scholarly journals Unusual structural features and assembly of gap and pleated septate junctions in embryonic cockroach CNS

1985 ◽  
Vol 76 (1) ◽  
pp. 269-281
Author(s):  
L.S. Swales ◽  
N.J. Lane
Keyword(s):  
Gap Junctions ◽  
Tight Junctions ◽  
Glial Cell ◽  
Structural Features ◽  
Septate Junctions ◽  
Intramembrane Particles ◽  
Cell Processes ◽  
Gap Junctional ◽  
Perineurial Cells

Junctional assembly in the developing CNS in cockroach embryos has been studied during the last half of neurogenesis. Atypical linear tracts of gap junctions are found to develop between attenuated cytoplasmic glial cell processes and their overlying perineurial cells during the last third of development. During both perineurial and glial gap-junctional formation, 13 nm E face (EF) intramembrane particles (IMPs), such as are characteristic of arthropod gap junctions, are seen initially as free IMPs; these then become arranged in loose irregular clusters or alignments and finally are aggregated in plaques. P face ridges (or EF grooves), typical of tight junctions, are found on the same perineurial membrane face as assembling gap-junctional PF pits (or EF particles). Pleated separate junctions also develop between adjacent perineurial processes during the last third of embryogenesis; these form by the apparent migration of individual 8 nm PF IMPs into meandering rows, which then become aligned in numerous orderly parallel stacks. Although all these junctions occur on the same perineurial membrane face, the IMPs that form the different junctional types never appear to be confused during junctional assembly. The cues to signal the advent of these precise patterns, however, are unknown.

Tight and gap junctions in the intestinal tract of tunicates (Urochordata): a freeze-fracture study

1986 ◽  
Vol 84 (1) ◽  
pp. 1-17
Author(s):  
N.J. Lane ◽  
R. Dallai ◽  
P. Burighel ◽  
G.B. Martinucci
Keyword(s):  
Gap Junctions ◽  
Tight Junctions ◽  
Thin Section ◽  
Intestinal Tract ◽  
Freeze Fracture ◽  
Intestinal Cells ◽  
Fracture Profile ◽  
Tracer Studies ◽  
Septate Junctions ◽  
Fracture Study

The intestinal tracts from seven different species of tunicates, some solitary, some colonial, were studied fine-structurally by freeze-fracture. These urochordates occupy an intermediate position phylogenetically between the vertebrates and the invertebrates. The various regions of their gut were isolated for examination and the junctional characteristics of each part investigated. All the species examined exhibited unequivocal vertebrate-like belts of tight-junctional networks at the luminal border of their intestinal cells. No septate junctions were observed. The tight junctions varied in the number of their component strands and the depth to which they extended basally, some becoming loose and fragmented towards that border. The junctions consisted of ridges or rows of intramembranous particles (IMPs) on the P face, with complementary, but offset, E face grooves into which IMPs sometimes fractured. Tracer studies show that punctate appositions, the thin-section correlate of these ridge/groove systems, are sites beyond which exogenous molecules do not penetrate. These junctions are therefore likely to represent permeability barriers as in the gut tract of higher chordates. Associated with these occluding zonular junctions are intermediate junctions, which exhibit no identifiable freeze-fracture profile, and macular gap junctions, characterized by a reduced intercellular cleft in thin section and by clustered arrays of P face particles in freeze-fractured replicas; these display complementary aggregates of E face pits. The diameters of these maculae are rarely very large, but in certain species (for example, Ciona), they are unusually small. In some tissues, notably those of Diplosoma and Botryllus, they are all of rather similar size, but very numerous. In yet others, such as Molgula, they are polygonal with angular outlines, as might be indicative of the uncoupled state. In many attributes, these various junctions are more similar to those found in the tissues of vertebrates, than to those in the invertebrates, which the adult zooid forms of these lowly chordates resemble anatomically.

