The ultrastructure of a haemogregarine parasitic in Gehyra variegata (Duméril & Bibron, 1836)

Parasitology ◽  
1967 ◽  
Vol 57 (2) ◽  
pp. 251-261 ◽  
Author(s):  
W. E. Stehbens ◽  
M. R. L. Johnston
Keyword(s):  
Endoplasmic Reticulum ◽  
Technical Assistance ◽  
Red Cell ◽  
Unit Membrane ◽  
Cell Cytoplasm ◽  
Erythrocytic Stage ◽  
Membranous Structure ◽  
Conventional Unit ◽  
Gehyra Variegata

The ultrastructure of the intra-erythrocytic stage of a haemogregarine in the gecko, Gehyra variegata, has been studied and numerous points of similarity to Plasmodium, Toxoplasma, Sarcocystis, Lankesterella, Eimeria and the M-organism were found. The protozoon was invested by a triple-layered pellicle, and possessed at least two micropyles. A conoid and apical rings were observed at the anterior end. Other cell constituents included nucleus, microtubules, endoplasmic reticulum, mitochondria, toxonemes and a variety of vacuoles. Loosely surrounding the parasite was an unusual convoluted membrane, which in appropriate planes of section, displayed corrugations on both surfaces. It was not clear whether this membranous structure should be regarded as an integral part of the protozoon or as an external coat which could be discarded upon emergence from the host red cell. Within its external sheath, the parasite lay in a periparasitic vacuole which was limited by a conventional unit membrane from the host red cell cytoplasm. The parasite did not exhibit any evidence of pinocytosis or phagocytosis.Our sincere thanks are due to Dr E. H. Mercer, Professor J. D. Smyth and Dr M. J. Mackerras for advice. Miss N. Carroll gave technical assistance.

scholarly journals FINE STRUCTURE OF THE ASEXUAL STAGES OF PLASMODIUM ELONGATUM

1967 ◽  
Vol 34 (1) ◽  
pp. 229-249 ◽  
Author(s):  
Masamichi Aikawa ◽  
Clay G. Huff ◽  
Helmuth Sprinz
Keyword(s):  
Fine Structure ◽  
Host Cell ◽  
Malarial Parasite ◽  
Red Cell ◽  
Digestive Vacuole ◽  
Cell Cytoplasm ◽  
Erythrocytic Stage ◽  
New Host ◽  
Feeding Mechanism ◽  
Host Cell Cytoplasm

Plasmodium elongatum, an avian malarial parasite, differs from other such parasites by infecting both the circulating red blood cells and the hematopoietic cells. The exoerythrocytic development of P. elongatum occurs mainly in these red cell precursors. The fine structure of the asexual stages of P. elongatum has been studied in the bone marrow and peripheral blood of canaries and compared with that of the asexual stages of other avian malarial parasites. With minor differences, the merozoites of P. elongatum possess the same organelles as those in the exoerythrocytic merozoites of P. fallax and the erythrocytic stages of P. cathemerium, P. lophurae, P. fallax, and P. gallinaceum. The developmental sequence is also essentially similar to that of other avian malarial parasites, in that upon entry into a new host cell, the dedifferentiation, growth, and redifferentiation phases take place. However, we have found some important differences in the feeding mechanism of P. elongatum. The cytostome is involved in the ingestion of host cell cytoplasm in both exoerythrocytic and erythrocytic stages, in contrast to P. fallax, in which the cytostome is inactive in the exoerythrocytic stages. In P. elongatum, host cell cytoplasm is ingested through the cytostome, and "boluses" are formed and incorporated into a large digestive vacuole. Subsequently, the digestion of the boluses takes place in this digestive vacuole. Thus, in regard to the function of the cytostome, the exoerythrocytic stages of P. elongatum appear to be closely related to the erythrocytic stage which has a feeding mechanism similar to that of the erythrocytic stage of other avian malarial parasites.

