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Biomedical subjects

G F Bahr

Publications and source records attributed to G F Bahr.

At least 19 recordsLinked to original sources
PubMed1990

Mass and molecular weight of isolated nuclear rings.

Nuclear rings are cell structures found at the nuclear cortex wedged between the nuclear envelope and the chromatin fiber network. In previous publications we have dealt with their morphology, relationships with the nuclear membranes, chromatin fibers and cytoskeletal filaments; and more recently, with their measurements at high electron microscope resolution. In this article we have calculated the mass and molecular weight of 336 isolated nuclear rings from human circulating lymphocytes using a photometric procedure and polystyrene latex spheres as the standard for weight calibration. Our results show a range of mass of 0.4-35.5 x 10(-16) g (equivalent to 0.2-21.2 x 10(8) Da with a positively skewed distribution (median: 3.3 x 10(-16) g or 2.0 x 10(8) Da). Mass and volume of nuclear rings were highly correlated. In addition, it was possible to calculate the area, the whole mass and the mass per unit area of the nuclear envelope present in the center of the nuclear rings. The mass of this area also shows a lognormal distribution (median of mass/unit area: 37.3 x 10(-8) pg/nm2 or 1.9 x 10(5) Da/nm2). We discuss the significance of this results as parameters for the characterization of the nuclear rings and their possible implications for a new interpretation of nuclear cortex architecture, nucleocytoplasmic traffic and macromolecule segregation between the two main cell compartments.

Calibration↗
PubMed1988

A comparative morphometric and cytophotometric study of intraductal hyperplasia and intraductal carcinoma of the breast.

The Feulgen DNA content and the nuclear measurements of four groups of intraductal proliferations of the breast (hyperplasia, atypical hyperplasia, well-differentiated carcinoma without cytologic atypia and intraductal carcinoma with cytologic atypia) were compared. Intraductal carcinoma with atypia was the only group distinct from the others on the basis of DNA content, nuclear area and perimeter. Although the other groups were separable from intraductal carcinoma with atypia, they could not be reliably distinguished from each other by any combination of measurements. At best, 69% of well-differentiated intraductal carcinomas could be distinguished from atypical hyperplasias using a combination of DNA content and nuclear perimeter measurements. Thus, the difficult distinction of atypical hyperplasia from well-differentiated intraductal carcinoma by light microscopy was not aided by DNA analysis or by nuclear measurements.

Breast↗
PubMed1988

Cytophotometric determination of DNA in mesotheliomas and reactive mesothelial cells.

Cytophotometry was used to study the nuclear DNA content of cells in Feulgen-stained effusion specimens from 18 patients with mesothelioma and 14 patients with reactive mesothelial proliferations. The mean DNA content (MDNA) of mesothelioma cells was significantly higher than that of reactive mesothelial cells (P less than .001). Other parameters reflecting the DNA content also differed significantly between the two kinds of cells, including (1) the ratio of mean mesothelial DNA to mean lymphocyte DNA, (2) the percentage of mesothelial cells with DNA content exceeding three times the lymphocyte MDNA and (3) the coefficient of variation of the DNA content. Since these parameters were highly correlated, only one was accepted in a stepwise linear discriminant model for distinguishing reactive from mesotheliomatous effusions. The model correctly classified all of the reactive effusions studied and 89% of the mesotheliomatous effusions. These results indicate that DNA analysis, using the Feulgen stain and cytophotometry, yields criteria that may be useful in distinguishing benign reactive mesothelial cells from malignant mesothelioma in effusions when used in conjunction with other traditional parameters.

Adult↗
PubMed1987

Three-dimensional reconstruction of a human metaphase chromosome from electron micrographs.

A complete human metaphase chromosome has been reconstructed from a series of electron microscopical projections obtained by tilting the specimen stage at 3 degree intervals from -60 to +60 degrees. The reconstructed structure is about 3.0 microns long, 1.6 micron wide, and 0.8 micron thick. The mass distribution was fairly homogeneous within the chromatids and neither a hollow nor a dense core was observed. The distribution and course of fibers observed are most consistent with a looping model of chromosome structure.

Algorithms↗
PubMed1987

Morphometry and cytophotometric assessment of DNA in smooth-muscle tumors (leiomyomas and leiomyosarcomas) of the gastrointestinal tract.

The difficulties in predicting the biologic behavior of gastrointestinal (GI) smooth-muscle tumors (leiomyomas and leiomyosarcomas) based on the usual criteria of malignancy are discussed. In order to evaluate the prognostic importance of the nuclear DNA content and nuclear dimensions, measurements were performed on Feulgen-stained sections of GI smooth-muscle tumors from 66 patients. The best discrimination between benign and malignant tumors was obtained by using DNA index and tumor size as descriptors in a linear discriminate analysis. This method separated 79% of the benign and 97% of the malignant smooth-muscle tumors. However, as with conventional criteria for malignancy, there remained a group of tumors close to the discriminating line with an indeterminate malignant potential. In an attempt to reduce the number of such indeterminate tumors, future studies will include the use of several descriptors in a multivariate analysis system and the application of flow cytometric studies to all tumors.

