [Revised: 12/05/1989] [Indexed: 10/25/2022]
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25
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Miranda JC, Cavicchia JC. Junctional specializations in the seminiferous epithelium of an insect (Triatoma infestans): a freeze fracture and lanthanum tracer study. Tissue Cell 1988; 20:611-9. [PMID: 3070831 DOI: 10.1016/0040-8166(88)90062-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Intercellular junctions in the seminiferous epithelium of the testis of Triatoma infestans were examined by conventional electron microscopy, tannic acid fixation, electron-opaque tracers, and freeze-fracture techniques. Distinctive aspects of the intercellular junctions are described in different regions of the testis follicles. In the basal region, close to the basal lamina, smooth septate junctions intermingled with gap junctions were observed between sustentacular cells. In the parabasal regions of the seminiferous epithelium, plated septate junctions, 'molluscous and arthropod' type (according to the classification of Green, 1981), were observed. Over the above junctions, in the central regions, also located between sustentacular cell membranes, parallel rows of intramembrane particles form successive belts of widely spaced septate junctions in an atypical configuration. Invertebrate gap junctions were also observed between adjacent spermatocyte membranes.
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Affiliation(s)
- J C Miranda
- Instituto de Histología y Embriología, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, Mendoza, Argentina
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Jarial MS. Fine structure of the Malpighian tubules of chironomus larva in relation to glycogen storage and fate of hemoglobin. Tissue Cell 1988; 20:355-80. [PMID: 3232139 DOI: 10.1016/0040-8166(88)90071-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The larval Malpighian tubules of Chironomus tentans were studied using light and electron microscopy. The tubules are composed of two cell types: primary and stellate cells. Both cell types lack muscles, tracheoles, and laminate crystals in the cytoplasm and mitochondria in the microvilli. The primary cells exhibit long, wide basal membrane infoldings associated with mitochondria. They have a number of canaliculi and long, closely packed microvilli. The stellate cells possess shorter interconnecting basal infoldings and shorter, well-spaced microvilli. Both cell types are linked by septate and gap junctions. They have cytoplasmic processes and pedicels which enclose narrow slits between them and that are apposed to a basal lamella. In the 'fed' larva, the cells are stuffed with glycogen which is depleted in the 'starved' larva. Both cell types are involved in the vesicular transport of biliverdin. The presence of coated vesicles, tubular elements and various forms of lysosomes in the primary cells suggests they transport and break down functional hemoglobin. Structural modification of basal infoldings, canaliculi and microvilli is strongly correlated with increased secretory activity of the Malpighian tubules in 'fed' versus 'starved' larva.
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Affiliation(s)
- M S Jarial
- Muncie Center for Medical Education, Indiana University School of Medicine, Ball State University 47306
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27
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Hori I. Formation of the septate junction in regenerating planarian gastrodermis. J Morphol 1987; 192:205-215. [DOI: 10.1002/jmor.1051920303] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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28
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O'Donovan P, Abraham M. Somatic tissue-male germ cell barrier in three hermaphrodite invertebrates:Dugesia biblica (Platyhelminthes),Placobdella costata (Annelida), andLevantina hierosolyma (Mollusca). J Morphol 1987; 192:217-227. [DOI: 10.1002/jmor.1051920304] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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29
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Keil TA, Steinbrecht R. Diffusion barriers in silkmoth sensory epithelia: Application of lanthanum tracer to olfactory sensilla of Antheraea polyphemus and Bombyx mori. Tissue Cell 1987; 19:119-34. [DOI: 10.1016/0040-8166(87)90063-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/1986] [Revised: 10/22/1986] [Indexed: 11/28/2022]
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30
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Flower N. Sealing junctions in a number of arachnid tissues. Tissue Cell 1986; 18:899-913. [DOI: 10.1016/0040-8166(86)90046-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/1986] [Revised: 06/19/1986] [Indexed: 10/27/2022]
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31
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Miranda JC, Cavicchia JC. A permeability barrier in the testis of an insect Triatoma: A freeze-fracture and lanthanum tracer study. Tissue Cell 1986; 18:461-8. [DOI: 10.1016/0040-8166(86)90065-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/1986] [Indexed: 10/27/2022]
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32
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Uglem GL, Prior DJ, Hess SD. Paracellular water uptake and molecular sieving by the foot epithelium of terrestrial slugs. J Comp Physiol B 1985; 156:285-9. [PMID: 2424952 DOI: 10.1007/bf00695784] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A paracellular pathway in the foot epithelium of Lehmannia valentiana can be opened by dehydrating the slug. Movement of water from a wet pad through the opened pathway into the haemolymph of this terrestrial slug is rapid. The sieving properties of this paracellular pathway have been determined using the reference isotope 3HOH and various 14C-labelled solutes. Paracellular uptake of 14C-insulin (Fig. 1) and 3HOH (Fig. 2) is initial rate for at least 3 min. If the wet pad contains 1,000 cpm of 14C per ml of 3HOH, slugs absorb only about 400 cpm of 14C with each ml of 3HOH absorbed representing a sieving ratio of 0.4 for insulin. The sieving ratio of 14C-inulin does not change when the concentration is increased from 0.1 to 2.5 mmol/l. Moreover, the sieving ratio of 14C-inulin was not affected significantly by the nature of the labelling, i.e., 14C-carboxyl vs 14C-methoxy. Sieving ratios for 14C-mannitol (182 Da), 14C-polyethylene glycol (4,000 Da), and 14C-inulin (5,250 Da) were 0.92, 0.63, and 0.39, respectively (Table 1), indicating that sieving is dependent on molecular size. 14C-Dextran (70,000 Da) and blue dextran (200,000 Da) were excluded from the paracellular pathway (Fig. 4). The effective pore size of the paracellular pathway was estimated using the relationships between sieving ratio and molecular weight of 3HOH and the various solutes that can pass through the pathway. The extrapolated pore size is equivalent to that of a sieve having a molecular weight cutoff of about 10,000 Da (Fig 3).