scholarly journals Ultrastructural Changes in the Pancreata of Selenium-Vitamin E-Deficient Chicks

1977 ◽  
Vol 14 (6) ◽  
pp. 629-642 ◽  
Author(s):  
A. H. Rebar ◽  
J. F. Van Vleet
Keyword(s):  
Endoplasmic Reticulum ◽  
Vitamin E ◽  
Acinar Cell ◽  
Interstitial Fibrosis ◽  
Ultrastructural Changes ◽  
Zymogen Granules ◽  
Cell Cytoplasm ◽  
Torula Yeast ◽  
Cell Changes ◽  
Ductular Proliferation

Three hundred and seventy 1-day-old male, white Leghorn chicks were divided into seven groups and fed a series of semipurified torula yeast diets either deficient in or supplemented with selenium and vitamin E. Chicks in each group were necropsied sequentially and the pancreata examined by light microscopy. Selected pancreata of selenium deficient chicks in various stages of the deficiency disease were examined by electron microscopy. Supplements of either selenium (0.2 mg/kg) or vitamin E (100 IU/kg diet) resulted in protection against pancreatic lesions. Changes in pancreata of selenium deficient chicks progressed from cytoplasmic vacuolation of acinar cell cytoplasm to focal disseminated acinar necrosis. There was ductular proliferation and interstitial fibrosis in advanced lesions. Acini around islets were less frequently affected than acini further away. Ultrastructurally, the mildest lesions were focal dilation of the endoplasmic reticulum and autophagic vacuoles in acinar cell cytoplasm. Necrotic areas contained both membranous and granular debris and fragments of intact endoplasmic reticulum. In fibrotic pancreata the main acinar cell changes were uniform dilation of endoplasmic reticulum and reduction in number of zymogen granules.

Acetylcholinesterase in Human Erythroid Cells

1973 ◽  
Vol 12 (3) ◽  
pp. 911-923
Author(s):  
R. J. SKAER
Keyword(s):  
Endoplasmic Reticulum ◽  
Nervous System ◽  
Golgi Apparatus ◽  
Red Cells ◽  
The Other ◽  
Red Cell ◽  
Erythroid Cells ◽  
Cell Replacement ◽  
Kinetics Of ◽  
Human Red Cells

Acetylcholinesterase is present in human red cells but cannot be demonstrated by the copper thiocholine test. The enzyme is revealed, however, in the perinuclear cisterna, endoplasmic reticulum and Golgi apparatus of red cell precursors. It is suggested that 2 forms of the enzyme are present, one of which can be demonstrated by the copper thiocholine test, the other cannot; one form may be the precursor of the other. These observations may cast light on the kinetics of red cell replacement and on the interpretation of the results from the copper thiocholine test on other tissues such as the nervous system.

The Fine Structure of the Eye of the Leech, Helobdella Stagnalis

1967 ◽  
Vol 2 (3) ◽  
pp. 341-348
Author(s):  
A. W. CLARK
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Complex ◽  
Photoreceptor Cell ◽  
Receptor Cell ◽  
Pigment Cell ◽  
Cell Mass ◽  
Pigment Cells ◽  
Cell Cytoplasm ◽  
Receptor Cells ◽  
Intracellular Vesicle

The eye of the rhynchobdellid leech, Helobdella stagnalis, has been examined with the electron microscope. The eye is composed of a cup of pigment cells surrounding a compact mass of photo-receptor cells. In addition to pigment granules, the pigment-cell cytoplasm is characterized by mitochondria, a Golgi complex, and profiles of rough-surfaced endoplasmic reticulum. The photoreceptor cell contains a microvillous rhabdomere. The microvilli arise from the membrane of a large intracellular vesicle and obliterate much of its lumen. No connexion between the lumen of the intracellular vesicle and the extracellular space has been observed. The plasmalemma of the photoreceptor cell is folded to form thin pleats of cytoplasm which separate adjacent receptor cells from each other. No glial-like cells have been seen in the receptor cell mass. Directly subjacent to the microvilli and surrounding the intracellular vesicle is a tortuous and predominantly smooth-surfaced endoplasmic reticulum. A pair of centrioles is found near the rhabdomere. The cytoplasm around the nucleus is characterized by smooth- and rough-surfaced elements of endoplasmic reticulum, many mitochondria, and a Golgi complex. Proximally, the receptor cell narrows to form a nerve fibre which joins those from other cells to form the optic nerve.

