scholarly journals On the structural organization of isolated bovine lens fiber junctions.

1982 ◽  
Vol 93 (1) ◽  
pp. 175-189 ◽  
Author(s):  
G Zampighi ◽  
S A Simon ◽  
J D Robertson ◽  
T J McIntosh ◽  
M J Costello
Keyword(s):  
Gap Junctions ◽  
Lipid Bilayers ◽  
Freeze Fracture ◽  
Apparent Molecular Weight ◽  
Surface Topology ◽  
Square Lattice ◽  
Lens Fiber ◽  
Fiber Cells ◽  
Junction Protein ◽  
Freeze Fracture Electron Microscopy

Junctions between fiber cells of bovine lenses have been isolated in milligram quantities, without using detergents or proteases. The structure of the isolated junctions has been studied by thin-section, negative-stain, and freeze-fracture electron microscopy and by x-ray diffraction. The junctions are large and most often have an undulating surface topology as determined by thin sectioning and freeze-fracture. These undulations resemble the tongue-and-groove interdigitations between lens fiber cells previously seen by others (D. H. Dickson and G. W. Crock, 1972, Invest. Ophthalmol. 11:809-815). In sections, the isolated junctions display a pentalamellar structure approximately 13-14 nm in overall thickness, which is significantly thinner than liver gap junctions. Each junctional membrane contains in the plane of the lipid bilayers distinct units arranged in a square lattice with a center-to-center spacing of 6.6 nm. Freeze-fracture replicas of the junctions fractured transversely show that the repeating units extend across the entire thickness of each membrane. Each unit is probably constructed from four identical subunits, with each subunit containing a protein of an apparent molecular weight of 27,000. We conclude that the lens junctions are structurally and chemically, different from gap junctions and could represent a new kind of intercellular contact, not simply another crystalline state of the gap junction protein.

Calmodulin-mediated gating of lens gap junction channels in vesicles

1984 ◽  
Vol 42 ◽  
pp. 134-137
Author(s):  
Camillo Peracchia ◽  
Stephen J. Girsch
Keyword(s):  
Gap Junctions ◽  
Freeze Fracture ◽  
Orthogonal Arrays ◽  
Eye Lens ◽  
Lens Fiber ◽  
Cell Coupling ◽  
Particle Spacing ◽  
Fiber Cells ◽  
Gap Junction Channels ◽  
Communicating Junctions

The fiber cells of eye lens communicate directly with each other by exchanging ions, dyes and metabolites. In most tissues this type of communication (cell coupling) is mediated by gap junctions. In the lens, the fiber cells are extensively interconnected by junctions. However, lens junctions, although morphologically similar to gap junctions, differ from them in a number of structural, biochemical and immunological features. Like gap junctions, lens junctions are regions of close cell-to-cell apposition. Unlike gap junctions, however, the extracellular gap is apparently absent in lens junctions, such that their thickness is approximately 2 nm smaller than that of typical gap junctions (Fig. 1,c). In freeze-fracture replicas, the particles of control lens junctions are more loosely packed than those of typical gap junctions (Fig. 1,a) and crystallize, when exposed to uncoupling agents such as Ca++, or H+, into pseudo-hexagonal, rhombic (Fig. 1,b) and orthogonal arrays with a particle-to-particle spacing of 6.5 nm. Because of these differences, questions have been raised about the interpretation of the lens junctions as communicating junctions, in spite of the fact that they are the only junctions interlinking lens fiber cells.

scholarly journals Comparative analysis of the major polypeptides from liver gap junctions and lens fiber junctions.

1982 ◽  
Vol 92 (1) ◽  
pp. 53-59 ◽  
Author(s):  
E L Hertzberg ◽  
D J Anderson ◽  
M Friedlander ◽  
N B Gilula
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Peptide Mapping ◽  
Freeze Fracture ◽  
Apparent Molecular Weight ◽  
Lens Fiber ◽  
Physiological Properties ◽  
Thin Section Electron Microscopy ◽  
Section Electron ◽  
Section Electron Microscopy

Gap junctions from rat liver and fiber junctions from bovine lens have similar septilaminar profiles when examined by thin-section electron microscopy and differ only slightly with respect to the packing of intramembrane particles in freeze-fracture images. These similarities have often led to lens fiber junctions being referred to as gap junctions. Junctions from both sources were isolated as enriched subcellular fractions and their major polypeptide components compared biochemically and immunochemically. The major liver gap junction polypeptide has an apparent molecular weight of 27,000, while a 25,000-dalton polypeptide is the major component of lens fiber junctions. The two polypeptides are not homologous when compared by partial peptide mapping in SDS. In addition, there is not detectable antigenic similarity between the two polypeptides by immunochemical criteria using antibodies to the 25,000-dalton lens fiber junction polypeptide. Thus, in spite of the ultrastructural similarities, the gap junction and the lens fiber junction are comprised of distinctly different polypeptides, suggesting that the lens fiber junction contains a unique gene product and potentially different physiological properties.