Adolescent↗
PubMed1987

Mass, volume and dimensional distributions in biology, with special reference to cells.

The positively skewed distribution of mass (weight) in biology was examined, and it was concluded all weight or masses can best be described by lognormal theory. Examples are given ranging in weight from viruses to humans. The accretion of mass proceeds as "more of the same" and primarily does not alter function. Immunologic properties must be carefully preserved. Small biologic entities can afford only small mass gains or losses while preserving their functionality; the larger the entity, the larger is the variability of mass functionally permitted. A well-established, convenient graphic method of analyzing a sample is described, with the advantages and pitfalls discussed. At the cellular level, volume and dimensions are lognormally distributed whenever the specific gravity (g/cu cm) is nearly homogenous among the particles or cells. In multicellular organisms, dimensions and forms (such as height and cranial circumference) are primarily the product of multifactorial genetic determinants and frequently appear as normal distributions. This paper discusses the meaning of the law of proportionate effects for small biologic objects, especially cells, and how an initial or "elementary" distribution may be conceived.

Animals↗
PubMed1987

Morphometry of nuclear rings at high electron microscopic resolution.

In studying the fine structure of the nuclear chromatin, a new organelle was discovered, the nuclear ring. In its isolated form, this structure is rather like a geometric torus: a smooth, structureless ring. This paper presents the results of electron microscopic morphologic measurements on 424 isolated rings, i.e., rings found free of any fibrous connections. From the measurements of inner and outer diameters, other geometric features were also calculated. Overall, the size of the rings varied about fivefold. Inner and outer diameters were closely correlated, suggesting a rather stable thickness of the ring itself. The significance of the nuclear ring is as yet poorly understood. With its occasionally intimate connections to both chromatin fibers and to the inside of the inner nuclear envelope, its role is likely to be a crucial one. The membrane covering its opening is none other than the bilayer of the nuclear envelope. The concept of a patent opening or "pore" does not appear tenable in the face of this and related findings.

Chromatin↗
PubMed1986

A chromosome's protein is a dependent variable of the total metaphase protein.

Chinese hamster metaphases were stained with dansyl chloride to determine protein. Using a microfluorometer, the fluorescence of chromosome number one and the total of the fluorescence of the metaphase were measured. The two measurements were found to be correlated with a coefficient of 0.640, suggesting that protein content in a single chromosome is a dependent variable of the protein content of the respective metaphase.

Cell Line↗
PubMed1985

Some practical considerations in quantitative absorbance microspectrophotometry. Preparation techniques in DNA cytophotometry.

An experimental review of the Feulgen and gallocyanine-chrome-alum stains for quantitative cytophotometry of DNA in tissue sections yielded information on the preparation and staining of tissue for quantitative absorbance microspectrophotometry. (1) Tissues routinely fixed in formalin are suitable for either stain. Specimens fixed with glutaraldehyde-containing fixatives are not satisfactory for Feulgen staining, nor are ethanol-fixed specimens, unless they are post-fixed in formalin. (2) The pararosaniline dyes, used in the Feulgen stain, are sufficiently pure to use if a solution of the dye in ethanol shows an absorbance peak at 543 to 546 nm. (3) The Feulgen stain provides good reproducibility when the staining solution is adjusted to pH 1.5. (4) Gallocyanine is the best stain to use on Bouin-fixed or glutaraldehyde-fixed tissues. (5) Where fixation is an option, Carnoy and methanol-formalin-glacial acetic acid are excellent fixatives that can be followed by either stain. (6) Selection of the thickness of a tissue section involves a compromise. Requirements of minimum nuclear overlap and sharp focusing favor a section thickness of 4 micron to 6 micron. On the other hand, the requirement for full nuclear thickness, as judged by absorbance equivalent to that of a touch preparation, demands sections as thick as 8 micron in the case of mouse liver. Within this range, the optimum thickness, therefore, is determined by the particular tissue, the range of its nuclear sizes and its packing density. (7) The refractive index of the mounting medium should be closely matched to that of the background structure of the tissue sections. For animal tissues, we found that media with refractive indices of 1.54 to 1.56 are suitable.

Animals↗
PubMed1985

The distribution of nuclear mass, volume and dimensions.

Our own measurements and a review of measurements presented in the literature showed that the mass, volume and dimensions of cell nuclei are distributed with a skew towards higher values, a distribution that can best be described as lognormal. The practical consequences of this finding suggest that the measurements of mass and of size should be plotted on a logarithmic scale while DNA values are appropriately presented on a linear scale. The distribution of DNA values of normal cells represents errors introduced by random disturbances in preparations and measurements.

Animals↗
PubMed1981

Observations on the structure of mechanically stretched chromatin fibrils.