Elektronenmikroskopische Untersuchungen über die Eizellbildung und Eizellreifung des Lebermooses Sphaerocarpus donnellii Aust.

1965 ◽  
Vol 20 (8) ◽  
pp. 795-801 ◽  
Author(s):  
Lothar Diers
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Phase Contrast ◽  
Lipid Droplets ◽  
Unit Membrane ◽  
Light Phase ◽  
Lamellar System ◽  
Small Bodies ◽  
Canal Cell ◽  
Ventral Canal

The formation and maturation of the egg of the liverwort, Sphaerocarpus donnellii, was investigated by light, phase contrast and particularly by electron microscopy. The division of the central cell into the egg and the ventral canal cell, and the maturation of the egg, is completed within four days. All stages of this formation and maturation were examined under the electron microscope after fixation in KMnO4 or OsO4. — In the maturing egg there always occur the endoplasmic reticulum, well recognisable plastids with a poorly developed lamellar system, numerous mitochondria and dictyosomes, a rising number of lipid droplets, unknown small bodies limited by a unit membrane, and numerous ribosomes. During maturation the nucleus considerably enlarges and forms evaginations into the cytoplasm. Starch is increasingly deposited in the plastids. A degeneration of plastids has not been found.

scholarly journals Autophagy requires endoplasmic reticulum targeting of the PI3-kinase complex via Atg14L

2010 ◽  
Vol 190 (4) ◽  
pp. 511-521 ◽  
Author(s):  
Kohichi Matsunaga ◽  
Eiji Morita ◽  
Tatsuya Saitoh ◽  
Shizuo Akira ◽  
Nicholas T. Ktistakis ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
Embryonic Stem ◽  
Pi3 Kinase ◽  
Class Iii ◽  
Autophagosome Formation ◽  
Membranous Structure ◽  
Er Targeting ◽  
Endoplasmic Reticulum Targeting ◽  
Phosphatidylinositol 3

Autophagy is a catabolic process that allows cells to digest their cytoplasmic constituents via autophagosome formation and lysosomal degradation. Recently, an autophagy-specific phosphatidylinositol 3-kinase (PI3-kinase) complex, consisting of hVps34, hVps15, Beclin-1, and Atg14L, has been identified in mammalian cells. Atg14L is specific to this autophagy complex and localizes to the endoplasmic reticulum (ER). Knockdown of Atg14L leads to the disappearance of the DFCP1-positive omegasome, which is a membranous structure closely associated with both the autophagosome and the ER. A point mutation in Atg14L resulting in defective ER localization was also defective in the induction of autophagy. The addition of the ER-targeting motif of DFCP1 to this mutant fully complemented the autophagic defect in Atg14L knockout embryonic stem cells. Thus, Atg14L recruits a subset of class III PI3-kinase to the ER, where otherwise phosphatidylinositol 3-phosphate (PI3P) is essentially absent. The Atg14L-dependent appearance of PI3P in the ER makes this organelle the platform for autophagosome formation.

