Electron microscope observations on intracellular virus-like particles associated with the cells of the Lucké renal adenocarcinoma

Tissue-derived extracellular vesicles in cancer progression: mechanisms, roles, and potential applications

Extracellular vesicles (EVs) are small lipid bilayer-enclosed vesicles that mediate vital cellular communication by transferring cargo between cells. Among these, tissue-derived extracellular vesicles (Ti-EVs) stand out due to their origin from the tissue microenvironment, providing a more accurate reflection of changes in this setting. This unique advantage makes Ti-EVs valuable in investigating the intricate relationship between extracellular vesicles and cancer progression. Despite considerable research efforts exploring the association between Ti-EVs and cancers, a comprehensive clustering or grouping of these studies remains lacking. In this review, we aim to fill this gap by presenting a comprehensive synthesis of the mechanisms underlying Ti-EV generation, release, and transport within cancer tissues. Moreover, we delve into the pivotal roles that Ti-EVs play in cancer progression, shedding light on their potential as diagnostic and therapeutic tools. The review culminates in the construction of a comprehensive functional spectrum of Ti-EVs, providing a valuable reference for future research endeavors. By summarizing the current state of knowledge on Ti-EVs and their significance in tumor biology, this work contributes to a deeper understanding of cancer microenvironment dynamics and opens up avenues for harnessing Ti-EVs in diagnostic and therapeutic applications.

Extracellular vesicles: A dive into their role in the tumor microenvironment and cancer progression

Extracellular vesicles (EVs) encompass a diverse set of membrane-derived particles released from cells and are found in numerous biological matrices and the extracellular space. Specific classes of EVs include apoptotic bodies, exosomes, and microvesicles, which vary in their size, origin, membrane protein expression, and interior cargo. EVs provide a mechanism for shuttling cargo between cells, which can influence cell physiology by transporting proteins, DNA, and RNA. EVs are an abundant component of the tumor microenvironment (TME) and are proposed to drive tumor growth and progression by communicating between fibroblasts, macrophages, and tumor cells in the TME. The cargo, source, and type of EV influences the pro- or anti-tumoral role of these molecules. Therefore, robust EV isolation and characterization techniques are required to ensure accurate elucidation of their association with disease. Here, we summarize different EV subclasses, methods for EV isolation and characterization, and a selection of current clinical trials studying EVs. We also review key studies exploring the role and impact of EVs in the TME, including how EVs mediate intercellular communication, drive cancer progression, and remodel the TME.

Cancer in Amphibia, a rare phenomenon?

Compared to other animals, the spontaneous occurrence of tumors in wild amphibians is relatively rare, generally limited to specific populations or species. The number of reports of spontaneous tumors in amphibians known up to 1986 was 491 cases in anurans and about 253 cases in urodeles. Similarly, there have been many, unsuccessful attempts to chemically or biologically induce tumors in amphibians. With these considerations, it is inevitable to wonder: do urodeles and anurans have an inherent resistance to cancer? Here, we review the spontaneous and induced occurrence of tumors in amphibians in a timeline, as well as failed attempts to induce tumors in these amphibians. Indeed, recent studies seem to indicate that there is a relationship between regeneration and cancer because regenerating tissues seem to resist tumorigenesis, as opposed to nonregenerative tissues of the same amphibian models. Although the mechanisms that allow regenerating tissues to resist tumorigenesis have not been elucidated, it is worth to note that, in addition to the apparent relationship between regeneration and cancer, amphibians possess characteristics that could contribute to their ability to resist the development of neoplastic events. The implications of these features in cancer susceptibility are discussed.

A brief history of nearly EV-erything - The rise and rise of extracellular vesicles

Extracellular vesicles (EVs) are small cargo-bearing vesicles released by cells into the extracellular space. The field of EVs has grown exponentially over the past two decades; this growth follows the realisation that EVs are not simply a waste disposal system as had originally been suggested by some, but also a complex cell-to-cell communication mechanism. Indeed, EVs have been shown to transfer functional cargo between cells and can influence several biological processes. These small biological particles are also deregulated in disease. As we approach the 75th anniversary of the first experiments in which EVs were unknowingly isolated, it seems right to take stock and look back on how the field started, and has since exploded into its current state. Here we review the early experiments, summarise key findings that have propelled the field, describe the growth of an organised EV community, discuss the current state of the field, and identify key challenges that need to be addressed.

