Remarks on the ultrastructure of type A, B, and C virus particles

A PLPPV sequence in the p8 region of Gag provides late domain function for mouse mammary tumor virus

The late (L) domain sequence used by mouse mammary tumor virus (MMTV) remains undefined. Similar to other L domain-containing proteins, MMTV p8 and p14NC proteins are monoubiquitinated, suggesting L domain function. Site-directed mutagenesis of p8, PLPPV, and p14NC, PLPPL, sequences in MMTV Gag revealed a requirement only for the PLPPV sequence in virion release in a position-dependent manner. Electron microscopy of a defective Gag mutant confirmed an L domain budding defect morphology. The equine infectious anemia virus (EIAV) YPDL core L domain sequence and PLPPV provided L domain function in reciprocal MMTV and EIAV Gag exchange mutants, respectively. Alanine scanning of the PLPPV sequence revealed a strict requirement for the valine residue but only minor requirements for any one of the other residues. Thus, PLPPV provides MMTV L domain function, representing a fourth type of retroviral L domain that enables MMTV Gag proteins to co-opt cellular budding pathways for release.

Three new cases of R-type virus-like particles in hamster tumours

R-type virus-like particles (VLP) in fibrosarcoma and myeloid tumour induced in hamsters with the myeloleukaemic virus of Graffi and in hamster embryonic fibroblasts infected with the lympholeukaemic virus Ly/Ya are described. The particles are found in the cysternae of the rough surface endoplasmic reticulum (RER). The VLP are classified as endogenous virus (EV) whose expression is determined by the initial infection with murine leukaemia virus (MLV).

Diagnostic virology using electron microscopic techniques

This chapter illustrates the development of the use of electron microscopy in viral diagnosis. The field covered is confined to medical viral diagnosis, but parallel developments have taken place in both veterinary and botanical fields and techniques derived from both these sources are also included where relevant. It is reported that the scanning transmission mode of operation, which can induce image contrast changes electronically, may enhance studies with unstained sections and perhaps facilitate thin section immune electron microscopy (IEM). The application of negative stain IEM has been particularly useful for the study of the antigenic nature of some of the newly discovered noncultivable viruses. Viral antigens can also be detected in thin sections of infected cells by IEM with suitably labeled specific antibodies. Confirmation of viral infection by electron microscopy on tissues originally processed for light microscopy is also frequently useful.

Ultrastructural studies on Maedi-Visna virus

Ultrastructural studies of Maedi-Visna virus (MVV) particles isolated from tissue culture fluids of MVV-infected cells as well as cultured cells infected with MVV were performed. MVV particles aree bounded by an envelope with projections loosely attached to its surface. Virions contain a core (sometimes two or more) of conical or ovoid shape enclosing an electron-dense nucleoid which is much smaller in diameter than the core and which can only be seen in ultrathin sections. A distinct core shell is to be found in most of the ultrasectioned particles. Cores, liberated from the virions by detergent treatment, exhibited the same shape as their enveloped counterparts. Budding structures with crescents underlying the cell membrane without an intermediate space seem to be bordered on their cell side by an electron-dense thin layer. Particles obviously representing intervenig stages of viral maturation showing parts of the crescents at the viral membrane and empty core shells could be found in single cases.

Primary cerebral neuroblastoma: a light and electron microscopic study

A small-cell neoplasm in the left temporal lobe of a 10 and a half year old boy was studied by light and electron microscopy. Routine sections of the mass showed a differentiating neuroblastoma with Homer Wright rosettes, several foci of immature neoplastic neurons (ganglion cells), and many mitoses, areas of necrosis and tumor vessels showing endothelial proliferation. Ultrastructurally, most cells resembled early fetal neuroblasts and also were similar to those in murine and peripheral human neuroblastomas.

The development and degeneration of Purkinje cells in pcd mutant mice

Purkinje cell degeneration (pcd), an autosomal recessive mutation in the mouse, causes the postnatal death of virtually all cerebellar Purkinje cells during the third and fourth postnatal week. We have compared the postnatal development of normal and pcd mutant Purkinje cells. The early deviations from normal development involve primarily the perikaryonal polysomes and endoplasmic reticulum. Many of the mutant Purkinje cells retain abnormally the basal accumulation of polysomes, a finding which permits the identification of affected animals at postnatal day 15, one week prior to the onset of behavioral abnormalities. In addition, the affected Purkinje cells possess unusual configurations of endoplasmic reticulum with associated electron-dense particles similar to but larger than ribosomes, mature and forming intracisternal A particles and nematosomes. Before the pcd Purkinje cells degenerate they appear to receive all their appropriate synaptic contacts. Some disruption, however, of parallel fiber: Purkinje spine synaptogenesis occurs at late stages of development. Some spines lack presynaptic elements, postsynaptic thickenings are present along the dendritic shafts and parallel fibers appear to make synaptic contacts directly onto the shafts. The spectrum of early morphological changes that has been observed in pcd mutant Purkinje cells is thus far unique to this cerebellar abnormality.

