An electron microscope for the aberration-corrected era.

Improved resolution made possible by aberration correction has greatly increased the demands on the performance of all parts of high-end electron microscopes. In order to meet these demands, we have designed and built an entirely new scanning transmission electron microscope (STEM). The microscope includes a flexible illumination system that allows the properties of its probe to be changed on-the-fly, a third-generation aberration corrector which corrects all geometric aberrations up to fifth order, an ultra-responsive yet stable five-axis sample stage, and a flexible configuration of optimized detectors. The microscope features many innovations, such as a modular column assembled from building blocks that can be stacked in almost any order, in situ storage and cleaning facilities for up to five samples, computer-controlled loading of samples into the column, and self-diagnosing electronics. The microscope construction is described, and examples of its capabilities are shown.

Improvements in the X-ray analytical capabilities of a scanning transmission electron microscope by spherical-aberration correction.

A Nion spherical-aberration (Cs) corrector was recently installed on Lehigh University's 300-keV cold field-emission gun (FEG) Vacuum Generators HB 603 dedicated scanning transmission electron microscope (STEM), optimized for X-ray analysis of thin specimens. In this article, the impact of the Cs-corrector on X-ray analysis is theoretically evaluated, in terms of expected improvements in spatial resolution and analytical sensitivity, and the calculations are compared with initial experimental results. Finally, the possibilities of atomic-column X-ray analysis in a Cs-corrected STEM are discussed.

Characterisation of two novel fork-head gene homologues of Schizosaccharomyces pombe: their involvement in cell cycle and sexual differentiation.

The fork-head type transcription factors are a class of regulators that function in a broad spectrum of cellular and developmental processes in many species ranging from yeasts to human. Previous data on yeast fork-head genes suggested roles for these regulators in the control of cell division, sexual differentiation and development. The genome of Schizosaccharomyces pombe has four genes that code for proteins containing fork-head domains (FKH), two of which have been characterised. Here we describe the remaining two genes, fhl1 and fkh2, that code for proteins containing fork-head-associated domains (FHA) besides their FKHs. Neither of them is essential for viability, although the deletion of either fhl1 (putative homologue of Saccharomyces cerevisiae FHL1) or fkh2 (similar to FKH1 and FKH2 of S. cerevisiae) reduced the growth rate and caused an extension of cell length due to delayed G2-to-M transition. Occasionally, multiseptate cells were also produced, indicating the involvement of fhl1 and fkh2 in efficient septum cleavage. The fkh2Delta cells were slightly more sensitive than the wild-type cells to certain environmental stresses, showed reduced fertility and occasional deficiencies in meiosis II, indicating that fkh2 might also act in stress response and sexual differentiation.

Direct sub-angstrom imaging of a crystal lattice.

Despite the use of electrons with wavelengths of just a few picometers, spatial resolution in a transmission electron microscope (TEM) has been limited by spherical aberration to typically around 0.15 nanometer. Individual atomic columns in a crystalline lattice can therefore only be imaged for a few low-order orientations, limiting the range of defects that can be imaged at atomic resolution. The recent development of spherical aberration correctors for transmission electron microscopy allows this limit to be overcome. We present direct images from an aberration-corrected scanning TEM that resolve a lattice in which the atomic columns are separated by less than 0.1 nanometer.

Towards sub-0.5 A electron beams.

In the 4 years since the previous meeting in the SALSA series, aberration correction has progressed from a promising concept to a powerful research tool. We summarize the factors that have enabled 100-120kV scanning transmission electron microscopes to achieve sub-A resolution, and to increase the current available in an atom-sized probe by a factor of 10 and more. Once C(s) is corrected, fifth-order spherical aberration (C(5)) and chromatic aberration (C(c)) pose new limits on resolution. We describe a quadrupole/octupole corrector of a new design, which will correct all fifth-order aberrations while introducing less than 0.2mm of additional C(c). Coupled to an optimized STEM column, the new corrector promises to lead to routine sub-A electron probes at 100kV, and to sub-0.5A probes at higher operating voltages.