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33
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Abstract
The functional basis of tight junction design has been examined from the point of view that this rate-limiting barrier to paracellular transport is a multicompartment system. Review of the osmotic sensitivity of these structures points to the need for this sort of analysis for meaningful correlation of structure and function under a range of conditions. A similar conclusion is drawn with respect to results from voltage-clamping protocols where reversal of spontaneous transmural potential difference elicits parallel changes in both structure and function in much the same way as does reversal of naturally occurring osmotic gradients. In each case, it becomes necessary to regard the junction as a functionally polarized structure to account for observations of its rectifying properties. Lastly, the details of experimentally-induced junction deformation are examined in light of current theories of its organization; arguments are presented in favor of the view that the primary components of intramembranous organization (as viewed with freeze-fracture techniques) are lipidic rather than proteinaceous.
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34
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Swales LS. Glial cell contacts in insects: Effects of feeding on intercellular junctions. Tissue Cell 1985; 17:841-52. [DOI: 10.1016/0040-8166(85)90040-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/1985] [Indexed: 11/28/2022]
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35
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Meurice JC, Goffinet G. Ultrastructural evidence of the ion-transporting role of the adult and larval neck organ of the marine gymnomeran Cladocera (Crustacea, Branchiopoda). Cell Tissue Res 1983; 234:351-63. [PMID: 6196121 DOI: 10.1007/bf00213773] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The neck organ of adult and immature forms of four marine gymnomeran Cladocera species (Podonidae) has been characterized morphologically by light-scanning- and electron microscopy. Although displaying some special features, a comparison with organs assuming a comparable regulating function in other organisms indicates that the neck organ of the adult Podonidae exhibits ultrastructural evidence of involvement in ion-transporting mechanisms. The extensive ventral plasma membrane infoldings closely connected with the chondriom and the peculiar organization of the cuticular site associated with the subjacent apical cell limits of the organ are among the chief structural specializations. The fact that similar structures are already present in the embryonic neck organ confirms previous indirect evidence that podonid embryos can hypo-osmoregulate as soon as the ion concentration of the brood chamber rises to that of the outside medium.
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36
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Bergmann M, Greven H, Schindelmeiser J. Observations on the blood-testis barrier in a frog and a salamander. Cell Tissue Res 1983; 232:189-200. [PMID: 6603909 DOI: 10.1007/bf00222383] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
A blood-testis barrier has been demonstrated in a frog, Rana esculenta, and in a salamander, Salamandra salamandra, using lanthanum as an electron-dense marker during fixation. The tracer penetrates the interstices between somatic follicle or Sertoli cells and germ cells in regions of the testis containing spermatogonia and spermatocytes, up to the level of punctate tight junctions. The latter can be localized between the somatic cells that line seminiferous units containing spermatids and mature spermatozoa. The barrier thus appears to be established after meiosis in both species investigated, although spermatids of different developmental stages can be found in open compartments of the testis in S. salamandra.