Virus-Like Particle: Evolving Meanings in Different Disciplines

Virus-like particle (VLP) is a term that has been in use for about 80 years. Usually, VLP has meant a particle that is like a virus, generally by appearance, but without either proven or actual virus functionality. Initially VLP referred to particles seen in electron microscope images of tissues. More recently, VLP has come to mean other things to other researchers. A key divergence has been use of VLP in association with vaccine and biotechnology applications versus use of VLP in enumeration of viruses in environmental samples. To these viral ecologists, a VLP is a particle that is virus sized, has nucleic acid, and could be a functional virus. But to vaccine developers and biotechnology researchers a VLP instead is a viral structure that intentionally lacks a viral genome. In this study, we look at the history of use of VLP, following changes in meaning as the technology to study VLPs changed.

Isolation of extracellular vesicles with combined enrichment methods

Extracellular vesicles (EVs) are currently of tremendous interest in many research disciplines and EVs have potential for development of EV diagnostics or therapeutics. Most well-known single EV isolation methods have their particular advantages and disadvantages in terms of EV purity and EV yield. Combining EV isolation methods provides additional potential to improve the efficacy of both purity and yield. This review assesses the contribution and efficacy of using combined EV isolation methods by performing a two-step systematic literature analysis from all papers applying EV isolation in the year 2019. This resulted in an overview of the various methods being applied for EV isolations. A second database was generated for all studies within the first database that fairly compared multiple EV isolation methods by determining both EV purity and EV yield after isolation. From these databases it is shown that the most used EV isolation methods are not per definition the best methods based on EV purity or EV yield, indicating that more factors play a role in the choice which EV isolation method to choose than only the efficacy of the method. From the included studies it is shown that ~60% of all the included EV isolations were performed with combined EV isolation methods. The majority of EV isolations were performed with differential ultracentrifugation alone or in combination with differential ultrafiltration. When efficacy of EV isolation methods was determined in terms of EV purity and EV yield, combined EV isolation methods clearly outperformed single EV isolation methods, regardless of the type of starting material used. A recommended starting point would be the use of size-exclusion chromatography since this method, especially when combined with low-speed centrifugation, resulted in the highest EV purity, while still providing a reasonable EV yield.

Virus-Host Coevolution with a Focus on Animal and Human DNA Viruses

Viruses have been infecting their host cells since the dawn of life, and this extremely long-term coevolution gave rise to some surprising consequences for the entire tree of life. It is hypothesised that viruses might have contributed to the formation of the first cellular life form, or that even the eukaryotic cell nucleus originates from an infection by a coated virus. The continuous struggle between viruses and their hosts to maintain at least a constant fitness level led to the development of an unceasing arms race, where weapons are often shuttled between the participants. In this literature review we try to give a short insight into some general consequences or traits of virus–host coevolution, and after this we zoom in to the viral clades of adenoviruses, herpesviruses, nucleo-cytoplasmic large DNA viruses, polyomaviruses and, finally, circoviruses.

Cancer Resistance in Amphibians

While spontaneous tumours may occasionally develop in inbred and isogenic strains of Xenopus laevis, the South African clawed toad, they are extremely rare in natural and laboratory populations. Only two amphibian neoplasms, the renal adenocarcinoma of Rana pipiens and the lymphosarcoma of Xenopus laevis, have been extensively explored. Amphibians are resistant to the development of neo-plasia, even following exposure to “direct-acting” chemical carcinogens such as N-methyl- N-nitrosourea, that are highly lymphotoxic, thus diminishing immune reactivity. Regenerative capacity in adults, and a dramatic metamorphosis which remodels much of the larval body to produce the adult form, are unique to amphibian vertebrates, and the control mechanisms involved may protect against cancer. For example, naturally rising corticosteroid titres during metamorphosis will impair some T-cell functions, and the removal of T-regulatory (suppressor) functions inhibits the induction of altered-self tolerance. Altered-self tolerance is not as effectively induced in adult Xenopus laevis as in mammals, so cancer cells with new antigenicity are more likely be rejected in amphibians. Amphibian immunocytes tend to undergo apoptosis readily in vitro, and, unlike mammalian immunocytes, undergo apoptosis without entering the cell cycle. Cells not in the cell cycle that die from nuclear damage (apoptosis), will have no opportunity to express genetic instability leading to cell transformation. We suggest that all these factors, rather than any one of them, may reduce susceptibility to cancer in amphibians.