During the spreading of human chromosomes prepared from cultured human lymphocytes, the peripheral fibers attaching the chromosome to the support film are mechanically stretched. The stretching reveals structural elements of the fibers; some of these features have been described earlier, for extracted chromatin. The molecule of DNA is bared through stretching and binds labeled actinomycin D in consequence. One of the prominent features of stretched fibers is the irregularity of resulting structures. This paper further demonstrates the excellent resolution obtainable by electron impact evaporation of tungsten.

Chromatin↗
PubMed1979

Reconstruction of a chromosome model from its projections.

As a pilot experiment towards the reconstruction of human chromosomes from their electron microscopic projections, a chromosome model was photographed and several cross-sectional planes successfully reconstructed. Some practical constraints and conditions for this type of work are defined.

Chromatin↗
PubMed1977

Association of centrioles and chromosomes observed in preparations of whole-mounted human chromosomes.

Pairs of centrioles are a frequent finding in whole-mounted, critical-point-dried chromosome preparations from normal and irradiated human lymphocyte cultures. Most frequently they are found in association with a group C chromosome, although apparently free diplosomes are not uncommon. Fibers that in every respect are the morphologic equivalent of those seen in the body of the chromatid connect to the thick-walled open-ended part of the parent centriole. These features argue for the possibility that fibers connecting centrioles are an integral part of nuclear or chromosomal chromatin. It was observed that the smaller (daughter) centriole was connected and held in the well-known angular configuration to the thick-walled opne end of the parent centriole by a few, probably only two, colchine-resistant fibers.

Chromatids↗
PubMed1977

Electron microscopy of negatively stained jackbean urease at three levels of quaternary structure, and comparison with hydrodynamic studies.

Electron microscopy, with sodium phosphotungstate as negative stain, has been carried out on purified jackbean urease prepared at three levels of quaternary structure: (a) A1 urease, Mr = 240 000, S20,W = 11.5 S (b) alpha urease, Mr = 480 000, S20,w = 18.3 S (c) polymers of alpha urease above the tetramer stage. The compatibility of the images from level to level leaves no doubt that the enzyme itself is being visualized, and the following geometry is suggested by electron microscopy: A1 molecules are cyclic trimers, which pair up in eclipsed position across a 1-nm cleft to form the hexameric alpha, which displays D3 (or 32) symmetry of a trigonal prism. Polymers consist of alpha molecules aligned with their clefts coplanar and an angle of 120 degrees between each triplet of 3-fold axes. These features correspond reasonably well with sedimentation and electrophoretic studies of the solvated enzyme, which have indicated a hemispherical A1, a spherical alpha, and string-of-beads polymers. Sedimentation constants of the urease polymers up through the pentamer level were found to be compatible with the rosette, straight-chain, and zig-zag forms seen in the electron microscope, and with the suggested protomer arrangement in A1 and alpha urease.

Macromolecular Substances↗
PubMed1976

Determination of the mass of viruses by quantitative electron microscopy.

The photometric method of quantitative determination of dry mass by electron microscopy has been applied to the study of various types of viruses: animal, plant, insect, and bacterial. The method is applicable to all viruses having a mass of 1 x 10-18g or greater. The molecular weight of viruses can be calculated from the mass value by multiplying it by Avogadro's number. In comparison to other methods of determining the molecular weight of viruses, sedimentation and diffusion, sedimentation equilibrium, light scattering, and electron microscopy counting, the method of quantitative electron microscopy is competitive. In some ways quantitative electron microscopy is superior to other methods for the determination of molecular weight: There is no limitation to the size of the virus, no experimental time involved and no concentration and purity of virus preparations required, and finally it is independent of the geometry of the virion. In one important aspect it is unique when compared to other methods; namely, it affords one the capacity to analyse individual virus particles.

Biophysical Phenomena↗
PubMed1975

Comparison of G-, Q- and EM-banding patterns exhibited by the chromosome complement of the Indian muntjac, Muntiacus muntjak, with reference to nuclear DNA content and chromatin ultrastructure.

When the chromosomes of the Indian muntjac, Muntiacus muntjak, were compared following treatment with two presently used banding methods, trypsin-Giemsa (G) and quinacrine-hydrochloride (Q) with structural bands as seen in the electron microscope, definite correlations were observed with respect to the numbers and positions of individual bands. - Weights obtained for the individual chromosomes were: No. 1, 9.98 pg; No. 2, 4.10 pg; No. 3, 4.43 pg; No. 3-X, 5.05 pg; and Y, 0.55 pg. Average diameters and weights for individual fibers were 193 A and 8.74 times 10-16 g/micron, respectively, for stimulated metaphase chromosomes and 185 A and 8.73 times 10-16 g/micron, respectively, for unstimulated chromosomes. Fibers of interphase nuclei exhibited an average diameter of 191 A and a weight of 5.87 times 10-16 g/micron. - The total amound of nuclear DNA present in interphase nuclei was 3.88 pg.

Animals↗