Development of Intercellular Junctions in the Vestibular End-Organ

1984 ◽  
Vol 93 (1) ◽  
pp. 89-95 ◽  
Author(s):  
Dan Bagger-Sjöbäck ◽  
Matti Anniko
Keyword(s):  
Gap Junctions ◽  
Inner Ear ◽  
Tight Junctions ◽  
Hair Cells ◽  
Intercellular Junctions ◽  
Supporting Cells ◽  
Fluid Compartments ◽  
Well Differentiated ◽  
Gap Junctional ◽  
Perilymphatic Space

The intercellular junctions and the tight junctions in particular are considered to be of great importance for the function of the inner ear. The two fluid compartments of the inner ear, the perilymphatic space and the endolymphatic space, need to be effectively separated from each other in order to maintain the ionic gradients between the two. The tight junctional structures have been described in mature animals of several species. In the present article the development and maturation of the intercellular junctions are described in the mouse embryo. Junctional elements are already present in the 12th gestational day otocyst. Over the next few days, the otocyst is differentiated into a cochlear portion and a vestibular portion. The tight junctions in the vestibular portion gradually attain their mature appearance. It seems as if the tight junctions of the supporting cells develop slightly faster than those of the hair cells. At the time of birth, all epithelial cells have obtained mature appearance. The tight junctions are fully developed on the supporting cells as well as the hair cells. Small gap junctions are present in the 14th gestational day specimens. Two days later the hair cells and the supporting cells are well differentiated; small to medium-sized gap junctions are present only on the supporting cells at this stage. At the time of birth larger gap junctional aggregates have developed on the supporting cells.

Cell relationships during aggregation between preimplantation embryos and teratocarcinoma-derived cells

Development ◽  
1984 ◽  
Vol 81 (1) ◽  
pp. 17-35
Author(s):  
E. Lehtonen ◽  
J. Wartiovaara ◽  
I. Reima
Keyword(s):  
Gap Junctions ◽  
Tight Junctions ◽  
Preimplantation Embryos ◽  
Aggregate Formation ◽  
Cell Stage ◽  
F9 Cells ◽  
Cell Processes ◽  
Ec Cells ◽  
Early Phases ◽  
Close Contacts

Cleavage-stage mouse embryos aggregate and form chimaeric blastocysts with embryonal carcinoma (EC) cells. We used scanning and transmission electron microscopy to study cell relationships during aggregate formation between 8-cell-stage embryos and F9 EC cells. Relations between heterotypic cells were similarly studied in aggregation experiments with embryos and teratocarcinoma-derived visceral (PSA5-E) and parietal (PYS-2) endoderm cells and in experiments with EC cells and endoderm cells. The embryos and F9 cells always adhered to each other and rapidly formed compacted aggregates. Numerous microvilli and cell processes, originating from both embryo and EC cells, extended between the two cell types during adhesion and early phases of aggregation. The aggregation process involved spreading of the blastomeres on the EC cells. Frequent adherent junctions and close contacts, including possible focal gap or tight junctions were observed between the embryo and F9 cells after 3 h of culture. Apparent gap or tight junctions were infrequent during the early phases of aggregation but during further culture, extensive typical gap junctions were also seen between embryo and EC cells. The embryos adhered only irregularly and loosely to PSA5-E and PYS-2 cells; this interaction never led to aggregate formation comparable to that seen in the experiments with embryos and EC cells. Close contacts but no gap or tight junctions could be observed between the embryo and endoderm cells. On the other hand, both PSA5-E and PYS-2 cells readily adhered to and aggregated with EC cells. The present results suggest that microvilli and cell processes mediate membrane interactions during adhesion and early phases of aggregation between embryos and EC cells. During aggregation, blastomeres spread over the EC cells, and rapid formation of adherent junctions and close contacts, including possible focal gap or tight junctions is involved during the early phases of this process. After this initial phase, typical gap junctions are also seen between the embryo and EC cells. Interestingly, adhesive properties of embryo and EC cells differ: the former aggregate only with EC cells, whereas the latter do so also with teratocarcinoma-derived visceral and parietal endoderm cells. Mechanisms operating in the morphogenetic movement of cells in this experimental setup may be involved also in the development of the blastocyst in vivo.

