Improved technique for electron microscopy of cultured cells.

A number of techniques are presented which precise selection and efficient preparation of individual cultured cells for electron microscopy. Techniques described include marking of the living and embedded cells, drilling and mounting cores of embedded material, and improved technique for marking of the selected area on the block face before trimming.     

Electron microscopy of antibody-labelled cells of Streptococcus mutans.

Examination of immune complexes between cells of Streptococcus mutans and homologous antiserum by the techniques of thin-sectioning and freeze-etching revealed that the cells were embedded within and extensive matrix 80-90 nm thick with defined boundaries.     

Group selection, individual selection, and the evolution of genetic drift.

In a subdivided population, genetic drift affects variation between groups, and thus it can have an important effect on the outcome of evolution (Wright, 1978). The rate of genetic drift is determined, in part, by the behaviour of population members. This paper presents three mathematical models in which behavioural traits that affect the rate of genetic drift are allowed to coevolve with traits that are under selection at the group and individual levels. The results show that if group selection is strong relative to individual selection, then behavioural traits that enhance the rate of genetic drift will tend to increase in frequency. The strength of this effect depends, in part, on the way in which vacant sites are colonized.     

Electron microscopy for the diagnosis of tumours.

The role of leukocyte transfusions in the prevention and treatment of infections in adults with granulocytopenia was investigated. Leukocytes were obtained from healthy volunteers by continuous-flow centrifugation. Histocompatibility antigen (HLA)-matched leukocytes were used to assess the prophylactic value of leukocyte transfusions. Seven patients with acute myelogenous leukemia received HLA-matched leukocytes during the period of maximal granulocytopenia associated with initial remission induction therapy; 20 concurrently treated patients who did not receive leukocyte transfusions were the control group. The patients receiving HLA-matched leukocytes had significantly fewer (P = 0.043) infectious episodes (not bacteriologically proven) during the study period, and remission occurred in 5 of the 7, compared with 10 of the 20 controls. In addition, 52 series of two or more ABO-compatible transfusions were given to 50 patients with proven infection or elevated temperature presumed due to infection and a granulocyte count of less than 0.5 X 10(9)/L. Response, indicated by a decrease in temperature, occurred in 23 patients. Leukocyte transfusions thus have an important adjuvant role in the management of patients with severe granulocytopenia.     

Electron microscopy: essentials for viral structure, morphogenesis and rapid diagnosis

Electron microscopy(EM) should be used in the front line for detection of agents in emergencies and bioterrorism,on accounts of its speed and accuracy.However,the number of EM diagnostic laboratories has decreased considerably and an increasing number of people encounter difficulties with EM results.Therefore,the research on viral structure and morphology has become important in EM diagnostic practice.EM has several technological advantages,and should be a fundamental tool in clinical diagnosis of viruses,particularly when agents are unknown or unsuspected.In this article,we review the historical contribution of EM to virology,and its use in virus differentiation,localization of specific virus antigens,virus-cell interaction,and viral morphogenesis.It is essential that EM investigations are based on clinical and comprehensive pathogenesis data from light or confocal microscopy.Furthermore,avoidance of artifacts or false results is necessary to exploit fully the advantages while minimizing its limitations.     

Graded differential photoreceptor orientation: ramifications for ultramicrotomy of retina.

When sectioning small blocks of tissue from the retina of the eye, it is sometimes difficult to obtain sections which simultaneously cut squarely across the inner retinal layers and are on the long axis of the photoreceptors. This difficulty is, at least partially, due to the fact that the receptors tilt progressively relative to the tangent to the retinal curve at progressively more peripheral loci. Consideration of the graded differential orientation of the receptors indicates that, in order for the section to be simultaneously coaxial with the receptors and the inner retinal layers, the plane of the section must be parallel to and include the anterior-posterior axis of the eye, as is the case when the whole eye is sectioned through its center. It is illustrated that this criterion can be met for small blocks of retina if the block is excised along a parallel of the eye and the plane of section is perpendicular to the tangent to the retinal curve and the parallel. An approach which accomplishes this is described. Theoretical analysis suggests that distortion of apparent size of structures in the retina can become significant within a few degrees of the posterior pole if this condition is not met.     

Electron microscopy of frozen-hydrated bacteria.

Amorphous, unstained, frozen-hydrated sections of bacteria provide a faithful high-resolution image of procaryotic cells. Conventional preparation artifacts due to fixation, staining, and dehydration are nonexistent. Freezing damage is avoided by using glucose as a cryoprotectant. Cutting damage on frozen material is severe, but sectioning artifacts, being always related to the cutting direction, can be systematically recognized and thus taken into consideration. Geometry and density distribution of the bacterial envelope can be resolved to about 3 nm. The following main features have been observed. In Escherichia coli the inner and outer membranes have an approximately uniform density profile. The distance between the two membranes is constant, ca. 33 nm. In Staphylococcus aureus the cell wall is ca. 40 nm wide. It is bordered on the cytoplasmic side by an asymmetric 5.5-nm-wide bilayer. The bacterial nucleoid, clearly visible with conventional preparation methods, appears in exponentially growing bacteria as an ill-defined central region with approximately the same density as the rest of the cytoplasm. It becomes more clearly visible when bacteria are in the stationary phase, plasmolysed, fixed, or stained. We confirm that "mesosomes," hitherto quite often considered to be essential organelles in all procaryotes, are artifacts. They appear in large numbers during osmium fixation.     

The killer phenomenon in Ustilago: Electron microscopy of the dsRNA encapsidated in individual virus particles

From earlier studies with the Ustilago maydis virus and other dsRNA viruses it is known that discrete dsRNA segments typical of each virus are obtained by extraction. A variation exists with respect to the encapsidation of these segments among different viruses. The encapsidation of the genome in individual particles of the Ustilago virus was examined by electron microscopy after disruption of virus particles. The study included the P6 wild-type and 2 mutants containing only part of the genome. The results indicate that most virus particles of the wild-type and the mutants contain up to 12–14×10⁶ daltons of dsRNA. Since the largest extracted molecule is 3.2×10⁶D these findings suggest that an individual particle may contain more than one segment of dsRNA. Free linear molecules that exceed in size the extracted segments were also found following the disruption of each of the 3 virus types examined. Thus, the viral genome seen segmented after extraction is organized as a concatamer in the capsid and each virus particle can contain an entire viral genome consisting of each type of the segments seen after extraction, a repeat of a single segment or a random assortment. In each case the information may be organized as a concatamer.