ULTRASTRUCTURE OF BACTERIZED AND AXENIC TROPHOZOITES OF <i>ENTAMOEBA HISTOLYTICA</i> WITH PARTICULAR REFERENCE TO HELICAL BODIES

Rosenbaum, Robert M.; Wittner, Murray

doi:10.1083/jcb.45.2.367

Cited by 89 publications

(31 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This conclusion is in conflict with earlier reports that E. histolytica lacks a continuous ER compartment, which were based on work conducted with fixed amebic trophozoites (6,8,11,13,16). The inability to detect a continuous ER compartment in prior studies presumably was an artifact of fixation.…”

contrasting

confidence: 55%

“…Beyond its medical importance, E. histolytica has several unusual features that are of interest to evolutionary biologists. It is a structurally simple eukaryote, lacking mitochondria and peroxisomes and having no recognizable Golgi complex or rough endoplasmic reticulum (ER) (6,11,16). Some have hypothesized that E. histolytica diverged from other eukaryotic lineages prior to the development of these structures (2).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Evidence of a Continuous Endoplasmic Reticulum in the Protozoan Parasite Entamoeba histolytica

Teixeira

Huston

2008

Eukaryot Cell

View full text Add to dashboard Cite

show abstract

contrasting

confidence: 55%

mentioning

confidence: 99%

Evidence of a Continuous Endoplasmic Reticulum in the Protozoan Parasite Entamoeba histolytica

Teixeira

Huston

2008

Eukaryot Cell

View full text Add to dashboard Cite

show abstract

“…Comparison of arrays seen in longitudinal and cross sections showed the ordering of helices to be the same in both trophozoites and cysts. There was no evidence that helices formed at specific sites in the cell or about microfilaments, as has been suggested by others (22,12,19).…”

Section: Inhibitor-stim Ulated Ribosome Aggregationmentioning

confidence: 50%

“…We have noted in the literature and in our own studies a correspondence between the appearance of aggregates in trophozoites and periods of reduced metabolic activity. For example, in one report (1) the number of aggregates was seen to increase with culture age, and in another (22), slow-growing trophozoites were found to contain more helical arrays than rapidly growing cells, in our own work we have observed that particles with the staining properties of chromatoid bodies frequently appear in trophozoites which have entered stationary growth phase and disappear when the amebas are transferred to fresh growth medium. Of course, in cysts, which probably represent the metabolic ebb in the Entamoeba life cycle, virtually all the ribosomes are aggregated (2, 13).…”

mentioning

confidence: 72%

The mechanism of formation of inhibitor-induced ribosome helices in Entamoeba invadens.

Kusamrarn¹,

Sobhon²,

Bailey³

1975

The Journal of Cell Biology

View full text Add to dashboard Cite

Helices and aggregates of helices (chromatoid bodies) composed of ribosomelike particles appear in cysts and slow-growing trophozoites of Entamoeba invadens. We found that similar helix aggregates were formed abundantly in actively growing E. invadens trophozoites treated with a variety of direct or indirect inhibitors of protein synthesis. The inhibitor-induced helices appeared cytochemically and ultrastructurally identical to those seen in cysts.Numerous single helices and small arrays occurred randomly distributed throughout the trophozoite cytoplasm within 15 rain after treatment with NaF, which rapidly and completely stopped all nucleic acid and protein synthesis. Cycloheximide (CH), which inhibited protein synthesis as effectively as NaF, stimulated aggregate formation more slowly, and only after a delay of 30-60 rain. CH temporarily blocked NaF-stimulated aggregate formation. Aggregation was slowest with actinomycin-D, which strongly inhibited RNA synthesis but depressed protein synthesis only slowly. These results suggested that release of ribosomes from mRNA was required for aggregation.Inhibition by CH was reversible, and aggregates disappeared from CH-treated amebas shortly after they were transferred to inhibitor-free growth medium. There was no evidence that helices assembled about a structural organizer within the cell or that the process involved metabolic activity. It was concluded that the inhibitor-induced helices were composed of mature, normally functional ribosomes and that helix formation was a spontaneous and reversible consequence of the accumulation within the cell of free monosomes (or subunits) which were prevented from binding to mRNA.Considerable evidence has accumulated which indicates that the aggregated ribonucleoprotein helices (chromatoid bodies) found in cysts of Entamoeba are composed of ribosomal particles (18,14,15). There are, however, uncertainties about the precise structural and functional nature of the unit particles within the helices and about the total composition of the arrays of helices.