Cyprinid Herpesvirus 3: An Archetype of Fish Alloherpesviruses

The order Herpesvirales encompasses viruses that share structural, genetic, and biological properties. However, members of this order infect hosts ranging from molluscs to humans. It is currently divided into three phylogenetically related families. The Alloherpesviridae family contains viruses infecting fish and amphibians. There are 12 alloherpesviruses described to date, 10 of which infect fish. Over the last decade, cyprinid herpesvirus 3 (CyHV-3) infecting common and koi carp has emerged as the archetype of fish alloherpesviruses. Since its first description in the late 1990s, this virus has induced important economic losses in common and koi carp worldwide. It has also had negative environmental implications by affecting wild carp populations. These negative impacts and the importance of the host species have stimulated studies aimed at developing diagnostic and prophylactic tools. Unexpectedly, the data generated by these applied studies have stimulated interest in CyHV-3 as a model for fundamental research. This review intends to provide a complete overview of the knowledge currently available on CyHV-3.

A Study of the early stages of infection with the tipula iridescent virus

Ultra-thin sections and electron microscopy have been used in a study of the empty membranes which occur in the fatbody cells of the larva of T. paludosa infected with the Tipula Iridescent Virus (TIV).

It has been observed that these empty membranes are most numerous in the early stages of infection. Later an apparent ‘primary body’, which may be threadlike in its initial stages, develops in the centre of the membrane. This primary body seems to increase in size until the membrane is filled, and the various steps in this process can easily be seen.

It is suggested that the formation of the empty membranes and the apparent gradual development of their contents are the means by which the virus multiplies.

The remarkable resemblance between the empty virus membranes and the endoplasmic reticulum is pointed out.

Historical background

The persisting ancient view of cancer as a contagious disease ended with 19th century scientific investigations which seemed to show it was not. The resulting dogma against an infectious cause for cancer produced great prejudice in the scientific community against the first report of an oncogenic virus by Rous early in the 20th century and, even in the 1950s, against Gross's finding of a murine leukaemia virus and a murine virus causing solid tumours. The Lucké frog renal carcinoma virus was the first cancer-associated herpesvirus. Intriguingly, an environmental factor, ambient temperature, determines virus genome expression in the poikilothermic frog cells. Although an alpha-herpesvirus, Marek's disease virus of chickens shares some aspects of biological behaviour with Epstein-Barr virus (EBV) of man. Very significantly, its lymphomas are the first naturally occurring malignancy to be controlled by an antiviral vaccine, with implications for human virus-associated cancers. The circumstances and climate of opinion in which successive gamma-herpesviruses were discovered are described. The identification of EBV involved two unconventionalities: its finding in cultured Burkitt's lymphoma cells when no human lymphoid cell had ever been maintained in vitro, and its recognition in the absence of biological activity by the then new technique of electron microscopy. These factors engendered hostility to its acceptance as a new human tumour-associated virus. The EBV-like agents of Old World apes and monkeys and the T-lymphotropic gamma-herpesviruses of New World monkeys were found at about the same time, not long after the discovery of EBV. For many years these were thought to be the only gamma-herpesviruses of non-human primates; however, very recently B-lymphotropic EBV-like agents have been identified in New World species as well. Mouse herpesvirus 68 came to light by chance during a search for arboviruses and has become important as a laboratory model because of its close genetic relatedness to EBV and its comparable biological behaviour. The discovery of Kaposi's sarcoma-associated herpesvirus six years ago was made using unconventional new methods, but, unlike with EBV 30 years before, this did not hinder its acceptance. This contrast is discussed in the context of the great progress in human tumour virology which has been made in recent years.

