Biomedical subjects

R C Durfee

Publications and source records attributed to R C Durfee.

5 recordsLinked to original sources

PubMed1989

Tomographic reconstruction from energy-filtered images of thick biological sections.

Energy filtration makes it possible to image an approximately 0.5 microm biological section at 80 kV in the electron microscope. Based on spectra taken at different tilt angles, we chose the most probable energy loss, deltaEp +/- 10eV for each tilt angle, as the imaging energy window. A complete tilt series from +60 degrees to -60 degrees at 2.5 degree intervals was collected on the Zeiss EM902 and used in a tomographic reconstruction of transcriptionally active chromatin in the Balbiani ring of Chironomus tentans.

Animals↗

PubMed1987

The varifocal mirror for 3-D display of electron microscope tomography.

Three-dimensional reconstruction by tomographic procedures of objects viewed with transmission electron microscopy generates a volume of densities arrayed in raster format. This volume can be conveniently displayed and analysed employing a varifocal mirror (VFM) and an associated image processing system. We have developed a number of interactive programs useful to display and analyse the 3-D data, including depth windowing, intensity mapping, image zoom, image rotation and cursor overlay. Examples of these functions are presented, employing data from electron microscope tomography (EMT) of a transcriptionally-active eukaryotic gene, the Balbiani ring of Chironomus polytene chromosomes.

Animals↗

PubMed1986

DNA compaction during intense transcription measured by electron microscope tomography.

Thick sections (0.5-1.0 micron) containing pilocarpine-hyperstimulated Balbiani ring (BR) genes of Chironomus tentans salivary glands were reconstructed by electron microscope tomography (EMT). Six transcription loops were analyzed at low resolution permitting a measurement of transcription unit length in situ. Comparison of the average transcription unit length with the BR gene coding region DNA length yields an estimate of the DNA compaction ratio in situ. The estimated DNA compaction ratio (approximately 3-fold) is consistent with a significant degree of nucleosome unfolding in the hyperstimulated BR genes.

Chironomidae↗

PubMed1984

Modeling Balbiani Ring gene transcription with electron microscope tomography.

Cross-sectional views of mature regions of Balbiani Ring (BR) transcription loops were reconstructed by electron microscope tomography. Balsa wood models were built based upon the resulting tomograms. Coordinates of the centers of the ribonucleoprotein BR granules were estimated and employed to calculate the approximate orientation of the BR transcription unit axis in the plastic section. The density of BR granules per micron of transcription unit axis was estimated. Employing structural parameters for mature regions of BR transcription loops derived from present and previous studies, theoretical calculations were performed to examine potential steric restrictions around the central chromatin axis. Tomograms were also observed and photographed on a varifocal (vibrating) mirror to illustrate the utility of a rapid user-interactive 3-D display.

Animals↗

PubMed1983

Electron microscope tomography: transcription in three dimensions.

Three-dimensional reconstruction of an asymmetric biological ultrastructure has been achieved by tomographic analysis of electron micrographs of sections tilted on a goniometer specimen stage. Aligned micrographs could be displayed as red-green three-dimensional movies. The techniques have been applied to portions of in situ transcription units of a Balbiani ring in the polytene chromosomes of the midge Chironomus tentans. Current data suggest a DNA compaction of about 8 to 1 in a transcription unit. Nascent ribonucleoprotein granules display an imperfect sixfold helical arrangement around the chromatin axis.

Animals↗