Ultrastructural analysis of the apical ectodermal ridge during vertebrate limb morphogenesis

Development ◽  
1977 ◽  
Vol 41 (1) ◽  
pp. 223-232
Author(s):  
John F. Fallon ◽  
Robert O. Kelley
Keyword(s):  
Electron Microscopy ◽  
Gap Junctions ◽  
Freeze Fracture ◽  
Apical Ectodermal Ridge ◽  
Structural Requirements ◽  
Limb Morphogenesis ◽  
Vertebrate Limb ◽  
The Difference ◽  
Freeze Fracture Electron Microscopy ◽  
Fracture Electron

The fine structure of the apical ectodermal ridge of five phylogenetically divergent orders of mammals and two orders of birds was examined using transmission and freeze fracture electron microscopy. Numerous large gap junctions were found in all apical ectodermal ridges studied. This was in contrast to the dorsal and ventral limb ectoderms where gap junctions were always very small and sparsely distributed. Thus, gap junctions distinguish the inductively active apical epithelium from the adjacent dorsal and ventral ectoderms. The distribution of gap junctions in the ridge was different between birds and mammals but characteristic within the two classes. Birds, with a pseudostratified columnar apical ridge, had the heaviest concentration of gap junctions at the base of each ridge cell close to the point where contact was made with the basal lamina. Whereas mammals, with a stratified cuboidal to squamous apical ridge, had a more uniform distribution of gap junctions throughout the apical epithelium. The difference in distribution for each class may reflect structural requirements for coupling of cells in the entire ridge. We propose that all cells of the apical ridges of birds and mammals are electrotonically and/or metabolically coupled and that this may be a requirement for the integrated function of the ridge during limb morphogenesis.

The occurrence of lipidic particles in lipid bilayers as seen by 31P NMR and freeze-fracture electron-microscopy

1979 ◽  
Vol 555 (2) ◽  
pp. 200-209 ◽  
Author(s):  
B. De Kruijff ◽  
A.J. Verkley ◽  
C.J.A. Van Echteld ◽  
W.J. Gerritsen ◽  
C. Mombers ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Lipid Bilayers ◽  
31P Nmr ◽  
Freeze Fracture ◽  
Freeze Fracture Electron Microscopy ◽  
Fracture Electron

The syneretic lens junction

1984 ◽  
Vol 42 ◽  
pp. 16-19
Author(s):  
J. David Robertson ◽  
M.J. Costello ◽  
T.J. McIntosh
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Cell Membranes ◽  
Freeze Fracture ◽  
Enzymatic Digestion ◽  
Fiber Cell ◽  
Intermembrane Space ◽  
Minor Components ◽  
Thin Sections ◽  
Fiber Cells

The lens of the eye consists of closely adherent greatly elongated flattened narrow fiber cells that are electrically coupled by gap junctions. In thin sections the 100-150 Å intermembrane space usually seen in tissues between adjacent cells is greatly reduced between adjacent fiber cells. Freeze-fracture-etch (FFE) studies have demonstrated gap junctions between fiber cells. Several workers have observed expanses of square crystallinity in fiber cell membranes with a lattice constant of 6-7 nm. This has usually been attributed variously to artifact induced by calcium, pH or proteolytic enzymatic digestion. Square arrays have been seen in isolated fractions of fiber cell membranes prepared with detergents as minor components and dismissed as relatively insignificant and either related or unrelated to gap junctions. Some have regarded them as a form of gap junction.

Intercellular communication between epithelial and fiber cells of the eye lens

1994 ◽  
Vol 107 (4) ◽  
pp. 799-811 ◽  
Author(s):  
S. Bassnett ◽  
J.R. Kuszak ◽  
L. Reinisch ◽  
H.G. Brown ◽  
D.C. Beebe
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Freeze Fracture ◽  
Cell Types ◽  
Lens Epithelium ◽  
Fiber Cell ◽  
Fracture Plane ◽  
Metabolic Cooperation ◽  
Fiber Cells ◽  
Resistance Pathway

