Stages in the assembly of pleated and smooth septate junctions in developing insect embryos

1982 ◽  
Vol 56 (1) ◽  
pp. 245-262 ◽  
Author(s):  
N.J. Lane ◽  
L.S. Swales
Keyword(s):  
Embryonic Development ◽  
Freeze Fracture ◽  
Organizational Capacity ◽  
Intramembranous Particle ◽  
Septate Junctions ◽  
Thin Sections ◽  
Intramembranous Particles ◽  
Initial Event ◽  
Random Arrays ◽  
Insect Embryos

The stages that occur during the assembly of both pleated and smooth septate junctions in developing insect tissues have been examined. The oesophagus and mid-gut of the embryonic moth, and the oesophagus and central nervous system (CNS) of the locust embryo, have been investigated in thin sections and by freeze-fracture during the course of membrane biogenesis. The smooth septate junctions developing between the lateral borders of the mid-gut exhibit, in the early stages, individual intramembranous particles becoming aligned into short ridges. These ultimately migrate over the membrane face and fuse into longer arrays, which become stacked in parallel with other ridges to form the characteristic mature form of the junction just before hatching. Pleated septate junctions occur between the cells both of the oesophagus and of the perineurium, which ensheathes the neurones and the neuroglial cells in the locust CNS; these are also fully formed by the end of embryonic development. The pleated junctions appear to be assembled during the later stages of CNS or gut differentiation, arising first in embryos about two-thirds of the way through development. During their maturation, the initial event seems to be a membrane depression in the P face, which occurs in patches over the presumptive junctional membrane. Into these depressed regions or ‘formation-plaque’ areas, 8–10 nm particles appear to be inserted intramembranously in apparently random arrays. These particles are the most common elements but larger particles are also present; the former ultimately become aligned in a row. With time, other intramembranous particles come to lie in rows parallel to the original one. By hatching, the typical undulating stacks of parallel intramembranous particle rows are fully formed. Gap junctions also form between the same perineurial or oesophageal cells, usually before, but in some cases at the same time, or just after, the septate junctions have been assembled. Tricellular associations between cells also appear around the same time in embryonic development. The simultaneous assembly of these different junctions reflects a high degree of organizational capacity at the membrane level.

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 Septate junctions in imaginal disks of Drosophila: a model for the redistribution of septa during cell rearrangement.

1982 ◽  
Vol 94 (1) ◽  
pp. 77-87 ◽  
Author(s):  
D K Fristrom
Keyword(s):  
Freeze Fracture ◽  
Septate Junction ◽  
Lateral Boundary ◽  
Progressive Change ◽  
Septate Junctions ◽  
Thin Sections ◽  
Cell Rearrangement ◽  
Imaginal Disks ◽  
Discrete Domains ◽  
Small Channels

The organization of septate junctions during morphogenesis of imaginal disks is described from freeze-fracture replicas and thin sections with a view to understanding junction modulation during rearrangements of cells in epithelia. The septate junctions of each epithelial cell of the disk are distributed in a number of discrete domains equal to the number of neighboring cells. Individual septa traverse domains of contact between pairs of adjacent cells, turn downwards at the lateral boundary of the domain and run parallel to the intersection with a third cell. This arrangement leaves small channels at three-cell intersections that are occupied by specialized structures termed "tricellular plugs." Cell rearrangement involves a progressive change in the width of contact domains between adjacent cells, until old contacts are broken and new ones established. It is proposed that the septate junction adjusts to the changing width of domains by the compaction or extension of existing septa. This redistribution of septa theoretically allows a transepithelial barrier to be maintained during cell rearrangements. The applicability of this model to other epithelial tissues is discussed.

scholarly journals Ultrastructure of the sodium pump: Comparison of thin sectioning, negative staining, and freeze-fracture of purified, membrane-bound (Na+, K+)-ATPase

1977 ◽  
Vol 75 (3) ◽  
pp. 619-634 ◽  
Author(s):  
N Deguchi ◽  
PL Jorgensen ◽  
AB Maunsbach
Keyword(s):  
Membrane Surface ◽  
Freeze Fracture ◽  
Negative Staining ◽  
Intramembranous Particle ◽  
Freeze Fracturing ◽  
Intramembranous Particles ◽  
Membrane Surfaces ◽  
Thin Sectioning ◽  
Surface Particle ◽  
Protein Components

