scholarly journals Tight-junctional strands first appear in regions where three cells meet in differentiating olfactory epithelium: a freeze-fracture study

1988 ◽  
Vol 89 (4) ◽  
pp. 495-505
Author(s):  
B.P. Menco
Keyword(s):  
Embryonic Development ◽  
Gap Junction ◽  
Tight Junctions ◽  
Olfactory Epithelium ◽  
Freeze Fracture ◽  
Subsequent Development ◽  
Epithelial Surface ◽  
Direction Parallel ◽  
Longitudinal Orientation ◽  
Fracture Study

Tight junctions of the olfactory epithelium of rat embryos were studied at the 14th day of gestation and during their subsequent development. Two different epithelial morphologies could be distinguished at the 14th gestational day. In one group of embryos the epithelial surface appeared undifferentiated, with tight-junctional strands found exclusively in regions where three cells met. The main orientation of these strands is in a direction parallel to the longitudinal orientation of the epithelial cells. These junctions resemble tight junctions that interconnect three cells, i.e. tricellular tight junctions, in that respect. However, unlike these the junctions mainly have single strands of particles, whereas tricellular junctions usually consist of paired strands of particles. Tight-junctional strands were completely absent in areas where two cells met. These areas, i.e. those of incipient bicellular tight junctions, had gap-junction-like aggregates of intramembranous particles. Another group of 14-day-old embryos displayed a differentiating olfactory epithelial surface with bicellular as well as tricellular tight-junctional strands. The latter ones were paired. Here too the tight-junctional belts displayed some gap-junction-like aggregates of particles, but there were considerably fewer of these than earlier. As one or the other tight-junctional appearance was always seen in a single freeze-fracture replica, it is reasonable to assume that the two tight-junctional appearances reflect a sequential pattern of differentiation peculiar to the whole surface of the olfactory epithelium, i.e. to surfaces of receptor cells as well as to surfaces of supporting cells. It would appear that, at the onset of olfactory epithelial differentiation, tight junctions first interconnect cells in regions where three cells meet and that tricellular strand formation precedes the formation of bicellular strands. When strands were present at the 14th day of embryonic development, their numbers were lower than those found later. However, strand packing, expressed as the density per micrometre of strands parallel to the epithelial surface, increased beginning at the 16th day of embryonic development.

scholarly journals A freeze-fracture study on the developing satellite cells of spinal ganglia in the chick embryo

1988 ◽  
Vol 46 (1) ◽  
pp. 6-9
Author(s):  
Claudio A. Ferraz de Carvalho ◽  
Ciro F. da Silva
Keyword(s):  
Chick Embryo ◽  
Gap Junctions ◽  
Tight Junctions ◽  
Small Groups ◽  
Satellite Cells ◽  
Freeze Fracture ◽  
Fracture Analysis ◽  
Spinal Ganglia ◽  
Pinocytotic Vesicles ◽  
Fracture Study

A freeze-fracture analysis of the satellite cells of spinal ganglia of the chick embryo was performed in 8 successive stages of development, from the 5th incubation day to hatching. The characteristic laminar disposition of the cells were first observed on the 7th day. Tight junctions were found at the 20th incubation day. Small groups or irregular aggregates of particles, but not gap junctions, were described on the 7th and 8th days. Pinocytotic vesicles were pointed out in the different stages considered.

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.

Tight junctions of human keratinocytes in primary culture: A freeze-fracture study

1983 ◽  
Vol 82 (3) ◽  
pp. 309-313 ◽  
Author(s):  
Yasuo Kitajima ◽  
Kiyomi Eguchi ◽  
Tadao Ohno ◽  
Shunji Mori ◽  
Hideo Yaoita
Keyword(s):  
Primary Culture ◽  
Tight Junctions ◽  
Freeze Fracture ◽  
Human Keratinocytes ◽  
Fracture Study

scholarly journals Tight junctions in the choroid plexus epithelium. A freeze-fracture study including complementary replicas.

