Reduplication of nuclear membranes in HeLa cells infected with adenovirus

A correlative study by electron and light microscopy of the development of type 5 adenovirus. I. Electron microscopy

Stages in the nuclear changes consequent to infection with type 5 adenovirus are shown and described. Viral development seems to be confined to the nucleus where characteristic particles are found. The shape of the intracellular virus depends upon the method of preservation employed, appearing spherical after osmium tetroxide or freezing-substitution, occasionally exhibiting angulated faces after formalin and often assuming an hexagonal profile after potassium permanganate. The non-viral crystals are encountered in zones of low density, and it is suggested that crystallization results from the accumulation of protein in these areas. An hypothesis is presented to explain why these crystals, in contrast to the insect polyhedra, contain few viral particles.

Some dynamic aspects of the nuclear envelope

Nuclei of frog oocytes were isolated, fixed in OsO₄ or KMnO₄, and washed. Nuclear envelopes were then dissected off, placed on grids, and air-dried for electron microscopy. Envelopes from immature oocytes at the stage of beginning yolk deposition were compared with those from mature oocytes. Envelopes from the immature stage had "pores" whose annuli contained more material and showed central globules in the center much more frequently than envelopes from mature eggs. Annuli and central globules had similar appearance and fixation properties, suggesting similar chemical composition. After fixation with KMnO₄, residual densities suggested that "pore" diaphragms are much more variable in thickness or composition in the younger stages. Envelopes of the immature oocytes had about 40 per cent more "pores" per unit area than mature envelopes. In crowding together, the "pores" tended to assume geometrical packing arrays in the young envelope, showing minimum center-to-center spacings of about 1530 A. Since the actual discontinuities in the membranes of the envelope are only about 950 A in diameter, this minimum distance of approach suggests that adjacent formations of the nuclear surface are associated with "pore" structure and perhaps set their limiting spacing distances. If this is true, then it can be deduced that "pore"-associated structures of the nuclear surface are probably circular in outline and about 1500 A in diameter. Isotopically labeled lysine was administered to intact, growing oocytes for 1 to 4 hours and the envelopes were subsequently isolated and fixed. Autoradiography of entire envelopes showed little or no incorporation of lysine into proteins, as compared with small fragments from other parts of the cell of roughly comparable mass. It was concluded that the isolated envelope, as seen in the electron micrographs, does not synthesize or turn over lysine-containing protein at a high rate.

AN ELECTRON MICROSCOPE STUDY OF THE DEVELOPMENT OF A MOUSE HEPATITIS VIRUS IN TISSUE CULTURE CELLS

Samples taken at different intervals of time from suspension cultures of the NCTC 1469 line of mouse liver—derived (ML) cells infected with a mouse hepatitis virus have been studied with the electron microscope. The experiments revealed that the viruses are incorporated into the cells by viropexis within 1 hour after being added to the culture. An increasing number of particles are found later inside dense cytoplasmic corpuscles similar to lysosomes. In the cytoplasm of the cells from the samples taken 7 hours after inoculation, two organized structures generally associated and never seen in the controls are observed: one consists of dense material arranged in a reticular disposition (reticular inclusion); the other is formed by small tubules organized in a complex pattern (tubular body). No evidence has been found concerning their origin. Their significance is discussed. With the progression of the infection a system of membrane-bounded tubules and cisternae is differentiated in the cytoplasm of the ML cells. In the lumen of these tubules or cisternae, which are occupied by a dense material, numerous virus particles are observed. The virus particles which originate in association with the limiting membranes of tubules and cisternae are released into their lumen by a "budding" process. The virus particles are 75 mµ in diameter and possess a nucleoid constituted of dense particles or rods limiting an electron transparent core. The virus limiting membrane is sometimes covered by an outer layer of a dense material. In the cells from the samples taken 14 to 20 hours after inoculation, larger zones of the cell cytoplasm are occupied by inclusion bodies formed by channels or cisternae with their lumens containing numerous virus particles. In the samples taken 20 hours or more after the inoculation numerous cells show evident signs of degeneration.