The Schizosaccharomyces pombe genes sep10 and sep11 encode putative general transcriptional regulators involved in multiple cellular processes.

We have previously described the genetic analysis of eleven complementation groups ( sep6- sep16) defined by Schizosaccharomyces pombe mutants that are defective in cell separation and sexual differentiation. Here we report on the cloning and characterisation of two members of this set, sep10 and sep11. Sequencing of the full-length sep10 revealed a continuous ORF that encodes a conserved protein with possible functions in general transcriptional regulation. The coding region of sep11 is interrupted by introns and the putative s ep11 protein shows no sequence similarity with known proteins of other species. Disruption of each gene causes temperature sensitivity. Simultaneous disruption of both genes is lethal, demonstrating that sep10 and sep11 perform related, overlapping functions. Overexpression of aff1/ste11, a pivotal regulator of sexual development, suppresses the sterility of sep10 (-) cells, which suggests that sep10 is needed for the activity of aff1/ste11.

Marker construction and cloning of a cut1-like sequence with ARS activity in the fission yeast Schizosaccharomyces japonicus.

The dimorphic fission yeast Schizosaccharomyces japonicus has proved to be an excellent experimental model for the investigation of the eukaryotic cell. Here we show that it has a haplontic life cycle, in which the diploid phase is confined to the zygote. To make it amenable to genetic and molecular analysis, we generated genetic markers and cloned a genomic sequence which acts as ars when integrated into a plasmid. Diploids suitable for testing complementation and recombination between markers can be formed by protoplast fusion. The complementation tests and the recombination frequencies determined in octads of spores identified 28 non-allelic groups (genes) of mutations of the auxotrophic and mycelium-negative mutants. Two groups of linked markers were also identified. The cloned fragment, which expresses ars activity, encodes a putative amino acid sequence highly similar to a conserved domain of proteins Cut1 (Schizosaccharomyces pombe), BimB (Aspergillus nidulans) and Esp1 (Saccharomyces cerevisiae).

Molecular dynamics simulation of metallothionein-drug complexes.

The intermolecular interactions of metallothionein with nitrogen mustard drugs were studied by molecular dynamics simulations. Previous laboratory experiments have defined selective alkylation of two cysteine residues, and selective binding was proposed to precede alkylation. The present study provides information about accessibility to cysteines based on evaluating the intermolecular energies and distances in the first few ps of dynamics simulations. A series of dynamics simulations was performed with three drug molecules positioned at the eight most solvent accessible cysteine residues of the dimeric form of the protein. Sites proximal to the sulfhydryl groups of Cys-33 and Cys-48 were found to be the most favorable for complexing the aziridinium forms of chlorambucil, melphalan, and mechlorethamine. The sites for preferential binding are in qualitative agreement with the sites of selective alkylation defined experimentally.

Proteinase inhibitors from desert locust, Schistocerca gregaria: engineering of both P(1) and P(1)' residues converts a potent chymotrypsin inhibitor to a potent trypsin inhibitor.

Two peptides, SGCI and SGTI, that inhibited chymotrypsin and trypsin, respectively, were isolated from the haemolymph of Schistocerca gregaria. Their primary structures were found to be identical with SGP-2 and SGP-1, two of a series of peptides isolated from ovaries of the same species (A. Hamdaoui et al., FEBS Lett. 422 (1998) 74-78). All these peptides are composed of 35-36 amino acid residues and contain three homologous disulfide bridges. The residues imparting specificity to SGCI and SGTI were identified as Leu-30 and Arg-29, respectively. The peptides were synthesised by solid-phase peptide synthesis, and the synthetic ones displayed the same inhibition as the natural forms: SGCI is a strong inhibitor of chymotrypsin (K(i) = 6.2 x 10(-12) M), and SGTI is a rather weak inhibitor of trypsin (K(i) = 2.1 x 10(-7) M). The replacement of P(1) then P(1)' residues of SGCI with trypsin-specific residues increased affinity towards trypsin 3600- and 1100-fold, respectively, thus SGCI was converted to a strong trypsin inhibitor (K(i) = 5.0 x 10(-12) M) that retained some inhibitory affinity towards chymotrypsin (K(i) = 3.5 x 10(-8) M). The documented role of both P(1) and P(1)' highlights the importance of S(1)'P(1)' interactions in enzyme-inhibitor complexes.