Gap junctions in the differentiated neural retinae of newly hatched chickens

1976 ◽  
Vol 22 (3) ◽  
pp. 597-606
Author(s):  
H. Fujisawa ◽  
H. Morioka ◽  
H. Nakamura ◽  
K. Watanabe
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Tight Junctions ◽  
Thin Section ◽  
Outer Nuclear Layer ◽  
Double Cone ◽  
Linear Arrays ◽  
Intramembrane Particles ◽  
Plexiform Layers ◽  
Membrane Region

Gap junctions in the neural retinae of newly hatched chickens were examined in thin section and by freeze cleaving. Unusual gap junctions containing linear arrays of intramembrane particles are found between principal and accessory cones which form a double cone at the region of the outer limiting membrane. These unusual gap junctions are often continuous with macular aggregates of hexagonally packed intramembrane particles which are characteristic of a typical gap junction. Typical gap junctions are also found in both the outer and the inner plexiform layers and in the outer nuclear layer, but are not so abundant as in the outer limiting membrane region. The sizes of intramembrane particles and their centre-to-centre spacing within the macular aggregate of a gap junction in differentiated neural retinae are slightly larger than those in undifferentiated neural retinae. Tight junctions are not found in differentiated neural retinae.

A New Junctional Structure in the Epithelia of Insects of the Order Dictyoptera

1972 ◽  
Vol 10 (3) ◽  
pp. 683-691
Author(s):  
N. E. FLOWER
Keyword(s):  
Epithelial Cells ◽  
Gap Junctions ◽  
Gap Junction ◽  
Tight Junctions ◽  
Hexagonal Array ◽  
Septate Junctions ◽  
New Type ◽  
Junctional Complexes ◽  
Junctional Structure

The junctional complexes in the epithelia of insects of the order Dictyoptera have been investigated using the freeze-etch technique. As well as septate junctions, a new type of junction has been identified and the name ‘inverted gap junction’ proposed. The patch-like distribution of the inverted gap junctions basal to and often closely associated with septate junctions is very similar to the form of gap junctions and their relationship to tight junctions in vertebrates. This suggests that the inverted gap junctions, like normal gap junctions, could perform a communicating function between epithelial cells. The following features distinguish inverted gap junctions from normal gap junctions in freeze-etch preparations: (i) the arrays of particles and holes within inverted gap junctions appear on B- and A-type faces respectively, i.e. on the opposite faces to the particles and holes in gap junctions; (ii) the particles within inverted gap junctions appear to lie in rows which anastomose to form an irregular net, and not in an hexagonal array, as occurs in gap junctions.

scholarly journals The principal neurons of the medial nucleus of the trapezoid body and NG2+ glial cells receive coordinated excitatory synaptic input

2009 ◽  
Vol 134 (2) ◽  
pp. 115-127 ◽  
Author(s):  
Jochen Müller ◽  
Daniel Reyes-Haro ◽  
Tatjyana Pivneva ◽  
Christiane Nolte ◽  
Roland Schaette ◽  
...  
Keyword(s):  
Glial Cell ◽  
Glial Cells ◽  
Synaptic Input ◽  
Medial Nucleus ◽  
Synaptic Structure ◽  
Excitatory Synaptic Input ◽  
Cell Processes ◽  
To Receive ◽  
Trapezoid Body ◽  
Axosomatic Synapse

Glial cell processes are part of the synaptic structure and sense spillover of transmitter, while some glial cells can even receive direct synaptic input. Here, we report that a defined type of glial cell in the medial nucleus of the trapezoid body (MNTB) receives excitatory glutamatergic synaptic input from the calyx of Held (CoH). This giant glutamatergic terminal forms an axosomatic synapse with a single principal neuron located in the MNTB. The NG2 glia, as postsynaptic principal neurons, establish synapse-like structures with the CoH terminal. In contrast to the principal neurons, which are known to receive excitatory as well as inhibitory inputs, the NG2 glia receive mostly, if not exclusively, α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid receptor–mediated evoked and spontaneous synaptic input. Simultaneous recordings from neurons and NG2 glia indicate that they partially receive synchronized spontaneous input. This shows that an NG2+ glial cell and a postsynaptic neuron share presynaptic terminals.

scholarly journals Low pH enhances connexin32 degradation in the pancreatic acinar cell

2014 ◽  
Vol 307 (1) ◽  
pp. G24-G32 ◽  
Author(s):  
Anamika M. Reed ◽  
Thomas Kolodecik ◽  
Sohail Z. Husain ◽  
Fred S. Gorelick
Keyword(s):  
Gap Junctions ◽  
Acinar Cell ◽  
Intercellular Communication ◽  
Pancreatic Acinar Cell ◽  
Low Ph ◽  
Extracellular Ph ◽  
Gap Junctional Intercellular Communication ◽  
Junction Protein ◽  
Clinical Conditions ◽  
Gap Junctional