Common metastatic carcinoma of California sea lions (Zalophus californianus): evidence of genital origin and association with novel gammaherpesvirus

Tissues from 10 adult California sea lions (Zalophus californianus, seven females and three males) that had metastatic carcinoma in sublumbar area lymph nodes were examined histologically. A distinctive epithelial proliferative lesion interpreted as intraepithelial neoplasia was found in genital tracts of all ten animals; in vagina (5/7), cervix (7/7), uterus (3/7), penis (3/3) and prepuce (3/3). Intraepithelial neoplasia closely resembled metastatic carcinomas and was directly contiguous with invasive carcinoma in one animal. Rare eosinophilic intranuclear inclusion bodies were found in penile and preputial intraepithelial neoplasia (one animal), cervical intraepithelial neoplasia (one animal), invasive cervical carcinoma (one animal) and metastatic carcinoma (two animals). Electron microscopic examination of tissues from two sea lions (one with intraepithelial neoplasia and one with metastatic carcinoma) demonstrated viral particles consistent with a herpesvirus. An immunohistochemical stain for the latent membrane protein of Epstein-Barr virus was positive in intraepithelial neoplasia in one sea lion. Herpesvirus DNA sequences were detected by consensus primer polymerase chain reaction (PCR) in metastatic carcinomas from all four sea lions from which unfixed tumor samples were available. Results of sequencing were consistent with a novel gammaherpesvirus in the genus Rhadinovirus. DNA extracted from the four metastatic carcinomas also was tested for papillomavirus by Southern blot and PCR with consensus papillomavirus primers; all samples were negative by both methods. These findings support the genital origin of the sea lion carcinoma and implicate a novel gammaherpesvirus as a possible cause.

Electron microscopic observations on the development of herpes simplex virus

Study of the J.M. strain of herpes simplex virus in human amnionic and HeLa cell tissue cultures revealed the presence of intranuclear crystals composed of viral particles with a single membrane enclosing a central body. Randomly dispersed virus with double coats was seen in the nuclear matrix and between multiple membranes at the nuclear periphery. The majority of intracytoplasmic viral particles were within walled vacuoles. It is suggested that this strain of virus differentiates and frequently crystallizes at template sites which are characterized by aggregates of granules near the nuclear margin; that particles, either singly or occasionally in small groups, become enclosed by a second peripheral membrane while still within the nucleus; that the virus can pass into the cytoplasm through reduplications of the nuclear membrane which are deposited behind the virus in such a manner as to prevent rupture of the nucleus; that most of the intracytoplasmic virus is contained within sacks formed by nuclear membranes; and that rupture of these sacks at the cell surface results in extrusion of virus without disruption of the cell. No evidence was obtained to support the hypothesis that virus develops in the cytoplasm. Examination of the H.R. and C.G. strains of herpes simplex virus in identical cell lines grown under similar conditions failed to show viral crystals, but reduplication of the nuclear membranes was evident. Study of the J.M. strain in cells of chicken embryo chorioallantoic membranes indicated that the basic mechanisms of viral development and release did not differ from those operating in HeLa and human amnionic cells.

A new mouse virus causing necrosis of the thymus in newborn mice

A new mouse virus has been recovered from laboratory and wild mice. The agent induces a non-fatal disease in infant mice, characterized by acute massive necrosis of the thymic medulla and cortex, granulomatous reaction, and subsequent restoration of essentially normal architecture with scarring. Intranuclear inclusion bodies are produced. Virus may persist in tissues of convalescent mice for many months. Electron micrographs of acutely infected thymuses showed nuclear and cytoplasmic karyoannular particles and masses of parallel fibrils in nuclei.

Structure and development of viruses as observed in the electron microscope. V. Western equine encephalomyelitis virus

Stages in the development and release of Western equine encephalomyelitis virus are illustrated and described. It is suggested that precursor particles 22 mmicro in diameter differentiate at template sites close to membranes bordering cytoplasmic vacuoles and that these particles either pass into the lumen of the vacuole, acquiring in the process a coat and peripheral membrane, or are dispersed in the cytoplasm and extruded through the cellular wall, emerging as viral particles on the surface. Although necrosis and dissolution of the cell with release of contents, including virus, may intervene at any stage of infection, ejection of virus from the vacuoles presumably can occur without rupture of the cell. The virus consists of a 30 mmicro core separated by a zone of lesser density from a sharply defined peripheral membrane 45 to 48 mmicro in diameter. Precursor particles, as well as viral particles, occasionally crystallize, the former in the cytoplasm, the latter in vacuoles and probably on the cellular surface.