Purified (Na+, K+)-ATPase was studied by electron microscopy after thin sectioning, negative staining, and freeze-fracturing, particular emphasis being paid to the dimensions and frequencies of substructures in the membranes. Ultrathin sections show exclusively flat or cup-shaped membrane fragments which are triple-layered along much of their length and have diameters of 0.1-0.6 μm. Negative staining revealed a distinct substructure of particles with diameters between 30 and 50 A and with a frequency of 12,500 +/- 2,400 (SD) per μm(2). Comparisons with sizes of the protein components suggest that each surface particle contains as its major component one large catalytic chain with mol wt close to 100,000 and that two surface particles unite to form the unit of (Na+,K+)-ATPase which binds one molecule of ATP or ouabain. The further observations that the surface particles protrude from the membrane surface and are observed on both membrane surfaces in different patterns and degrees of clustering suggest that protein units span the membrane and are capable of lateral mobility. Freeze-fracturing shows intramembranous particles with diameters of 90-110 A and distributed on both concave and convex fracture faces with a frequency of 3,410 +/- 370 per μm(2) and 390 +/- 170 per μm(2), respectively. The larger diameters and three to fourfold smaller frequency of the intramembranous particles as compared to the surface particles seen after negative staining may reflect technical differences between methods, but it is more likely that the intramembranous particle is an oliogomer composed of two or even more of the protein units which form the surface particles.

scholarly journals Development of cell junctions in sea-urchin embryos

1983 ◽  
Vol 62 (1) ◽  
pp. 27-48
Author(s):  
E. Spiegel ◽  
L. Howard
Keyword(s):  
Epithelial Cells ◽  
Basement Membrane ◽  
Digestive Tract ◽  
Sea Urchin ◽  
Freeze Fracture ◽  
Cell Junctions ◽  
Septate Junctions ◽  
Thin Sections ◽  
Sea Urchin Embryos ◽  
Lanthanum Tracer

The development of cell junctions in sea-urchin embryos has been investigated using thin sections, lanthanum-tracer and freeze-fracture techniques. Three types of desmosomes are present: belt desmosomes and spot desmosomes, which attach cells to each other, and hemi-desmosomes, which attach cells to the basement membrane. Two types of septate junctions are present: the straight, unbranched, double-septum septate, which is present in epithelial cells throughout embryogenesis, and the pleated, anastomosing, single-septum septate. The latter is formed only on cells that have invaginated to the interior of the embryo to form the digestive tract. The pleated junctions are shown to replace the straight junctions that were originally present before the cells migrated to the interior. It is suggested that these pleated septates may be specialized for digestive processes, since they are developed just prior to feeding and are retained in the adult intestine. Tricellular junctions, which join the bicellular junctions of three adjoining cells, have been identified in the embryo and in the adult intestine. Evidence for the presence of gap junctions was not obtained, but there are indications of their presence.

scholarly journals A freeze-fracture and lanthanum tracer study of the complex junction between Sertoli cells of the canine testis.

1978 ◽  
Vol 76 (1) ◽  
pp. 57-75 ◽  
Author(s):  
C J Connell
Keyword(s):  
Tight Junctions ◽  
Sertoli Cells ◽  
Freeze Fracture ◽  
Intercellular Junctions ◽  
Septate Junction ◽  
Septate Junctions ◽  
Thin Sections ◽  
En Face ◽  
Lanthanum Tracer ◽  
Complex Junction

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.

scholarly journals CRYOPROTECTANT-INDUCED REDISTRIBUTION OF INTRAMEMBRANOUS PARTICLES IN MOUSE LYMPHOCYTES

1974 ◽  
Vol 60 (1) ◽  
pp. 192-203 ◽  
Author(s):  
John A. McIntyre ◽  
Norton B. Gilula ◽  
Morris J. Karnovsky
Keyword(s):  
B Cells ◽  
Freeze Fracture ◽  
Cell Types ◽  
Lymphoid Cells ◽  
T And B Cells ◽  
Thin Sections ◽  
Intramembranous Particles ◽  
Glycerol Treatment ◽  
Mouse Lymphocytes ◽  
Aggregation Phenomenon

This study demonstrates, by freeze fracture, clustering of intramembranous particles caused by cryoprotectant treatment of intact unfixed mouse lymphoid cells. Both T and B cells react in a similar fashion, while similar clustering of particles is not observed in some other cell types. The intramembranous particles can be aggregated by incubating unfixed cells in glycerol or dimethylsulfoxide (DMSO) before freezing. The aggregation phenomenon is dependent on the length of time of exposure and the concentration of the cryoprotectants. Further, the cells remain viable and the cryoprotectant-induced clustering is completely reversible. Prefixation of glycerol-treated cells with glutaraldehyde prevents the formation of these particle clusters, and unfixed nonglycerinated cells show no clusters. Thin sections of cells exposed to glycerol or DMSO without previous fixation exhibit bizarre membrane alterations and numerous other degenerative changes. These observations stress the importance of prefixation of lymphoid cells before exposure to glycerol or DMSO, as well as indicate that the membrane characteristics of certain cell types may be probed by glycerol treatment of unfixed cells.