1979 ◽  
Vol 80 (3) ◽  
pp. 662-673 ◽  
Author(s):  
B van Deurs ◽  
J K Koehler
Keyword(s):  
Choroid Plexus ◽  
Tight Junctions ◽  
Freeze Fracture ◽  
Choroid Plexus Epithelium ◽  
Sprague Dawley ◽  
Fixed Tissue ◽  
Average Width ◽  
Mean Values ◽  
Sprague Dawley Rats ◽  
Fracture Study

The tight junctions of the choroid plexus epithelium of rats were studied by freeze-fracture. In glutaraldehyde-fixed material, the junctions exhibited rows of aligned particles and short bars on P-faces, the E-faces showing grooves bearing relatively many particles. A particulate nature of the junctional strands could be established by using unfixed material. The mean values of junctional strands from the lateral, third, and fourth ventricles of Lewis rats were 7.5 +/- 2.6, 7.4 +/- 2.2, and 7.5 +/- 2.4; and of Sprague-Dawley rats 7.7 +/- 3.4, 7.4 +/- 2.3, and 7.3 +/- 1.6. Examination of complementary replicas (of fixed tissue) showed that discomtinuities are present in the junctional strands: 42.2 +/- 4.6% of the length of measured P-face ridges were discontinuities, and the total amount of complementary particles in E-face grooves constituted 17.8 +/- 4.4% of the total length of the grooves, thus approximately 25% of the junctional strands can be considered to be discontinuous. The average width of the discontinuities, when corrected for complementary particles in E-face grooves, was 7.7 +/- 4.5 nm. In control experiments with a "tighter" tight junction (small intestine), complementary replicas revealed that the junctional fibrils are rather continuous and that the very few particles in E-face grooves mostly filled out discontinuities in the P-face ridges. Approximately 5% of the strands were found to be discontinuous. These data support the notion that the presence of pores in the junctional strands of the choroid plexus epithelium may explain the high transepithelial conductance in a "leaky" epithelium having a high number of junctional strands. However, loss of junctional material during fracturing is also considered as an alternative explanation of the present results.

A freeze-fracture study of tight junction structure in sheep mammary gland epithelium during pregnancy and lactation

1982 ◽  
Vol 49 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Geoffrey Morgan ◽  
F. B. Peter Wooding
Keyword(s):  
Mammary Gland ◽  
Tight Junction ◽  
Tight Junctions ◽  
Lateral Surface ◽  
Freeze Fracture ◽  
Mammary Epithelium ◽  
Secretory Cells ◽  
Pregnancy And Lactation ◽  
Fracture Study ◽  
Junction Structure

SUMMARYFreeze fractures of the tight junctions at the apices of sheep mammary secretory cells showed that the junction at 72 d of pregnancy was significantly wider than at any later stage. The number of ridges in the junction only increased significantly between 122 and 142 d of pregnancy. The initially even distribution of intramembrane particles across the tight junction changed gradually until in the fully lactating animal there were far more particles on the lateral surface of the plasmalemma. Possible correlations between these changes, the alterations in permeability of the mammary epithelium, and the differences in hormone levels are briefly discussed.

scholarly journals Structural and Functional Regulation of Tight Junctions by RhoA and Rac1 Small GTPases

1998 ◽  
Vol 142 (1) ◽  
pp. 101-115 ◽  
Author(s):  
Tzuu-Shuh Jou ◽  
Eveline E. Schneeberger ◽  
W. James Nelson
Keyword(s):  
Tight Junctions ◽  
Spatial Organization ◽  
Mdck Cells ◽  
Protein Localization ◽  
Freeze Fracture ◽  
Tracer Diffusion ◽  
Small Gtpases ◽  
Dominant Negative ◽  
Solute Diffusion ◽  
Fence Function

Tight junctions (TJ) govern ion and solute diffusion through the paracellular space (gate function), and restrict mixing of membrane proteins and lipids between membrane domains (fence function) of polarized epithelial cells. We examined roles of the RhoA and Rac1 GTPases in regulating TJ structure and function in MDCK cells using the tetracycline repressible transactivator to regulate RhoAV14, RhoAN19, Rac1V12, and Rac1N17 expression. Both constitutively active and dominant negative RhoA or Rac1 perturbed TJ gate function (transepithelial electrical resistance, tracer diffusion) in a dose-dependent and reversible manner. Freeze-fracture EM and immunofluoresence microscopy revealed abnormal TJ strand morphology and protein (occludin, ZO-1) localization in RhoAV14 and Rac1V12 cells. However, TJ strand morphology and protein localization appeared normal in RhoAN19 and Rac1N17 cells. All mutant GTPases disrupted the fence function of the TJ (interdomain diffusion of a fluorescent lipid), but targeting and organization of a membrane protein in the apical membrane were unaffected. Expression levels and protein complexes of occludin and ZO-1 appeared normal in all mutant cells, although ZO-1 was more readily solubilized from RhoAV14-expressing cells with Triton X-100. These results show that RhoA and Rac1 regulate gate and fence functions of the TJ, and play a role in the spatial organization of TJ proteins at the apex of the lateral membrane.

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