MORPHOLOGICAL AND BIOLOGICAL STUDIES ON A VIRUS IN CULTURED LYMPHOBLASTS FROM BURKITT'S LYMPHOMA

Lymphoblasts of two tissue culture strains (EB1 and EB2) from different biopsy specimens of Burkitt's lymphoma have been examined in thin sections by electron microscopy, and have each been found to carry a morphologically identical virus. The virus was observed in samples taken over many months, being present in about 1 to 2 per cent of the cells in two forms: Immature particles about 75 mmicro in diameter which were seen in both the nucleus and cytoplasm; and larger mature particles with a diameter of 110 to 115 mmicro, which were either within membrane-bounded cytoplasmic spaces or at the cell surface. There was some indication that the particles matured by budding through the cytoplasmic membranes. Both types of particle occurred in dead degenerating cells or, less frequently, in intact altered cells. The characteristic alterations of the latter included margination of the chromatin, fragmentation of the nuclear envelope, beaded opaque material in the mitochondria, and, with one of the cell strains (EB1), sheaves of altered spindle tubules. All attempts to isolate and identify the virus carried by the two strains of lymphoblasts failed. No pathological effects were caused in 8-day chick embryos inoculated either with whole lymphoblasts or extracts of disrupted lymphoblasts, using the intraallantoic, amniotic, and chorioallantoic routes, and the extraembryonic fluids of such chicks were without haemagglutinating activity for human, chicken, guinea pig, or monkey erythrocytes. Whole lymphoblasts or lymphoblast extracts were likewise without effect when inoculated intraperitoneally into newborn hamsters or two strains of newborn mice. Similar lymphoblast inocula did not cause detectable changes in 9 different test tissue culture systems even after 8 blind passages. The nature of the unknown, unidentified virus in the cultured lymphoblasts from Burkitt's lymphomas is considered and its possible relationship to the cells discussed.

Temperature-dependent metastasis of the Lucke renal carcinoma and its significance for studies on mechanisms of metastasis

Metastasis is temperature dependent in the renal adenocarcinoma of the North American leopard frog, Rana pipiens. Widespread, multiple, metastatic colonies occur in tumor-bearing frogs kept at 28 degrees C for 50 days while tumor-bearing frogs kept at 7 degrees C for 98 days or more have either no secondary deposits or they have only an occasional small metastatic nodule. An attractive aspect of the frog tumor is that invasion and metastasis can be permitted or inhibited by the manipulation of temperature alone-no exogenous chemicals or drugs are required for the effect. Because of this, biological variables which reproducibly and specifically associate with metastasis permissive conditions when ambient temperature is cycled between permissive and inhibitory values are strong candidates for being causal elements in the multistep process leading to metastasis. Intravascularly injected labelled renal tumor cells reached all organs studied in as little as 15 minutes at both metastasis restrictive and permissive temperature. The results with tumor cell inoculation dispose of the possibility that failure of metastasis in chilled animals is due to cold-induced changes in blood flow. Histologically typical metastatic colonies developed in frogs, kept at the permissive temperature, after injection with disaggregated tumor cells which were previously cryopreserved. Frog tumors elaborate type I collagenase in a temperature dependent manner. Type IV collagenase has been demonstrated as well. Tumor cell detachment in vitro, assembly and disassembly of tumor cell cytoplasmic microtubules, and invasion in vitro, are all temperature dependent.

Herpesviruses in metastatic Lucké renal adenocarcinoma

The etiologic agent of the renal adenocarcinoma of leopard frogs, Rana pipiens, is the Lucké tumor herpesvirus (LTHV). The virus is easily detected with thin section electron microscopy in primary tumors of frogs which have been exposed to a cold environment. Several spontaneous metastatic nodules and a large primary tumor were detected at autopsy of a frog which had been maintained at 4 degrees C for 73 days. LTHV was found not only in the primary tumor, as previously reported, but also was present in metastatic tumor cells in the liver, fat body, and bladder. The presence of LTHV in metastatic cells demonstrates that the differentiated state of primary Lucké tumor cells is retained in its metastatic colonies even at the fine structure level revealed by electron microscopy.