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37
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Saint Marie RL, Carlson SD. Glial membrane specializations and the compartmentalization of the lamina ganglionaris of the housefly compound eye. JOURNAL OF NEUROCYTOLOGY 1983; 12:243-75. [PMID: 6842276 DOI: 10.1007/bf01148464] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Membrane specializations in the lamina ganglionaris of the housefly are investigated using conventional thin-section EM, freeze-fracture replication and the diffusion of colloidal lanthanum. All glial cells in the lamina are coupled by gap junctions. Desmosomes also link all glia except the epithelial glia. Extensive glia-glial and glia-neuronal septate junctions are present in the pseudocartridge zone and nuclear layer. Septate junctions in the nuclear layer intermingle with bands of interglial and glia-neuronal tight junctions. Tight junctions are also found between satellite and epithelial glia at the border of the nuclear and plexiform layers, between adjacent epithelial glial cells in the plexiform layer, between epithelial and marginal glia at the proximal boundary of the optic neuropil, between marginal glial cells, and between marginal glia and axons. Colloidal lanthanum, introduced through an incision in the cornea, penetrates the retina but is occluded from the neuropil by septate junctions in the pseudocartridge zone. The disposition of tight and septate junctions is described in relation to the compartmentalization of the lamina. Two major compartments are delineated. The first represents the nuclear layer and contains the cell bodies of second-order visual neurons (monopolar neurons). The second compartment constitutes the plexiform layer of the lamina. Within the plexiform layer, each optic cartridge is partitioned into a separate subcompartment. Also, tracheoles and axons of long visual fibres are isolated from the optic cartridges by glial tight junctions. Morphological evidence for compartmentalization is correlated with previously established electrical properties of the insect lamina ganglionaris.
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38
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Meyran JC. Segmental variations of intercellular junctions in insect Malpighian tubules: a comparative study of two species. JOURNAL OF ULTRASTRUCTURE RESEARCH 1982; 79:31-46. [PMID: 7086942 DOI: 10.1016/s0022-5320(82)90050-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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39
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Huebner E, Injeyan H. Follicular modulation during oocyte development in an insect: formation and modification of septate and gap junctions. Dev Biol 1981; 83:101-13. [PMID: 7239004 DOI: 10.1016/s0012-1606(81)80012-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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40
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41
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42
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Abstract
Extensive and unequivocal tight junctions are here reported between the lateral borders of the cellular layer that circumscribes the arachnid (spider) central nervous system. This account details the features of these structures, which form a beltlike reticulum that is more complex than the simple linear tight junctions hitherto found in invertebrate tissues and which bear many of the characteristics of vertebrate zonulae occludentes. We also provide evidence that these junctions form the basis of a permeability barrier to exogenous compounds. In thin sections, the tight junctions are identifiable as punctate points of membrane apposition; they are seen to exclude the stain and appear as election- lucent moniliform strands along the lines of membrane fusion in en face views of uranyl-calcium-treated tissues. In freeze-fracture replicas, the regions of close membrane apposition exhibit P-face (PF) ridges and complementary E-face (EF) furrows that are coincident across face transitions, although slightly offset with respect to one another. The free inward diffusion of both ionic and colloidal lanthanum is inhibited by these punctate tight junctions so that they appear to form the basis of a circumferential blood-brain barrier. These results support the contention that tight junctions exist in the tissues of the invertebrata in spite of earlier suggestions that (a) they are unique to vertebrates and (b) septate junctions are the equivalent invertebrate occluding structure. The component tight junctional 8- to 10-nm-particulate PF ridges are intimately intercalated with, but clearly distinct from, inverted gap junctions possessing the 13-nm EF particles typical of arthropods. Hence, no confusion can occur as to which particles belong to each of the two junctional types, as commonly happens with vertebrate tissues, especially in the analysis of developing junctions. Indeed, their coexistance in this way supports the idea, over which there has been some controversy, that the intramembrane particles making up these two junctional types must be quite distinct entities rather than products of a common precursor.
