Biomedical subjects
M J Stallmeyer
Publications and source records attributed to M J Stallmeyer.
Primary cerebral lymphoma.
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Eosinophilic gastroenteritis.
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Substructure of the flagellar basal body of Salmonella typhimurium.
The Salmonella typhimurium basal body, a part of the flagellar rotary motor, consists of four rings (denoted M, S, P and L) and a coaxial rod. Using low-dose electron microscopy and image averaging methods on negatively stained and frozen-hydrated preparations, we examined whole basal body complexes and subcomplexes obtained by dissociation in acid. Dissociation occurs in steps, allowing us to obtain images of substructures lacking the M ring, lacking the M and S rings, and lacking the M and S rings and the proximal portion of the rod. We obtained images of the L and P ring subcomplex. The existence of a subcomplex missing only the M ring suggests either that the S and M rings derive from two different proteins, or that the M ring is a labile domain of a single protein, which makes up both rings. At the 25 to 30 A resolution of our averaged images, the L, P and S rings appear cylindrically symmetric. Images of the M ring show variability that may be due to differences in angular orientation of the grid, but equally could be due to structural variations. Three-dimensional reconstructions of these structures from the averaged images reveal the internal structure and spatial organization of these components.
Quantitative MRI studies for assessment of multiple sclerosis.
Although magnetic resonance imaging (MRI) is a valuable aid in the initial diagnosis of multiple sclerosis (MS), quantitatively MRI has been disappointing in staging and evaluating therapy protocols by means of serial examinations. In this study, image processing algorithms were developed for the global analysis of MR images of the cerebrum. Limited three-dimensional segmentation was achieved through histogram analysis by these algorithms, which are essentially operator independent. The effects of coil response and tip angles, patient positioning, and interslice gap thicknesses were examined for 10 MS patients with repeated examinations for a total of 72 images. Effects of technique and instrumentation errors were approximately 6%, and agreement between two independent operators for measuring the total MR pixel sum from periventricular effusions and intense MS plaques was better than 97% with a standard deviation of 2.9%.
Image reconstruction of the flagellar basal body of Caulobacter crescentus.
The bacterium Caulobacter crescentus has a single polar flagellum, which is present for only a portion of its cell cycle. The flagellum is ejected from the swarmer cell and then synthesized de novo later in the cell cycle. The flagellum is composed of a transmembrane basal body, a hook and a filament. Single-particle averaging and image reconstruction methods were applied to the electron micrographs of negatively stained basal bodies from C. crescentus. These basal bodies have five rings threaded on a rod. The L and P rings are connected by a bridge of material at their outer radii. The E ring is a thin, flat disk. The S ring has a triangular cross section, the sides of the triangle abutting the E ring, the rod and the M ring. The M ring, which is at the inner membrane of the cell, has a different structure depending on the method of preparation. With one method, the M ring makes a snug contact with the S ring and is often capped by an axial button, a new component apparently distinct from the M ring. With the other method, the M ring is similar to that of S. typhimurium; that is, it contacts the S ring only at an outer radius and lacks the button. Averages of the rod-hook-filament subassembly ejected by swarmer cells reveal that the rod consists of two parts with the E ring marking the approximate position of the break. The structures of basal bodies from two mutants defective in the hook assembly were found to be indistinguishable from wild-type basal bodies, suggesting that the assembly of the basal body is independent of the hook or filament assembly.
Image reconstruction of the flagellar basal body of Salmonella typhimurium.
The basal body is thought to be a part of the rotary motor of the bacterial flagellum. It consists of a central rod coaxial with a set of four rings, which are associated with the cell envelope. We used single-particle averaging methods to analyze images of negatively stained basal bodies of Salmonella typhimurium. Several averages were computed, so that the reliability of features could be assessed. We carried out the same analysis on electron micrographs of isolated, negatively stained L-P rings. In order to interpret the averages in terms of a three-dimensional structure, we carried out image reconstruction on them. The resulting three-dimensional map corresponds to the cylindrically averaged structure of the basal body. To show that the reconstruction procedure is legitimate, we demonstrate it on model data. The results of the modelling show that features very near to the axis of the reconstruction are not reliable but that broader, off-axis features are represented faithfully. The L ring is L-shaped, with the long arm of the L parallel to the axis of the rod, and the short arm pointing away from the rod. The P ring, on the other hand, appears to be a ring or disk. The position of the L-P ring complex on the rod seems to vary somewhat, consistent with its putative role as a bushing. The cross-sectional shape of the S ring is that of a frustum rather than a disk. The M ring, which is oval in cross section, sits atop the S ring, making contact with it at an outer radius. The S ring appears to make contact with the rod, whereas the M ring does not. This situation, if true, is difficult to reconcile with the common notion that the S ring is stationary and the M ring rotates. It seems more likely that the S ring and rod rotate as a unit.