Results of electrical, dye-coupling and morphological studies have previously suggested that gap junctions mediate communication between the anterior epithelium of the lens and the underlying lens fiber cells. This connection is believed to permit ‘metabolic cooperation’ between these dissimilar cell types and may be of particular importance to the fiber cells, which are thought incapable of autonomous ionic homeostasis. We reinvestigated the nature of the connection between epithelial and fiber cells of the embryonic chicken lens using fluorescence confocal microscopy and freeze-fracture analysis. In contrast to earlier studies, our data provided no support for gap-junction-mediated transport from the lens epithelium to the fibers. Fluorescent dyes loaded biochemically into the lens epithelium were retained there for more than one hour. There was a decrease in epithelial fluorescence over this period, but this was not accompanied by an increase in fiber cell fluorescence. Diffusional modeling suggested that these data were inconsistent with the presence of extensive epithelium-fiber cell coupling, even if the observed decrease in epithelial fluorescence was attributed exclusively to the diffusion of dye into the fiber mass via gap junctions. Furthermore, the rate of loss of fluorescence from isolated epithelia was indistinguishable from that measured in whole lenses, suggesting that decreased epithelial fluorescence resulted from photobleaching and leakage of dye rather than diffusion, via gap junctions, into the fibers. Analysis of freeze-fracture replicas of plasma membranes at the epithelial-fiber cell interface failed to reveal evidence of gap-junction plaques, although evidence of endocytosis was abundant. These studies were done under conditions where the location of the fracture plane was unambiguous and where gap junctions could be observed in the lateral membranes of neighboring epithelial and fiber cells. Paradoxically, tracer molecules injected into the fiber mass were able to pass into the epithelium via a pathway that was not blocked by incubation at 4 degrees C or by treatment with octanol and which excluded large (approximately 10 kDa) molecular mass tracers. Together with previous measurements of electrical coupling between fiber cells and epithelial cells, these data indicate the presence of a low-resistance pathway connecting these cell types that is not mediated by classical gap junctions.

Synthesis and assembly of human beta 1 gap junctions in BHK cells by DNA transfection with the human beta 1 cDNA

1995 ◽  
Vol 108 (12) ◽  
pp. 3725-3734 ◽  
Author(s):  
N.M. Kumar ◽  
D.S. Friend ◽  
N.B. Gilula
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Freeze Fracture ◽  
Growth Control ◽  
Double Membrane ◽  
Correct Orientation ◽  
Junctional Communication ◽  
Junction Protein ◽  
Particle Aggregates ◽  
Metallothionein Promoter

Gap junctional communication is important in many physiological processes, including growth control, patterning, and the synchronization of cell-to-cell activities. It has been difficult to study the synthesis and assembly of gap junctions due to their low abundance. To overcome this limitation, baby hamster kidney cells (BHK) have been transfected with a human beta 1 (Cx32) connexin cDNA construct. Expression was placed under the control of the mouse metallothionein promoter that can be induced by heavy metals. The transfected cells were characterized by DNA, RNA and protein analysis, as well as by scrape loading to detect functional channels. Functional beta 1 connexin was detected only in cells transfected with beta 1 connexin cDNA in the correct orientation (beta 1-BHK). Analysis of the cells by light microscopic immunocytochemistry indicated that beta 1 connexin antigen was localized to the plasma membrane and to several intracellular compartments. Characterization with thin section electron microscopy revealed extensive areas of assembled double membrane gap junctions between cells (on the cell surface), in the endoplasmic reticulum (ER), and the nuclear envelope. This unusual intracellular distribution for assembled gap junction protein was confirmed by freeze fracture analysis, which revealed large particle aggregates, characteristic of gap junction plaques, on the fracture faces of all these membranes. The presence of gap junction particle aggregates in the ER suggests that the oligomerization of connexin can occur at its site of synthesis. Further, the process of assembly into double membrane junction structures in intracellular membranes may be driven by connexin protein concentration.

scholarly journals Preparation of a gap junction fraction from uteri of pregnant rats: the 28-kD polypeptides of uterus, liver, and heart gap junctions are homologous.

1985 ◽  
Vol 101 (4) ◽  
pp. 1363-1370 ◽  
Author(s):  
A S Zervos ◽  
J Hope ◽  
W H Evans
Keyword(s):  
Plasma Membrane ◽  
Gap Junctions ◽  
Gap Junction ◽  
Apparent Molecular Weight ◽  
Antigenic Determinants ◽  
Pregnant Rats ◽  
Thin Sections ◽  
Amino Terminal ◽  
Junction Protein ◽  
Gap Junction Protein

A procedure for the preparation of a gap junction fraction from the uteri of pregnant rats is described. The uterine gap junctions, when examined by electron microscopy of thin sections and in negatively stained preparations, were similar to gap junctions isolated from heart and liver. Major proteins of similar apparent molecular weight (Mr 28,000) were found in gap junction fractions isolated from the uterus, heart, and liver, and were shown to have highly homologous structures by two-dimensional mapping of their tryptic peptides. An Mr 10,000 polypeptide, previously deduced to be a proteolytic product of the Mr 28,000 polypeptide of rat liver (Nicholson, B. J., L. J. Takemoto, M. W. Hunkapiller, L. E. Hood, and J.-P. Revel, 1983, Cell, 32:967-978), was also studied and shown by chymotryptic mapping to be homologous in the uterine, heart, and liver gap junction fractions. An antibody raised in rabbits to a synthetic peptide corresponding to an amino-terminal sequence of the liver gap junction protein recognized Mr 28,000 proteins in the three tissues studied, showing that the proteins shared common antigenic determinants. These results indicate that gap junctions are biochemically conserved plasma membrane specializations. The view that gap junctions are tissue-specific plasma membrane organelles based on previous comparisons of Mr 26,000-30,000 polypeptides is not sustained by the present results.

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