Detection of Lucké herpes virus antigens in infected frog pronephric cells

A frog pronephric cell line, infected with herpes virus derived from Lucké renal carcinomas of Rana pipiens was examined for the presence of Lucké herpes virus antigens. Non-infected pronephric cells were controls. Antiserum to purified Lucké tumor herpes virus was applied in blind tests to the normal and virus infected cells. Both cytoplasmic and nuclear fluorescence was found in the herpes virus infected cells after indirect immunofluorescence with the antiserum. Infected cells cultivated at the optimum growth temperature of 25 degrees C or maintained at 9 degrees C, a temperature inducive to herpes virus replication, showed equivalent fluorescence reactions. No fluorescence was found in the normal pronephric cell line. Examination of parallel herpes infected cells showed cytopathic effect in monolayers by light microscopy, and nuclear or cytoplasmic immunofluorescence. Electron microscopic examination revealed proviral elements in nuclei and sparsely scattered herpes virus coincident with cytoplasmic fluorescence.

[Viruses, virus-like and virus-related structures in nasopharyngeal carcinoma (author's transl)]

Five cases of nasopharyngeal carcinoma with typically elevated EB-virus-antigen-titer were studied by light- and electron microscopic methods. Within the cytoplasm corona viruses in different forms, regular capsid-like particles with a diameter of 60 nm, tubuloreticular aggregates, and pathologic alterations of the membranes of the endoplasmatic reticulum could be found. The nuclei of the tumour cells often showed particles within the nucleoplasm with an average diameter of 100 nm containing a central core; the appearance of the particles is similar to that of herpes viruses as shown in the literature concerning EB-viruses. Atypic mitoses are common as well as free nucleoplasma-like condensates within the ground cytoplasm. Multiple doubling of the membranes of the endoplasmatic reticulum are characteristic for the tumor cell cytoplasm. Myelin figures are often situated within the enlarged tubules of the E. R., within mitochondria and within the nuclei. The results are discussed concerning the possible viral etiology of nasopharyngeal carcinoma. We do not believe that the particles found within the nucleoplasm have a relation to nuclear pores. The arguments are discussed.

Light and electron microscopic investigations of nasopharyngeal carcinomas with regard to the viral etiology of these tumors

Five carcinomata of the nasopharynx (four lymphoepithelial carcinomata of the Regaud type and one squamous cell carcinoma) were examined light and electron microscopically. In addition to the familiar histological and cytological features of these tumors, and because of an increased antibody titer against Epstein-Barr virus in all five patients, all those cytoplasmic and nuclear inclusions were examined which could be interpreted as indicative of a virus contact. The following structures were found: 1. Particles and microtubules which correspond in diameter, shape, and location to Corona viruses. 2. Particles surrounded by a double membrane and resembling in form and diameter Oncorna viruses. 3. Tubulo-reticular, coil-shaped cytoplasmic inclusions interpreted as an unspecific reaction of the host cell to viral attack. 4. Spherical nuclear bodies, which are frequently observed in tumors and in viral infections. 5. Intranuclear particles which correspond in diameter, structure, and distribution to viruses of the herpes type such as have been described in cell cultures of Burkitt lymphoma and nasopharyngeal carcinoma. The fifth group particularly was discussed in detail with regard to differentiation between those particles and other structures which could simulate a virus structure. Together with the appearance of increased ribosomes and of particular chromatin distribution within the tumor cell nuclei, the particles we discussed have been interpreted as morphological indications of a virus etiology of the examined tumors.

Recognition of virally transformed cells by lymphocytes from patients with prostatic cancer

Data presented describe the first assay using human peripheral blood lymphocytes (PBL) against two unique virally transformed cell lines in vitro. Human cells transformed by a cytomegalovirus (CMV-Mj) isolated from normal human prostate tissue were used as target cells in microcytoxicity assays with lymphocytes from 100 patients. Three target cell types were used: control human embryonic lung cells (HEL), transformed HEL cells (CMV-Mj-HEL-2), and transformed HEL cells retrieved from tumors induced in athymic nude mice (CMV-Mj-HEL-2, T-1) by injection of CMV-Mj-HEL-2 cells. PBL preparations from 84% of all patients tested significantly killed CMV-Mj-HEL-2, T-1 cells. However, only PBL from patients with prostatic carcinoma were cytotoxic for CMV-Mj-HEL-2 cells significantly more often than for control HEL. The implications of this approach are discussed.

Viral particles in nasopharyngeal carcinoma

Lymphoepithelioma of the nasopharynx was identified in a 17-year-old Chinese male. The Epstein-Barr virus titer was 1:3200. Tissue from the tumor mass was prepared for electron microscopy. Particles consistent with the morphological characteristics of herpes virus were found within the cytoplasm of malignant epithelial cells. This finding is discussed in relation to other data suggesting an oncogenic role of herpes virus in human malignancy.