Eleven novel sep genes of Schizosaccharomyces pombe required for efficient cell separation and sexual differentiation.

Genetic analysis of 20 sterile mutants prone to form hyphae revealed 11 novel ste genes (sep6 to sep16) of Schizosaccharomyces pombe. None of the mutants was completely mycelial. Most mutants formed branching hyphae and showed normal septation. Aberrant septal structures and actin distribution were seen only at 36 degrees C. sep9-307, sep14-576 and sep15-598 showed genetic interactions with sep1-1, a mutation in a forkhead transcription factor homologue. Additional genetic interactions were detected between sep6-194, sep15-598 and cdc16-116, a mutant allele of an anaphase modulator of p34cdc2. sep9-307 and sep15-598 caused dikaryosis in wee1- background. In mating and sporulation tests, sep6-, sep7-, sep9-, sep10-, sep11- and sep15- proved to be defective in conjugation only, whereas sep8-, sep13- and sep16- were also defective in meiosis-sporulation. sep12- and sep14- were only partially sterile. All mutants could produce M-factor but sep8-, sep11-, sep15- and sep16- were defective in P-factor production. The mutations in sep8, sep11 and sep16 suppressed the pat1-114-driven meiosis. All mutants were sensitive to the presence of higher concentrations of chloride in the medium and to short heat shocks. The diversity of the mutant phenotypes and the pleiotropic effects of the mutations suggest that these sep genes might act in, or interact with, a multiple overlapping network of regulatory modules.

Genetics, physiology and cytology of yeast-mycelial dimorphism in fission yeasts.

The order Schizosaccharomycetales contains a dimorphic and two yeast species. Sch. japonicus can form both yeast cells and mycelium, depending on the substrate and the culturing conditions. Sch. pombe is a strictly unicellular organism, but it can be forced to form mycelial cell chains by inactivating members of the sep gene family. The mutations in most of the sep genes confer pleitropic phenotypes indicating functional involvement in MAP-kinase-mediated signalling pathways. Two of them were found to encode transcription factor homologues of other eukaryotes.

[Mandibular fracture in an infant]. / Csecsemökorú gyermek állkapocstörése.

Maxillofacial fractures under 10 years of age are uncommon, with an occurrence of 7.3%. Isolated fractures of the mandible are even more rare, due to the fact that in young children the mandible is relatively small and resilient. Some authors suggest that the occurrence of this form of fracture is about 1-5%. Different methods have been described for treatment of fractures off the mandible in children. In the therapy since the introduction of titanium mini plates the trend has been to select surgical repositioning followed by osteosynthesis. This paper describes the management of a 7-month old boy with isolated mandibular fracture, using this method to avoid the damage of the tooth germs. This particular case raises the issue of child abuse, which is on the increase in Hungary as well. To find a kind of solution would be not only a task of dentists but also of society in general.

Quantitative optical tomography of chemical waves and their organizing centers.

Interference from topological, chemical and biological analogies led to the guess that a wide variety of homogeneous three-dimensional materials characterized by "excitability" might support persistent particle-like "organizing centers." These are vortex filaments, typically rings, around which excitation fronts circulate in the uniform medium. Robust organizing centers were recently discovered numerically in several cases, motivating a search for them in nature. But if a candidate were observed there would still be no way to examine it for the expected topological intricacies. To solve this problem we designed and constructed a hybrid chemical/optical/computational instrument using the familiar principles of tomography by filtered backprojection. We demonstrate here that it can quantitatively resolve chemical vortex filaments in a new excitable medium fashioned for the purpose. The next step, not described here, is to use the light sensitivity of this medium to contrive initial conditions from which topologically exotic organizing centers would arise and possibly persist. (c) 1996 American Institute of Physics.

