scholarly journals THE STRUCTURAL ORGANIZATION OF THE SEPTATE AND GAP JUNCTIONS OF HYDRA

1972 ◽  
Vol 52 (2) ◽  
pp. 397-408 ◽  
Author(s):  
Arthur R. Hand ◽  
Stephen Gobel
Keyword(s):  
Gap Junctions ◽  
Intercellular Space ◽  
Structural Organization ◽  
Barrier Properties ◽  
Ruthenium Red ◽  
Septate Junction ◽  
Intercellular Coupling ◽  
Lanthanum Hydroxide ◽  
Septate Junctions ◽  
Large Numbers

The septate junctions and gap junctions of Hydra were studied utilizing the extracellular tracers lanthanum hydroxide and ruthenium red. Analysis of the septate junction from four perspectives has shown that each septum consists of a single row of hexagons sharing common sides of 50–60 A. Each hexagon is folded into chair configuration. Two sets of projections emanate from the corners of the hexagons. One set (A projections) attaches the hexagons to the cell membranes at 80–100-A intervals, while the other set (V projections) joins some adjacent septa to each other. The septate junctions generally contain a few large interseptal spaces and a few septa which do not extend the full length of the junction. Basal to the septate junctions the cells in each layer are joined by numerous gap junctions. Gap junctions also join the muscular processes in each layer as well as those which connect the layers across the mesoglea. The gap junctions of Hydra are composed of rounded plaques 0.15–0.5 µ in diameter which contain 85-A hexagonally packed subunits. Each plaque is delimited from the surrounding intercellular space by a single 40-A band. Large numbers of these plaques are tightly packed, often lying about 20 A apart. This en plaque configuration of the gap junctions of Hydra contrasts with their sparser, more widely separated distribution in many vertebrate tissues. These studies conclude that the septate junction may possess some barrier properties and that both junctions are important in intercellular adhesion. On a morphological basis, the gap junction appears to be more suitable for intercellular coupling than the septate junction.

Topographical variations in the structure of the smooth septate junction

1979 ◽  
Vol 37 (1) ◽  
pp. 373-389
Author(s):  
H.B. Skaer ◽  
J.B. Harrison ◽  
W.M. Lee
Keyword(s):  
Musca Domestica ◽  
Functional Significance ◽  
Freeze Fracture ◽  
Rhodnius Prolixus ◽  
Malpighian Tubules ◽  
Septate Junction ◽  
Lanthanum Hydroxide ◽  
Septate Junctions ◽  
Standard Fixation

Smooth septate junctions in the midgut of Musca domestica and in Malpighian tubules of both Musca and Rhodnius prolixus are described. Details of the structures revealed after standard fixation, fixation in the presence of the stain, lanthanum hydroxide, and after freeze-fracture are discussed in the light of models previously put forward to explain the interrelations of the images obtained by these different methods. The organization of the junction between cells of the midgut varies in the apical-to-basal axis. At the apical border the septa (or ridges in freeze-fracture replicas) are packed tightly and follow an undulating but strictly parallel course. This packing loosens towards the middle of the junction until, at its basal extremity, the septa (ridges in replicas) are widely separated and follow independent meandering courses. That these features are found both in lanthanum-infiltrated specimens and freeze-fracture replicas allows a correlation to be made between the septa and the freeze-fracture ridges. The functional significance of these smooth septate junctions is discussed.

Evidence for septate junctions in the syzygy of the protozoon Gregarina polymorpha (Protozoa, Apicomplexa)

1988 ◽  
Vol 89 (2) ◽  
pp. 217-224
Author(s):  
ROMANO DALLAI ◽  
MARIA VEGNI TALLURI
Keyword(s):  
Plasma Membrane ◽  
Intercellular Space ◽  
Plasma Membranes ◽  
Freeze Fracture ◽  
Septate Junction ◽  
Fracture Face ◽  
Septate Junctions ◽  
Thin Sections ◽  
Intramembranous Particles ◽  
Lanthanum Tracer

A septate junction is described in reproductive pairs of the protozoon Gregarina polymorpha, using conventional thin sections, lanthanum tracer and freeze-fracture techniques. The septate junction is established between the plasma membranes at the tips of the joined epicytic folds. It is characterized by an intercellular space of 14–17 nm traversed by septa with a repeat of 15–25 nm. Lanthanum-treated material exhibits transparent curves forming a meshwork. Freeze-fracture replicas show membrane modifications in the shape of short rows of intramembranous particles on the E fracture face of the plasma membrane. The significance of the finding of such a septate junction between protozoan cells is discussed.

scholarly journals COEXISTENCE OF GAP AND SEPTATE JUNCTIONS IN AN INVERTEBRATE EPITHELIUM