Electron-microscope studies of Fasciola hepatica III. Further observations on the tegument and associated structures

Parasitology ◽  
1967 ◽  
Vol 57 (4) ◽  
pp. 633-637 ◽  
Author(s):  
L. T. Threadgold
Keyword(s):  
Endoplasmic Reticulum ◽  
Electron Microscope ◽  
Golgi Complex ◽  
Technical Assistance ◽  
Fasciola Hepatica ◽  
Glutaraldehyde Fixation ◽  
Research Associate ◽  
New Findings

Additional ultrastructural features of the tegument of Fasciola hepatica, after glutaraldehyde fixation and high resolution, have been observed.Two distinct types of tegumental cells are shown to be present, the type 1 cell having been previously described. Details of the fine structure of the nucleus, mitochondria, endoplasmic reticulum and Golgi complex of the type 2 cell are given. The type 2 cell is characterized by biconcave secretory bodies derived from the Golgi complex and the latter is intimately related to the granular endoplasmic reticulum, from which it is derived by blebbing. The type 2 cells are connected by protoplasmic tubes to the same surface syncytium as type 1 cells.These new findings of the structure of the tegument of Fasciola are compared with previous reports on the ultrastructure of the tegument in other flukes.I should like to express my sincere thanks to the following: the Wellcome Trust and S.R.C. for grants to purchase an Akashi TRS 50 and an A.E.I. E.M. 6B electron microscope respectively; the Royal Society for a personal grant to purchase a Reichert Ultramicrotome and a vacuum coating unit.My thanks are also due to Mr W. Ferguson for photographic skill and to Mr A. Lyness for technical assistance and microscope maintenance, and my Research Associate, Mrs S. S. E. Dermott, for expert electron-microscopy.

scholarly journals ON THE THICKNESS OF THE UNIT MEMBRANE

1963 ◽  
Vol 17 (2) ◽  
pp. 413-421 ◽  
Author(s):  
Toshiyuki Yamamoto
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Electron Micrographs ◽  
Synaptic Vesicles ◽  
Multivesicular Bodies ◽  
Unit Membrane ◽  
Cell Organelles ◽  
Membrane Unit ◽  
Nuclear Membranes ◽  
Golgi Vesicles

Peak-to-peak distances between two dense lines of the unit membranes of cell organelles were measured on electron micrographs. These distances were compared with corresponding measurements on the plasma membrane and assigned a percentage value. The comparison between organelle and plasma membrane was always carried out with the same negative, in order to exclude as far as possible errors due to differences in focus or other causes. It was revealed by this study that the membranous structures of the cell can be classified into two groups, one thicker and one thinner. Unit membranes of the thicker group (synaptic vesicles, vesicles and capsules of multivesicular bodies, Golgi vesicles) were not significantly different in thickness from the plasma membrane. Unit membranes of the thinner group (mitochondria, nuclear membranes, Golgi lamellae, endoplasmic reticulum), however, were between 85 and 90 per cent of the thickness of the plasma membrane.

scholarly journals Human Antiviral Protein MxA Forms Novel Metastable Membraneless Cytoplasmic Condensates Exhibiting Rapid Reversible Tonicity-Driven Phase Transitions

2019 ◽  
Vol 93 (22) ◽  
Author(s):  
Deodate Davis ◽  
Huijuan Yuan ◽  
Feng-Xia Liang ◽  
Yang-Ming Yang ◽  
Jenna Westley ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Apparatus ◽  
Viral Infection ◽  
Protein A ◽  
Cell Cytoplasm ◽  
Intact Cells ◽  
N Protein ◽  
P Bodies ◽  
Huh7 Cells ◽  
Resistance Protein