Viral carcinogenesis in a pronephric cell line. An ultrastructural study

Herpesvirus recovered from cell fractions of the spontaneous Lucké renal tumor of adult Rana pipiens were used to infect a cell line derived from pronephroi of the same species. Viruses and virus-associated structures previously found in the primary renal tumor were observed, including nuclear inclusions of capsids with single or double membranes and capsids with nucleoids often within nuclear sacs. Embedded within the clumped and marginated chromatin were 55-nm tubular elements and associated unit membrane structures. Virus-associated, 35-nm tubular elements were also seen. The cytoplasm contained single, enveloped nucleoid virus and clusters of virus within cytoplasmic vesicles. Other cytoplasmic inclusions were dense, virus-associated, 25-nm filaments, virus particles within myeloid bodies, and possible viral budding from tubular organelles.

The nuclear membranes in hypertrophied human cardiac muscle cells

Nuclear membranes of cardiac muscle cells were studied in 134 patients with cardiac hypertrophy of various causes. Abnormalities observed consisted of: a) increased foldings and convolutions; b) nuclear pseudoinclusions formed by cytoplasmic organelles protruding into saccular invaginations of the nuclear membranes, and c) intranuclear tubules. The increased foldings and convolutions of the nuclear membranes and the nuclear pseudoinclusions appear to result from synthesis of nuclear membranes in excess of that needed to accommodate the increase in nuclear volume which occurs in hypertrophy. Intranuclear tubules were found in 6 patients and consisted of tubular invaginations, 400 to 650 A in diameter, of the inner nuclear membranes into the nucleoplasm. Some of these tubules were straight and cylindrical, and were associated with a peripheral layer of marginated chromatin; others were not associated with chromatin, appeared coiled and followed irregular courses. Intranuclear tubules in cardiac muscle cells probably represent an extreme cellular response to the stimulus of hypertrophy.

Neoplasms, differentiations and mutations

Evidence has been presented to support the concept that malignant tumors are postembryonic differentiations superimposed upon the process of tissue maintenance and renewal. Malignant stem cells are derived from normal stem cells. They have a capacity for proliferation and differentiation that operates at a different level of control than the normal. Even so, malignant stem cells are responsive to enviornmental control, suggesting that it may be possible to direct their differentiation or at least to control their ability to replicate. A tumor is a caricature of normal tissue and appears undifferentiated because of the preponderance of undifferentiated proliferating stem cells in relationship to the number of cells that have differentiated and become benign.

Are viruses important in carcinogenesis?

The role of viruses in the etiology of animal cancers is fairly certain. Information derived under both natural and experimental conditions supports the concept that either DNA- or RNA-containing viruses can fulfill this function. The DNA-containing herpesviruses, especially the Epstein-Barr virus, are currently the primary objects of intense investigation concerning their role in human cancer. This article will focus on the properties of counterpart herpesviruses in lower animals as well as the human virus candidates with an assessment of the observations concerning their oncogenic potential.

Unusual intranuclear tubular structures associated with the maturation of Herpesvirus saimiri in monkey kidney cell cultures

Unusual intranuclear tubules have been observed in cultures of both African green monkey and owl monkey kidney cells infected with Herpesvirus saimiri; the material was studied in thin sections with the electron microscope. The tubules were seen in about 10% of virus-containing cells at the stage when the virus matured by budding at the nuclear membrane, measured 160-180 nm in diameter and up to 3.6 μm in length, were bounded by an outer "membrane" and contained beneath this an electron dense repeating structure arranged either as a coil or a series of evenly spaced rings. The morphology and significance of the tubules are discussed.

Oyster herpes-type virus

A herpes-type virus infection, the first to be found in an invertebrate animal, is reported in the oyster Crassostrea virginica. Intranuclear herpes-type viral inclusions were more prevalent in the oyster at elevated water temperatures of 28 degrees to 30 degrees C than at normal ambient temperatures of 18 degrees to 20 degrees C. The inclusions were associated with a lethal disease at the elevated temperatures.

Renal adenocarcinoma with intranuclear inclusions in an Arctic ground squirrel

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