The zitter rat: membranous abnormality in the Schwann cells of myelinated nerve fibers

Ultrastructural alterations of the Schwann cells were chronologically examined in zitter and in control rats. The membranous abnormalities closely involving the nuclear membranes of the Schwann cells and mesaxons were constantly observed in the zitter rats. These structures consisted of scroll- or whirl-like unit membrane accumulations directly extending to the nuclear envelope. Occasionally, similar membranous structure were observed in association with the endoplasmic reticulum, lysosome or mitochondria in the cytoplasm of the Schwann cells. In the control rats, whirl-like membranous structures in the nuclear membranes of the Schwann cells were observed only intermittently at 1, 5 and at 7 days of age in the developing process. In conclusion, we postulate that the zitter rat, which is an established animal model for hypomyelination of the central nervous system (CNS), has some inherited abnormality related to the membrane biosynthesis and its regulation in Schwann cells as well as in oligodendrocytes.

Characterization of multi-layered membrane generated by rabies virus

Electron microscopy revealed multi-layered membranes within the cytoplasmic inclusion (accumulation of nucleocapsids) produced by rabies virus. When infected BHK cells were maintained at 31 C, an enhancement in production of these membranes occurred in approximately 60% of inclusion-containing cells. Multi-layered membranes were composed of an alternate array of two different layers; an electron-dense, thin membrane and a less dense layer which was thicker. SDS-polyacrylamide gel electrophoresis and immune electron microscopy of isolated multi-layered membrane preparations demonstrated that the structures contained viral G and M2 polypeptides. Our observations suggest that these membranous structures are not a degenerative product of rabies virus infection but rather are related to the replication of viral envelope constituents, although they represent themselves to be an abortive form of viral assembly.

Abnormalities of the nuclear envelope in porcine muscle affected with congenital myofibrillar hypoplasia

The nuclear ultrastructure of muscle fibres in congenital myofibrillar hypoplasia of piglets was studied in order to provide more information on the pathological changes present. In the initial stages of the disease, muscle fibres with a small reduction of myofibrils often had an increased number of nuclear pores. In the more advanced stages of the disease, the following nuclear abnormalities were observed in muscle fibres showing an extensive disintegration of myofibrils: 1) large dilations of the perinuclear cisternae, 2) small nuclear protrusions projecting into these dilations and 3) appositions of stray membranes of the disrupted endoplasmic reticulum to the nuclear envelope. The increase in the number of nuclear pores may be significant in the development of pathological changes in congenital myofibrillar hypoplasia which is thought to be a hereditary disease. The observed abnormalities of the nuclear envelope appear to be characteristic for muscle fibres undergoing degeneration.

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.

Electron microscopy of herpes simplex virus. II. Sequence of development

Examination of infected cells at sequential intervals after infection revealed that the first viral forms to appear were capsids enclosing cores of low density. Not until the 6th hr were dense cores encountered, and at approximately the same time enveloped virus was seen. Envelopment occurred most frequently in close proximity to the nuclear surface, although the process was also encountered within the nuclear matrix and in the cytoplasm. There was often extensive proliferation of the nuclear membrane. Envelopment of the virus by budding from the cell surface was not observed. It was concluded that enveloped virus consitutes the infectious particle and that the unenveloped capsid is unstable outside the cell. Nevertheless, it is likely that capsids enclosing infectious nucleic acid can pass directly from one cell to another after fusion has taken place.

Reduplication of nuclear membranes in tissue-culture cells infected with guinea-pig cytomegalovirus

Images

Electron microscopy of monkey kidney cell cultures infected with rubella virus

Two rubella virus strains isolated in this laboratory were investigated in terms of their growth in LLC-MK(2) cell cultures and their effect on cell morphology. Rubella virus grew readily in LLC-MK(2) cells, but cytopathic effects of the virus were not observed in infected cultures. Such infected cultures can be subcultured indefinitely and continue to shed virus. Examination of rubella-infected cell cultures by electron microscopy showed the presence of annulate lamellae in the cytoplasm of 15% of the cells. No changes were evident in the nuclei. These membranous inclusions varied in complexity from parallel arrays of annulate lamellae to large lamellar structures of complex morphology. An occasional cell contained a crystal lattice structure in association with the lamellae. Larger inclusions, consisting of disorganized arrays of "unit" membranes, were also found. Uninfected cells were devoid of annulate lamellae, crystals, and complex membranous inclusions. No viruslike particles were observed in any part of the cells from infected cultures. The significance of the structures observed has not been determined.