Marked Strain Research Articles

Bcr-abl, the hallmark of chronic myeloid leukaemia in man, induces multiple haemopoietic neoplasms in mice.

The chromosome translocation forming the hybrid bcr-abl gene is thought to be the initiating event in chronic myeloid leukaemia (CML) and some cases of acute lymphoblastic leukaemia. To assess the impact of bcr-abl upon haemopoiesis, lethally irradiated mice were reconstituted with bone marrow cells enriched for cycling stem cells and infected with a bcr-abl bearing retrovirus. The mice developed several fatal diseases with abnormal accumulations of macrophage, erythroid, mast and lymphoid cells, and marked strain differences in disease distribution and kinetics. Some mice exhibited more than one neoplastic cell type and, in some instances, these were clonally related, indicating that a progenitor or stem cell had been transformed. While classical CML was not observed, the macrophage tumours were accompanied by a mild CML-like syndrome, probably due to myeloid growth factor production by tumour cells. The erythroid and mast cell diseases were rarely transplantable, in contrast to the macrophage tumours and lymphomas, but all disease types displayed limited clonality. These results establish that bcr-abl confers a proliferative advantage on diverse haemopoietic cells but complete transformation probably involves additional genetic changes.

Morphological and Functional Changes in the Rat Heart after X Irradiation: Strain Differences

The hearts of mature male rats of the Wistar and Sprague-Dawley strains were locally irradiated with single doses of 17.5 and 20.0 Gy of X rays, respectively. These two dose levels had previously been shown to result in a comparable latent period between irradiation and the death of rats of these two strains from cardiac failure. Morphological changes in the myocardium and modifications in cardiac function were assessed in the animals at 28, 70, and 100 days after irradiation. The first radiation-induced change which was observed in the myocardium was a rapid decline in capillary density and a loss of alkaline phosphatase activity by the capillary endothelial cells. The capillary density was reduced to approximately 50% of that of unirradiated control values at 28 days and to approximately 40% of the control values between 70 and 100 days after irradiation. The loss of enzyme activity was also detected at 28 days. Examination of histological sections showed an increase by 70 days in the areas with negative enzyme activity up to approximately 70% of the myocardium. The reduction in capillary density and the loss of enzyme activity occurred before any marked pathological changes were seen in the myocardium. The pathological lesions seen in the myocardium at 100 days after irradiation were qualitatively and quantitatively the same in the two strains of rat. Measurements of cardiac output in Sprague-Dawley rats showed a gradual decline in output after irradiation; however, measurements in Wistar rats showed a progressive increase in cardiac output over the same period of time. It was shown by rubidium extraction that there was an increase in the percentage of the total cardiac output distributed to the ventricular muscle of Sprague-Dawley rats, while similar measurements in Wistar rats showed no significant change. In spite of the marked strain differences observed in cardiac output and rubidium extraction, blood perfusion per gram of ventricular muscle was apparently not modified in both strains of rat after irradiation. These findings indicated that the correlation between morphological effects after irradiation and the functional expression of damage is highly complex.

The effect of volume per cent of phase on the high temperature tensile deformation of two-phase TiMn alloys

Abstract The high temperature (973 K) tensile deformation behavior of α, β and α-β TiMn alloys was studied as a function of volume per cent of the component phases and strain rate (2.6 × 10−2 − 10−4 s−1). Marked yield drops and strain softening were observed in the β phase, and the extent of drop increased with strain rate. Experiments indicated that the yield drop was not due to the declustering phenomenon. The yield drop was attributed to a sudden increase in the mobile dislocation density, and the apparent strain softening was attributed to the process of dynamic recovery. The flow stresses of the α-β alloys did not vary linearly with the volume per cent of β and did not follow the rule of mixture law based on constant stress or constant strain. The extent of deviation from linearity depended on the volume per cent of β and the strain rate. The strength of an α-β alloy with nearly equal volume per cents of the phases was found to be significantly lower than expected. This was attributed to the interface-sliding phenomenon in this alloy. Yield drops were also observed in α-β alloys, and the extent of yield drop and the apparent strain softening increased with increase in β content and strain rate. The finite element method was used to show that the local stresses in the β phase reach the critical flow stress required to cause the yield drop even though the overall applied stress in α-β alloys is much lower than this stress, resulting in flow stress drops in α-β alloys.