1971 ◽  
Vol 50 (1) ◽  
pp. 92-101 ◽  
Author(s):  
A. J. Hudspeth ◽  
J. P. Revel
Keyword(s):  
Electron Microscope ◽  
Gap Junctions ◽  
Gap Junction ◽  
Extracellular Space ◽  
Intercellular Junctions ◽  
Septate Junction ◽  
High Electron ◽  
Septate Junctions ◽  
Electrotonic Coupling ◽  
Lanthanum Tracer

The intercellular junctions of the epithelium lining the hepatic caecum of Daphnia were examined. Electron microscope investigations involved both conventionally fixed material and tissue exposed to a lanthanum tracer of the extracellular space. Both septate junctions and gap junctions occur between the cells studied. The septate junctions lie apically and resemble those commonly discerned between cells of other invertebrates. They are atypical in that the high electron opacity of the extracellular space obscures septa in routine preparations. The gap junctions are characterized by a uniform 30 A space between apposed cell membranes. Lanthanum treatment of gap junctions reveals an array of particles of 95 A diameter and 120 A separation lying in the plane of the junction. As this pattern closely resembles that described previously in vertebrates, it appears that the gap junction is phylogenetically widespread. In view of evidence that the gap junction mediates intercellular electrotonic coupling, the assignment of a coupling role to other junctions, notably the septate junction, must be questioned wherever these junctions coexist.

Isolation and characterization of invertebrate smooth septate junctions

1983 ◽  
Vol 62 (1) ◽  
pp. 351-370
Author(s):  
C.R. Green ◽  
C. Noirot-Timothee ◽  
C. Noirot
Keyword(s):  
Molecular Weight ◽  
Gap Junctions ◽  
Freeze Fracture ◽  
Intercellular Junctions ◽  
Septate Junction ◽  
Major Protein ◽  
Septate Junctions ◽  
Isolation And Characterization ◽  
Significant Difference ◽  
Freeze Fracture Electron Microscopy

Using modifications of techniques used for the isolation of macula type intercellular junctions (gap junctions and desmosomes) the arthropod smooth septate junction has been isolated from insect midgut tissue. Midguts from cockroaches or mealworms were used and membrane fractions were obtained by sucrose gradient and ultracentrifugation techniques. Preparations with reasonable concentrations of septate junction were obtained and have been studied by thin-section, negative-stain and freeze-fracture electron microscopy. The junctions appeared to be well preserved, although there was evidence that the junction strands were able to slide within the plane of the membrane. Septa were seen to have a cross-striated appearance when viewed after negative staining but their exact structure remained difficult to determine. Polyacrylamide gel electrophoretic studies demonstrated the reproducibility of the isolation procedure and showed that septa may have a 47 000 molecular weight glycoprotein component. Gel electrophoresis also gave some indication of the intramembrane biochemistry of the smooth septate junction, with proteins of 31 000 and 32 000 molecular weight always occurring in the junction fractions. The junctions were, however, very sensitive to both mechanical and chemical treatments, the septa were destroyed by rough homogenization or by treatment with urea at a concentration as low as 1 M. Freeze-fracture of untreated, isolated junctions demonstrated no differences from junctions in intact tissue, while replicas of urea-treated material were more difficult to interpret as the component parts of the junctions became separated once the septa had been destroyed. Gap junctions were also obtained and resisted both mechanical and chemical treatment, which destroyed the septate junctions. Their major protein component appeared to have a molecular weight of 36 000. Attempts to isolate pleated septate junctions (from insects, molluscs and annelids) by the same techniques failed, implying a significant difference in the structures of the two types of septate junction.

Gap and septate junctions in the excitable endoderm of Polyorchis penicillatus (Hydrozoa, Anthomedusae)

1979 ◽  
Vol 36 (1) ◽  
pp. 391-400
Author(s):  
M.G. King ◽  
A.N. Spencer
Keyword(s):  
Epithelial Cells ◽  
Action Potential ◽  
Gap Junctions ◽  
Intercellular Space ◽  
Septate Junctions ◽  
Impulse Conduction ◽  
Polyorchis Penicillatus ◽  
Morphological Basis ◽  
En Face ◽  
Electron Lucent

The morphological basis of impulse conduction in a jellyfish epithelium was investigated. Lanthanum impregnation of endodermal canal and endodermal lamella verified the existence of true gap junctions in Polyorchis. In both transverse and en face sections of gap junctions, electron-lucent globules, with a width of 7–8 nm and a spacing of about 11 nm, are evident. Gap-junctions are concentrated at the peripheral canal margin and septate junctions are localized around the canal lumen. Epithelial cells of the endodermal canals are capable of conducting a non-decrementing action potential. It is suggested that endodermal spike propagation, which can mediate ‘crumpling’ behaviour, is dependent upon low-resistence ionic pathways provided by gap-junctions and upon sealing of the intercellular space from saline extracellular fluids by septate junctions.