Decreased extracellular pH is observed in a number of clinical conditions and can sensitize to the development and worsen the severity of acute pancreatitis. Because intercellular communication through gap junctions is pH-sensitive and modulates pancreatitis responses, we evaluated the effects of low pH on gap junctions in the rat pancreatic acinar cell. Decreasing extracellular pH from 7.4 to 7.0 significantly inhibited gap junctional intracellular communication. Acidic pH also significantly reduced levels of connexin32, the predominant gap junction protein in acinar cells, and altered its localization. Increased degradation through the proteasomal, lysosomal, and autophagic pathways mediated the decrease in connexin32 under low-pH conditions. These findings provide the first evidence that low extracellular pH can regulate gap junctional intercellular communication by enhancing connexin degradation.

Tetraethylammonium modifies gap junctions between pancreatic beta-cells

1981 ◽  
Vol 240 (3) ◽  
pp. C116-C120 ◽  
Author(s):  
M. S. Sheppard ◽  
P. Meda
Keyword(s):  
Beta Cell ◽  
Gap Junctions ◽  
Beta Cells ◽  
Insulin Release ◽  
Pancreatic Beta Cells ◽  
Freeze Fracture ◽  
Potassium Conductance ◽  
Median Number ◽  
Rat Islets Of Langerhans ◽  
Gap Junctional

Gap junctions between pancreatic beta-cells were quantitatively assessed in freeze-fracture replicas of isolated rat islets of Langerhans incubated for 90 min with or without the potassium conductance blocker tetraethylammonium (TEA). The results show that TEA increases the median number of particles per beta-cell gap junction but not the frequency of gap junctions at both nonstimulating and threshold-stimulating concentrations of glucose. TEA increased the relative gap junctional area at both concentrations of glucose. TEA had no effect on insulin release at a basal concentration of glucose but potentiated that release at the threshold glucose level. Thus TEA modifies beta-cell gap junctions independently of its effect on insulin release. However, the junctional changes observed were greater when insulin release was also elevated.

Phosphorylation of connexin43 gap junction protein in uninfected and Rous sarcoma virus-transformed mammalian fibroblasts

1990 ◽  
Vol 10 (4) ◽  
pp. 1754-1763
Author(s):  
D S Crow ◽  
E C Beyer ◽  
D L Paul ◽  
S S Kobe ◽  
A F Lau
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Rous Sarcoma Virus ◽  
Gap Junctional Communication ◽  
Rous Sarcoma ◽  
Junctional Communication ◽  
Junction Protein ◽  
Sarcoma Virus ◽  
Gap Junction Protein ◽  
Gap Junctional

Gap junctions are membrane channels that permit the interchange of ions and other low-molecular-weight molecules between adjacent cells. Rous sarcoma virus (RSV)-induced transformation is marked by an early and profound disruption of gap-junctional communication, suggesting that these membrane structures may serve as sites of pp60v-src action. We have begun an investigation of this possibility by identifying and characterizing putative proteins involved in junctional communication in fibroblasts, the major cell type currently used to study RSV-induced transformation. We found that uninfected mammalian fibroblasts do not appear to contain RNA or protein related to connexin32, the major rat liver gap junction protein. In contrast, vole and mouse fibroblasts contained a homologous 3.0-kilobase RNA similar in size to the heart tissue RNA encoding the gap junction protein, connexin43. Anti-connexin43 peptide antisera specifically reacted with three proteins of approximately 43, 45 and 47 kilodaltons (kDa) from communicating fibroblasts. Gap junctions of heart cells contained predominantly 45- and 47-kDa species similar to those found in fibroblasts. Uninfected fibroblast 45- and 47-kDa proteins were phosphorylated on serine residues. Phosphatase digestions of 45- and 47-kDa proteins and pulse-chase labeling studies indicated that these proteins represented phosphorylated forms of the 43-kDa protein. Phosphorylation of connexin protein appeared to occur shortly after synthesis, followed by an equally rapid dephosphorylation. In comparison with these results, connexin43 protein in RSV-transformed fibroblasts contained both phosphotyrosine and phosphoserine. Thus, the presence of phosphotyrosine in connexin43 correlates with the loss of gap-junctional communication observed in RSV-transformed fibroblasts.

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