Intercellular junctions in the larval epidermis of the colonial ascidian Distaplia occidentalis: a thin-section and freeze-fracture examination

1986 ◽  
Vol 64 (1) ◽  
pp. 112-117 ◽  
Author(s):  
Michael J. Cavey ◽  
Richard L. Wood
Keyword(s):  
Electron Microscopy ◽  
Freeze Fracture ◽  
Intercellular Junctions ◽  
Epidermal Cells ◽  
Cellular Membranes ◽  
Colonial Ascidian ◽  
Thin Sections ◽  
Intramembranous Particles ◽  
Transmission Electron ◽  
Columnar Cells

The larval epidermis of the colonial ascidian Distaplia occidentalis is a unilayered epithelium consisting of squamous and cuboidal or low columnar cells. The epidermal cells are laterally folded and interdigitated or overlapped. The occluding (tight) junctions and the close (gap) junctions that join the epidermal cells have been examined by transmission electron microscopy. In thin sections, the occluding junction is represented by focal fusions of the apposed plasmalemmata. Freeze-fracture replicas of the occluding junction show linear, anastomosing arrays of intramembranous particles on the protoplasmic faces of the cellular membranes. In thin sections of the close junction, the apposed plasmalemmata are mutually parallel and separated by a narrow intercellular cleft. Freeze-fracture replicas of the close junction reveal macular aggregations of intramembranous particles on the protoplasmic faces of the cellular membranes.

Gap junctions in the prothoracic glands of the tobacco hornworm, Manduca sexta

1992 ◽  
Vol 50 (1) ◽  
pp. 706-707
Author(s):  
Ji-da Dai ◽  
M. Joseph Costello ◽  
Lawrence I. Gilbert
Keyword(s):  
Gap Junctions ◽  
Small Molecules ◽  
Manduca Sexta ◽  
Freeze Fracture ◽  
Cell Communication ◽  
Cellular Level ◽  
Thin Sections ◽  
Prothoracic Glands ◽  
Polyhydroxylated Steroids ◽  
Stimulation Of

Insect molting and metamorphosis are elicited by a class of polyhydroxylated steroids, ecdysteroids, that originate in the prothoracic glands (PGs). Prothoracicotropic hormone stimulation of steroidogenesis by the PGs at the cellular level involves both calcium and cAMP. Cell-to-cell communication mediated by gap junctions may play a key role in regulating signal transduction by controlling the transmission of small molecules and ions between adjacent cells. This is the first report of gap junctions in the PGs, the evidence obtained by means of SEM, thin sections and freeze-fracture replicas.

Membranes in lupin root nodules. II. Preparation and properties of peribacteroid membranes and bacteroid envelope inner membranes from developing lupin nodules

1978 ◽  
Vol 30 (1) ◽  
pp. 151-174
Author(s):  
J.G. Robertson ◽  
M.P. Warburton ◽  
P. Lyttleton ◽  
A.M. Fordyce ◽  
S. Bullivant
Keyword(s):  
Sucrose Gradient ◽  
Phosphotungstic Acid ◽  
Nadh Oxidase ◽  
Osmotic Shock ◽  
Root Nodules ◽  
Freeze Fracture ◽  
Electrophoretic Analysis ◽  
Thin Sections ◽  
Peribacteroid Space ◽  
Gradient Fractionation

Peribacteroid membranes and bacteroid envelope inner membranes have been isolated from developing lupin nodules. Isolation of the peribacteroid membranes was achieved by first preparing membrane-enclosed bacteroids free from other plant organelles or membranes. The peribacteroid membranes were then released by osmotic shock and purified by centrifugation to equilibrium on sucrose gradients. The bacteroids were broken in a pressure cell and the bacteroid envelope inner membranes were isolated using sucrose gradient fractionation of the bacteroid total envelope preparation. The density of the peribacteroid membranes decreased during the period of development of N2-fixation in lupin nodules from 1.148 g/ml for nodules from 12-day plants to 1.137 g/ml for nodules from 18-day plants. The density of the bacteroid envelope inner membranes from nodules from 18-day plants was 1–153 g/ml. The identity and homogeneity of the isolated membranes was established, by comparison with membranes in intact nodules, using phosphotungstic acid and silver staining of thin sections and particle densitites on faces of freeze-fracture replicas of the membranes. Analyses for NADH oxidase and succinate dehydrogenase, spectral analyses and gel-electrophoretic analysis of proteins were also used to characterize the membrane and soluble protein fractions from the nodules. The ratio of lipid to protein was 6.1 for the peribacteroid membranes and 2.5 for the bacteroid envelope inner membranes. Leghaemoglobin was localized in the plant cytoplasm in lupin nodules and not in the peribacteroid space.

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.

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