[Computer tomography in implantology]. / Komputertomográfiás vizsgálat az implantológiai diagnosztikában.

During the planning of implantation the CT method helps in determining the location of the implant and aids in choosing the right implant. It provides the following measurable information about the jaw-bones: height and width; exact location of bone deficiencies; the orovestibular shape of the alveolar process; the course of the mandibular canal; the location of the mental foramen; the location and size of the canalis incisivus; the area of the nasal cavity and the maxillary sinus; the quality of the bones and the relationship between cortical and spongious bone. In comparison to the X-ray examinations possession of these informations increase significantly the safety of planning before surgery.

[Correlation between meteorologic factors and periostitis of dental origin in Debrecen]. / Idöjárási jelenségek és dentális eredetü periostitisek összefüggéseinek vizsgálata Debrecenben.

Correlation between bioclimatical and meteorological factors is well documented. The aim of this study was to investigate the correlation between dental periostitis and meteorological fronts, cyclon and anticyclon. We found a positive, statistically significant correlation between occurrence of warm meteorological front, cyclon, anticyclon and prevalence of dental periostitis. It could have important implications in organizing the work of dental teams.

The role of reactive oxygen intermediates in the pathogenesis of chronic apical periodontitis.

The level of malondialdehyde, a stable end product of lipid peroxidation induced by reactive oxygen intermediates and the activity of two potent antioxidant enzymes, superoxide dismutase and glutathione peroxidase, was investigated in tissue homogenates of 22 surgical periapical granuloma specimens. Malondialdehyde levels were significantly higher and glutathione peroxidase activity was significantly lower in periapical granuloma samples than in healthy gingival tissue homogenates, which were used as controls. The activity of superoxide dismutase was similar in periapical granuloma and in control samples. Our results indicate an altered balance between the production and the elimination of toxic oxygen metabolites in chronic apical periodontitis. We hypothesize that reactive oxygen intermediates, which are being produced by activated phagocytic cells abundantly present in periapical granulomas, can contribute to periapical tissue injury and bone loss in this disease.

[Free-end reconstruction by dento-osseous autotransplantation]. / Sorvégi hiány pótlása dentoossealis autotransplantatum segítségével.

The authors describe an endosseal autotransplantation A tooth is extracted together with its parodontium and the surrounding bone. It is implanted into a different place where the bone had been prepared. Upper left unilateral free-end saddle cases were solved by removing the tooth No 24 into the place of No 27. A bridge was constructed after 6 weeks using the 23 as abutment. The metal-ceramic bridges have been used by the patients for 3 years without complaint.

Two-dimensional echocardiographically guided pericardiocentesis in a horse with traumatic pericarditis.

Two-dimensional echocardiographic (2DE) examination was performed on a horse with clinical signs of pericardial effusion. Thickening of the pericardium, excess amount of pericardial fluid, elevation of the cardiac apex, and right ventricular compression, characteristic of cardiac tamponade, could be seen on 2DE recordings. Fibrinous pericarditis was suspected by observation of fibrinous strands in the pericardial fluid and epicardial fibrin deposits. Echocardiographically guided pericardiocentesis was performed, and 4 L of fluid was removed from the pericardial sac. Streptococcus zooepidemicus was isolated from the fluid. Pericardiocentesis was repeated for 3 days, and medication was administered. Despite temporary improvement in cardiac function, the horse's condition deteriorated gradually, and euthanasia was performed on the ninth day of hospitalization. Necropsy revealed chronic serofibrinous pericarditis of traumatic origin, attributable to an intercostal stab wound entering the pericardium and the apical portion of the myocardium.