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43
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Wood RL, Kuda AM. Formation of junctions in regenerating hydra: septate junctions. JOURNAL OF ULTRASTRUCTURE RESEARCH 1980; 70:104-17. [PMID: 7351691 DOI: 10.1016/s0022-5320(80)90026-x] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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44
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Johnston IS. The Ultrastructure of Skeletogenesis in Hermatypic Corals. INTERNATIONAL REVIEW OF CYTOLOGY 1980. [DOI: 10.1016/s0074-7696(08)62429-8] [Citation(s) in RCA: 135] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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45
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Green LF, Bergquist PR, Bullivant S. The structure and function of the smooth septate junction in a transporting epithelium: the Malpighian tubules of the New Zealand glow-worm Arachnocampa luminosa. Tissue Cell 1980; 12:365-81. [PMID: 7414600 DOI: 10.1016/0040-8166(80)90011-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Junctional complexes between the epithelial cells in the four distinct regions of the glow-worm Malpighian tubule were investigated by electron microscopy using thin sectioning, freeze-fracturing, osmotic disruption and tracer techniques. The lateral plasma membranes of all four cell types are joined by smooth septate junctions but the extent of the complex across the cell depth varies in the four different regions. The width of the septa, the interseptal spacing and the separation between the outer leaflets of the adjacent plasma membranes are different for each cell type. Gap junctions were identified only in the junctional complex between Type IV cells and were intercalated amongst large lateral sinuses. In oblique sections of lanthanum infiltrated tissue, the electron-lucent septa at the basal side of the junction are outlined by the tracer as it penetrates. In the junctional complexes of all four regions the septa appear as short, distinct, linear bars. In tangential sections of gap junctions between Type IV cells, the junctions appear as a hexagonal array of intermembrane particles with a centre to centre spacing of 18 nm. Horseradish peroxidase did not penetrate the junctional complexes very far but readily passed through the basal lamina into the spaces between extracellular invaginations of the basement membrane of the cells. Junctional complexes in all four areas of the tubule have similar freeze-fracture faces. In freeze-fracture replicas of fixed tissue continuous ridges of fused particles are seen on the P face and complementary furrows are found on the E face. Junctional response to osmotically adjusted Ringer solutions was similar in all four cell types. Distortion or 'blistering' of the intercellular space between between the septa of the unction occurred when the tissue was bathed in or injected with a hypertonic Ringer solution. The structure of these junctions, visualized by the different techniques, and the role of the septate junction in a transporting epithelium, are discussed.
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46
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Beadle DJ, Megaw MW. Intercellular junctions in the hypodermis, salivary gland and Gené's organ of the cattle tick, Boophilus microplus. Cell Tissue Res 1979; 202:119-24. [PMID: 509494 DOI: 10.1007/bf00239224] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The intercellular junctions that occur in the hypodermis, Gené's organ, and the salivary glands of the tick, B. microplus, are described. The epithelial cells of the hypodermis are connected by spot desmosomes and septate junctions and the secretory cells of Gené's organ by septate and gap junctions. The cap cells in the alveoli of the salivary gland connect to adjacent cells by gap junctions, hemidesmosomes and septate junctions into which microtubules are inserted.
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47
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Green CR, Bergquist PR, Bullivant S. An anastomosing septate junction in endothelial cells of the phylum echinodermata. JOURNAL OF ULTRASTRUCTURE RESEARCH 1979; 68:72-80. [PMID: 458934 DOI: 10.1016/s0022-5320(79)90143-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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48
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Abstract
Occluding junctions have been found between the lateral cell borders at the base of the rectum of Periplaneta americana. They appear as punctate membrane appositions in thin sections, and after incubation in physiological solutions containing lanthanum before fixation the inward penetration of tracer is impeded in this same basal area. Moreover, freeze-fracture studies of this region reveal simple linear ridges on fracture face P and grooves on fracture face E, which are similar to the less complex vertebrate tight junctions. The luminal clefts, which permit free inward diffusion of tracers, present no tight junctions, but do have septate junctions. These results support the contention that, contrary to earlier speculation, arthropods do possess tight junctions; these, rather than septate junctions, appear to form the morphological basis of at least some of the permeability barriers observed in invertebrates.
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49
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Lane NJ, Swales LS. Changes in the blood-brain barrier of the central nervous system in the blowfly during development, with special reference to the formation and disaggregation of gap and tight junctions. I. Larval development. Dev Biol 1978; 62:389-414. [PMID: 627311 DOI: 10.1016/0012-1606(78)90224-5] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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50
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Connell CJ. A freeze-fracture and lanthanum tracer study of the complex junction between Sertoli cells of the canine testis. J Cell Biol 1978; 76:57-75. [PMID: 618898 PMCID: PMC2109966 DOI: 10.1083/jcb.76.1.57] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
What appear to be true septate junctions by all techniques currently available for the cytological identification of intercellular junctions are part of a complex junction that interconnects the Sertoli cells of the canine testis. In the seminiferous epithelium, septate junctions are located basal to belts of tight junctions. In thin sections, septate junctions appear as double, parallel, transverse connections or septa spanning an approximately 90-A intercellular space between adjacent Sertoli cells. In en face sections of lanthanum-aldehyde-perfused specimens, the septa themselves exclude lanthanum and appear as electron-lucent lines arranged in a series of double, parallel rows on a background of electron-dense lanthanum. In freeze-fracture replicas this vertebrate septate junction appears as double, parallel rows of individual or fused particles which conform to the distribution of the intercellular septa. Septate junctions can be clearly distinguished from tight junctions as tight junctions prevent the movement of lanthanum tracer toward the lumen, appear as single rows of individual or fused particles in interlacing patterns within freeze-fracture replicas, and are seen as areas of close membrane apposition in thin sections. Both the septate junction and the tight junction are associated with specializations of the Sertoli cell cytoplasm. This is the first demonstration in a vertebrate tissue of a true septate junction.
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