ABSTRACT Phase-separated biomolecular condensates of proteins and nucleic acids form functional membrane-less organelles (e.g., stress granules and P-bodies) in the mammalian cell cytoplasm and nucleus. In contrast to the long-standing belief that interferon (IFN)-inducible human myxovirus resistance protein A (MxA) associated with the endoplasmic reticulum (ER) and Golgi apparatus, we report that MxA formed membraneless metastable (shape-changing) condensates in the cytoplasm. In our studies, we used the same cell lines and methods as those used by previous investigators but concluded that wild-type MxA formed variably sized spherical or irregular bodies, filaments, and even a reticulum distinct from that of ER/Golgi membranes. Moreover, in Huh7 cells, MxA structures associated with a novel cytoplasmic reticular meshwork of intermediate filaments. In live-cell assays, 1,6-hexanediol treatment led to rapid disassembly of green fluorescent protein (GFP)-MxA structures; FRAP revealed a relative stiffness with a mobile fraction of 0.24 ± 0.02 within condensates, consistent with a higher-order MxA network structure. Remarkably, in intact cells, GFP-MxA condensates reversibly disassembled/reassembled within minutes of sequential decrease/increase, respectively, in tonicity of extracellular medium, even in low-salt buffers adjusted only with sucrose. Condensates formed from IFN-α-induced endogenous MxA also displayed tonicity-driven disassembly/reassembly. In vesicular stomatitis virus (VSV)-infected Huh7 cells, the nucleocapsid (N) protein, which participates in forming phase-separated viral structures, associated with spherical GFP-MxA condensates in cells showing an antiviral effect. These observations prompt comparisons with the extensive literature on interactions between viruses and stress granules/P-bodies. Overall, the new data correct a long-standing misinterpretation in the MxA literature and provide evidence for membraneless MxA biomolecular condensates in the uninfected cell cytoplasm. IMPORTANCE There is a long-standing belief that interferon (IFN)-inducible human myxovirus resistance protein A (MxA), which displays antiviral activity against several RNA and DNA viruses, associates with the endoplasmic reticulum (ER) and Golgi apparatus. We provide data to correct this misinterpretation and further report that MxA forms membraneless metastable (shape-changing) condensates in the cytoplasm consisting of variably sized spherical or irregular bodies, filaments, and even a reticulum. Remarkably, MxA condensates showed the unique property of rapid (within 1 to 3 min) reversible disassembly and reassembly in intact cells exposed sequentially to hypotonic and isotonic conditions. Moreover, GFP-MxA condensates included the VSV nucleocapsid (N) protein, a protein previously shown to form liquid-like condensates. Since intracellular edema and ionic changes are hallmarks of cytopathic effects of a viral infection, the tonicity-driven regulation of MxA condensates may reflect a mechanism for modulation of MxA function during viral infection.

SPERMATOCYTE GRANULES IN DROSOPHILA MELANOGASTER

1969 ◽  
Vol 11 (1) ◽  
pp. 153-168 ◽  
Author(s):  
John Erickson ◽  
A. B. Acton
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Drosophila Melanogaster ◽  
Host Cell ◽  
Acridine Orange ◽  
Meiotic Drive ◽  
Adult Males ◽  
Unit Membrane ◽  
The Third ◽  
The Individual

Granular inclusions are found in testes from a cn bw stock of Drosophila melanogaster, and maternally derived lines, such as SD. In late larval and early pupal stages, these granules show a polarized distribution within primary spermatocytes corresponding to the polarity basic to the type of meiotic drive where certain homologues reach that pole of the spermatocyte leading to functional sperm. In adult males, the granules are found in intercellular patches in the testes. Electron microscopy shows the spermatocyte granules to be spheroids of about 0.7 μ; dividing, or double forms resulting from division, are about 1.8 μ long. They contain numbers of ribosome-like particles and fine strands presumed to be DNA. The acridine orange test for nucleic acids was positive. Each granule is surrounded by two layers of unit membrane and a third such membrane envelopes the individual or the pair of granules, as the case may be. The third membrane layer (and additional membranes sometimes seen) is thought to be due to entrance of the granules into the host cell through the cisternae of the endoplasmic reticulum. Transmission of the granules is strictly maternal and independent of chromosome constitution. Transmission by contagion was not found. Spermatocyte granules are not requisite to the effectiveness of the SD meiotic drive system, which regularly carries them. A slightly lowered fertility of females carrying the granules was found but no similar effect is produced in males. The evidence suggests that they are parasitic organisms, probably Rickettsiae.

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