Rauscher leukemia virus populations enriched for "immature" virions contain increased amounts of P70, the gag gene product

Preparations of Rauscher leukemia virus (RLV) that had relatively low, intermediate, or high levels of P70 (the gag gene product) on sodium dodecyl sulfatepolyacrylamide gel electrophoresis were examined by thin-section electron microscopy. A direct correlation was found between the number of immature virions in the RLV preparation and the amount of P70. The immature core subparticles isolated from these RLV preparations could themselves be further subdivided into two categories, based on their P70 content and negative stain morphology. Those immature cores containing a high P70/p30 ratio predominantly (85%) exhibited a highly coiled internal structure; those with a relatively low level of P70 exhibited less of an internal coiled structure.

Properties of a P70 proteolytic factor of murine leukemia viruses

Murine leukemia viruses, such as Rauscher leukemia virus (RLV), contain a proteolytic factor which becomes activated after detergent treatment of the virus. This factor specifically cleaves P70, the gag precursor polyprotein which is enriched for in preparations of immature virus core subparticles. The factor has been partially purified on Sephadex G-75 columns. It has a molecular weight of 10,000-12,000 daltons but does not coincide in elution position with the major peaks of the viral polypeptides p10 or p12. Under optimal conditions, that is 2% NP-40 (v/v), 10 mM DTT, (pH 7.2) and incubation for 16 hr at 22 degrees C, cleavage of labeled P70 occurs and increasing amounts of the four gag polypeptides p30, p15, p12 and p10 are obtained. The P70 cleavage activity is blocked by TLCK, TAME, CBZ-lysine and other lysyl-containing protease inhibitors. Further, the CBZ-lysine inhibition is reversible, while an inhibition by phenyl-methylsulfonyl fluoride (PMSF) is irreversible. These inhibition studies suggest that a similarity exists between the P70 proteolytic factor and some serine proteases, such as trypsin. The cleavage pattern of P70-rich immature cores treated with trypsin or chymotrypsin is different from that obtained with the P70 proteolytic factor. Thus murine leukemia virions apparently contain a unique, highly specific protease which is present in small amounts and cleaves P70.

Ultrastructural and histochemical differences in cell surface properties of strain-specific and nonstrain-specific TA3 adenocarcinoma cells

Transmission and scanning electron microscopy and histochemical and biochemical methods were used to investigate differences in cell structure and cell surface properties between the strain-specific TA3-St and nonstrain-specific TA3-Ha ascites sublines of the TA3 murine mammary adenocarcinoma. The TA3-St subline is lethal only to the syngeneic strain A mouse (the strain of origin), whereas the TA3-Ha subline is lethal even to foreign species. In contrast to the TA3-St cell surface, which has numerous folds and irregular microprojections, the TA3-Ha cell has abundant long microvilli of uniform dimensions. An extensive cell surface coat which resembles the "fuzz" coat found on microvilli of normal epithelium was present on the TA3-Ha, but not on the TA3-St cells. After routine fixation, the surface coat of the TA3-Ha cell usually appeared as a filamentous network extending 30-50 nm from the plasmalemma; occasionally, longer filamentous or rod-like structures were found extending 200-400 nm from the plasmalemma. The cell coat material was more extensive on the microvilli than on the intermicrovillous membranes. Free virus-like particles associated with TA3-Ha cells have a similar-appearing surface coat on their outer membranes. The density of surface anionic sites, determined with polycationic ferritin, was greater on the TA3-Ha than on the TA3-St cell surface, consistent with the presence at the TA3-Ha cell surface of several-fold more neuraminidase-susceptible sialic acid groups. The observed surface features of the nonstrain-specific TA3-Ha cell, in comparison to the strain-specific TA3-St cell, are consistent with the suggestion that sialic acid-rich glycoproteins at the TA3-Ha cell surface mask histocompatibility antigens and enhance the ability of malignant cells to invade foreign species.

Rapid purification of an RNA tumor virus and proteins by high-performance steric exclusion chromatography on porous glass bead columns

High-performance steric exclusion chromatography on a 1250-A pore size polyethylene glycol-treated glass bead column was used to purify avian myeloblastosis virus and hamster melanoma virus from plasma protein and tissue culture media. The purified hamster melanoma virus was still infectious and the avian myeloblastosis virus-associated RNA-directed DNA polymerase showed a 1100-fold purification of the virus from one column treatment. Electron microscopy of the purified virus showed intact particles, with surface projections evident. The time required for column purification of the virus was 5 min.