Influence ofGlycine max nodulation on the persistence in soil of a genetically markedBradyrhizobium japonicum strain

Since competition with indigenous strains limits nodule occupancy by bacteria applied to seeds, the ecology of Bradyrhizobium inoculum strains used for soybean is of concern. A genetically marked strain,B. japonicum I-110 ARS, was directly enumerated from soil on selective medium. A clear long-term positive influence of even limitedGlycine max nodulation was shown by comparisons of population densities obtained with or without plant removal prior to nodule senescence in the first year and with an incompatible as well as a compatible soybean variety after 5 years.

Evaluation of the retrograde contamination guard in a bacteriologically challenged rabbit model.

We compared a newly developed closed urinary drainage system incorporating a retrograde contamination guard (RCG) with the conventional closed drainage system. The new system contains a solid bactericide (povidone iodine) pellet enclosed in a porous cartridge at the drain port of the urine collection bag. A catheterised rabbit model was used. The urine drainage bags were challenged daily for 8 days with an auxotrophically marked uropathogenic strain of Escherichia coli at the outlet tube. The bag urine was infected with the marked organism in 10 of the 11 rabbits in the control group (conventional collection bags) in 3.8 +/- 1.03 days and in only 1 of the 13 rabbits fitted with the RCG. The RCG effectively prevents contamination of the urine drainage bag and thus may play an important role in reducing the incidence of nosocomial urinary tract infections.

Job strains and job satisfaction of dialysis nurses.

Results are reported from an investigation on job strains in dialysis nurses and needs for psychosocial staff training. 174 dialysis nurses in the Federal Republic of Germany answered the clinical questionnaire, which was distributed in cooperation with the German section of the EDTNA. Although the majority emphasized positive aspects of the job (particularly responsible work, contact to patients, and teamwork), more than one-fourth of the nurses reported marked psychosocial strains. Main sources of stress were doubts about the principle of maximum therapy, the consumerism of some patients, and intrateam tensions. Almost two-thirds confirmed the necessity of psychosocial staff training, favoring training units of 1-2 h once a month. In the staff's opinion psychosocial staff training should mainly include casework and cognitive as well as behavioral training for a better handling of patients and conflicts. Main topics suggested by the nurses for discussion were depression, coping with illness as well as handling of aggressive and pretentious patients. Finally, implications of the findings with respect to the goals and performance of psychosocial staff training are discussed.

Bacillus subtilis B-2 and selected onion rhizobacteria in onion seedling rhizospheres: Effects on seedling growth and indigenous rhizosphere microflora

Marked strains of Bacillus subtilis B-2 and four selected rhizobacteria were introduced into onion rhizospheres by seed bacterization. Their effects on plant growth and their populations in root surface and root zone soil environments of field-grown onions were estimated 30 days following sowing. Populations of indigenous rhizosphere bacteria and fungi were also assessed by dilution plating. Seed bacterization with B-2 UI-1 and B caused significant increases in shoot height and shoot dry weights of onion seedlings over controls. Only UI-2 caused a significant increase in root dry weight. All of the strains survived in seedling rhizopheres in substantial numbers, but there were marked differences among the strains. Overall, UI-2 and B were comparatively good colonizers, UI-1 and W were intermediate and B-2 was poor. Seed bacterization treatments significantly reduced indigenous bacterial and fungal populations in seedling rhizospheres. Promotion of onion seedling growth by seed bacterization was not correlated with the relative persistance of the introduced bacterium, but may be related to the ability of the introduced bacterium to reduce components of the indigenous rhizosphere microflora.

Strain difference and mode of inheritance of the susceptibility to passive cutaneous anaphylaxis mediated by allogeneic IgE antibody in the mouse.