show abstract

“…As ancient eukaryotes, Entamoeba parasites contain only rudimentary endoplasmic reticulum and Golgi apparatus (2,3). Despite this, vesicle trafficking pathways appear to be essential to the pathogenesis of these parasites as (i) uptake and digestions of nutrients by mature trophozoites in the large intestine, (ii) invasion of the intestinal epithelium, (iii) delivery of cyst wall components during encystation, and (iv) dissemination and establishment of extra-intestinal infections all rely on endocytosis and secretion.…”

mentioning

confidence: 99%

Identification and Biochemical Characterization of Unique Secretory Nucleases of the Human Enteric Pathogen, Entamoeba histolytica

McGugan

Joshi

Dwyer

2007

Journal of Biological Chemistry

View full text Add to dashboard Cite

The ancient eukaryotic human pathogen, Entamoeba histolytica, is a nucleo-base auxotroph (i.e. lacks the ability to synthesize purines or pyrimidines de novo) and therefore is totally dependent upon its host for the supply of these essential nutrients. In this study, we identified two unique 28-kDa, dithiothreitol-sensitive nucleases and showed that they are constitutively released/secreted by parasites during axenic culture. Using several different molecular approaches, we identified and characterized the structure of EhNucI and EhNucII, genes that encode ribonuclease T2 family proteins. Homologous episomal expression of epitope-tagged EhNucI and EhNucII chimeric constructs was used to define the functional and biochemical properties of these released/secreted enzymes. Results of coupled immunoprecipitation-enzyme activity analyses demonstrated that these "secretory" enzymes could hydrolyze a variety of synthetic polynucleotides, as well as the natural nucleic acid substrate RNA. Furthermore, our results demonstrated that sera from acutely infected amebiasis patients recognized and immunoprecipitated these parasite secretory enzymes. Based on these observations, we hypothesize that within its host, these secretory nucleases could function, at a distance away from the parasite, to harness (i.e. hydrolyze/access) host-derived nucleic acids to satisfy the essential purine and pyrimidine requirements of these organisms. Thus, these enzymes might play an important role in facilitating the survival, growth, and development of this important human pathogen.The ancient eukaryotic human parasite, Entamoeba histolytica, is the causative agent of invasive amebiasis in humans infecting 10% of the world population and resulting in over 100,000 deaths annually, chiefly from amebic liver abscess (1). Infection is acquired through the ingestion of the quadranucleate cyst form of the organism from fecally contaminated food or water supplies. Excystation occurs in the small intestine, releasing immature trophozoites, which move into and colonize the nutrient-poor large intestine.As ancient eukaryotes, Entamoeba parasites contain only rudimentary endoplasmic reticulum and Golgi apparatus (2, 3). Despite this, vesicle trafficking pathways appear to be essential to the pathogenesis of these parasites as (i) uptake and digestions of nutrients by mature trophozoites in the large intestine, (ii) invasion of the intestinal epithelium, (iii) delivery of cyst wall components during encystation, and (iv) dissemination and establishment of extra-intestinal infections all rely on endocytosis and secretion. In addition, these parasites lack many traditional eukaryotic biochemical pathways, including the de novo biosynthesis of purine and pyrimidine nucleobases. As a result, these parasites are completely dependent upon their host for the supply of these essential preformed nutrients. In that regard, it has been reported previously that Entamoeba are capable of salvaging both purines and pyrimidines from the extracellular milieu during in vit...

show abstract

ULTRASTRUCTURE OF BACTERIZED AND AXENIC TROPHOZOITES OF ENTAMOEBA HISTOLYTICA WITH PARTICULAR REFERENCE TO HELICAL BODIES

Cited by 89 publications

References 25 publications

Evidence of a Continuous Endoplasmic Reticulum in the Protozoan Parasite Entamoeba histolytica

Evidence of a Continuous Endoplasmic Reticulum in the Protozoan Parasite Entamoeba histolytica

The mechanism of formation of inhibitor-induced ribosome helices in Entamoeba invadens.

Identification and Biochemical Characterization of Unique Secretory Nucleases of the Human Enteric Pathogen, Entamoeba histolytica

Contact Info

Product

Resources

About