Developmental Regulation and Structural Organization of Connexins in Epidermal Gap Junctions

1994 ◽  
Vol 164 (1) ◽  
pp. 183-196 ◽  
Author(s):  
Boris Risek ◽  
F.George Klier ◽  
Norton B. Gilula
Keyword(s):  
Gap Junctions ◽  
Structural Organization ◽  
Developmental Regulation

Polypeptide composition and organization of the sea urchin extraembryonic hyaline layer

1990 ◽  
Vol 68 (9) ◽  
pp. 1083-1089 ◽  
Author(s):  
John J. Robinson
Keyword(s):  
Embryonic Development ◽  
Sea Urchin ◽  
Organization Development ◽  
Structural Organization ◽  
Protein Composition ◽  
Ruthenium Red ◽  
Proteinase K ◽  
Polypeptide Composition ◽  
Layer Composition ◽  
Precipitable Protein

The protein composition and organization of the sea urchin extraembryonic hyaline layer was examined. Hyalin and a polypeptide of 45 kilodaltons (kDa) were present in hyaline layers isolated from 1-h-old embryos through to the pluteus larva stage. In contrast, several polypeptide species ranging in size from 175 to 32 kDa either decreased in amount or disappeared from the layer as embryonic development proceeded. Concomitant with the changes in composition, hyaline layers became progressively more refractory to dissolution by washing in Ca2+, Mg2+-free seawater. Incubation of intact layers, isolated from 1-h-old embryos, with proteinase K resulted in the selective digestion of hyalin and was accompanied by release of the 45-kDa polypeptide from the layers. Washing intact layers in 20 mM Tris (pH 8.0) also resulted in the selective removal of hyalin and the 45-kDa polypeptide. The Ca2+-precipitable protein hyalin, alone among the hyaline layer polypeptides, bound the Ca2+-antagonist ruthenium red. These results suggest a structural organization within the hyaline layer that is both heterogenous and dynamic throughout embryonic development.Key words: hyaline layer, composition, organization, development.

Morphology and ultrastructure of oral strains of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus

1980 ◽  
Vol 30 (2) ◽  
pp. 588-600
Author(s):  
S C Holt ◽  
A C Tanner ◽  
S S Socransky
Keyword(s):  
Electron Microscopy ◽  
Ruthenium Red ◽  
Actinobacillus Actinomycetemcomitans ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Large Numbers ◽  
Haemophilus Aphrophilus ◽  
Ruthenium Red Staining ◽  
Amorphous Surface ◽  
Scanning Electron

Selected human oral and nonoral strains of the genera Actinobacillus and Haemophilus were examined by transmission and scanning electron microscopy. The strains examined were morphologically identical to recognized Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus, and Haemophilus paraphrophilus. By transmission electron microscopy, the cells were typically gram negative in morphology, with several strains possessing some extracellular ruthenium red-staining polymeric material. Numerous vesicular structures, morphologically identical to lipopolysaccharide vesicles, were seen to originate from and be continuous with the surface of the outer membrane. Large numbers of these vesicles were also found in the external environment. Scanning electron microscopic observations revealed that both actinobacilli and haemophili possessed surface projections and an amorphous surface material which connected and covered adjacent cells.

Isolation and biochemical characterization of septate junctions: differences between the proteins in smooth and pleated varieties

1989 ◽  
Vol 93 (1) ◽  
pp. 123-131
Author(s):  
NANCY J. LANE ◽  
STEPHEN M. DILWORTH
Keyword(s):  
Periplaneta Americana ◽  
Biochemical Characterization ◽  
Septate Junction ◽  
Septate Junctions ◽  
Molecular Weights ◽  
Thin Sectioning ◽  
Sds Page ◽  
High Concentrations ◽  
Membrane Components

Septate junctions are found only in invertebrate tissues, and are almost ubiquitous within them. In arthropods, the two major types are the ‘pleated’ and the ‘smooth’ varieties. Using tissues from different species, including the cockroach Periplaneta americana, procedures have been established for obtaining membrane fractions selectively enriched in septate junctions. The junctions have been identified in pellets of these fractions by both thin sectioning and freeze-fracturing. SDS-PAGE of these membrane fractions reveals two major polypeptide species with apparent molecular weights of 22000–24000 and 17000–18000. Consistent differences in these apparent molecular weights are observed between the pleated and smooth varieties of septate junction. These polypeptides are probably integral membrane components, as they remain associated after treatment with high concentrations of urea. Evidence suggests a plane of weakness in the mid-line of the extracellular septal ribbons.

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