The strain difference and mode of inheritance of the susceptibility to PCA (passive cutaneous anaphylaxis) were studied in mice. No marked strain differences were found in the susceptibility to PCA mediated by allogeneic IgG1 monoclonal and xenogeneic IgG antibodies, although BALB/c Crj mice were somewhat less susceptible than the other strains. On the other hand, the susceptibility to PCA mediated by allogeneic IgE monoclonal antibodies differed greatly according to the strain; SJL/J, A.SW/J and DS/Shi mice being highly susceptible and C57BL/6JShi, BALB/cCrj, DBA/2Crj, C3H/HeShi and CBA/JNCrj mice insusceptible. Based on the marked difference between DS/Shi and C3H/HeShi strains, the mode of inheritance of the susceptibility to IgE PCA was studied using their F1, F2 and F1 x parent backcross offspring. All the F1 hybrids by reciprocal crosses between these two strains and F1 x DS backcross mice were highly susceptible like DS/Shi mice. Backcross mice between F1 and C3H/HeShi showed approximately 1:1 segregation into the susceptible and insusceptible. Segregation was also observed in the F2 generation; 32% being insusceptible. These results suggest that the high susceptibility is a dominant phenotype controlled mainly by a single gene on an autosomal chromosome; this was statistically supported by tests of the segregation ratios obtained. However, in the PCA-positive recipients of F1 x C3H backcross and F2 generations, dye leakage into the skin was tended to be diffuse and less compact than in DS/Shi, F1 and F1 x DS backcross mice. This suggests the presence of some additional genes which modify the expression of the main gene.

Growth effects associated with seed bacterization not correlated with populations of Bacillus subtilis inoculant in onion seedling rhizospheres

Populations of a marked strain of the B-2 isolate of Bacillus subtilis (B-2) in the rhizospheres of onion seedlings grown from bacterized seeds in muck soil at various pH, moisture and temperature regimes were monitored for 14 weeks. Irrespective of regime, populations of B-2 in onion rhizospheres declined rapidly within the first 14 days after seeding, from 4.8 × 10 6 cfu per seed on day zero to a mean of 1.1 × 10 3 cfu per plant at day 14, and less rapidly during the next 12 weeks following seeding. An average population of 9.5 × 10 1 cfu per plant was recovered at 14 weeks following seeding. Within the pattern of general decline, survival of B-2 in the rhizosphere was favored by high temperature, high moisture and high pH regimes; temperature appeared to be the most important variable. Seed bacterization significantly increased shoot dry weight (12–94%), root dry weight (13–100%) and shoot height (12–40%) of onion seedlings over controls. Increases in shoot height and shoot weight were greatest at low temperature and high moisture, under all pH regimes. Root weight was similarly affected by temperature and moisture, but was significantly increased at pH 6.5 compared to 5.5 and 4.5. Though B. subtilis B-2 failed to maintain high populations in the onion rhizosphere, it nevertheless caused significant growth effects on bacterized onion seedlings. The observed growth effects were not proportional to rhizosphere populations of B-2.

Survival and dispersal of a marked strain of Pseudomonas syringae in a maple nursery

A pathogenic Pseudomonas syringae strain resistant to rifampicin and nalidixic acid was sprayed upon and colonized maple twigs and perennial ryegrass. The inoculated twigs were sampled at intervals of 2‐3 weeks from July 1985 to September 1986, and epiphytic populations of the marked strain recovered during this time ranged from undetectable to 104 colony‐forming units/g. The results showed that this strain of P. syringae could overwinter on maple twigs and potentially serve as a source of inoculum in the spring. Aerial dispersal was also investigated. The marked strain inoculated onto grass growing in pots was detected on medium in inverted petri plates, on maple leaves and with an Andersen sampler positioned from 12 to 100 cm above the grass. The number of detectable cells that dispersed vertically upwards was low even in the presence of wind, rain, or irrigation water. The marked strain inoculated onto maple branches was isolated from grasses under the inoculated trees, showing that P. syringae was dispersed downward. Lateral dispersal of the marked strain from inoculated to uninoculated trees was not detected. The identity of the antibiotic‐resistant strain isolated from the trees and grasses was confirmed by DNA restriction‐fragment profile analysis.

Survival of rifampin-resistant mutants of Pseudomonas fluorescens and Pseudomonas putida in soil systems.

The fate of spontaneous chromosomal rifampin-resistant (Rifr) mutants of Pseudomonas putida and Pseudomonas fluorescens in sterile and live organic soil from which they were isolated was studied. In sterile native-soil assays, a Rifr mutant of P. putida showed no decrease in competitive fitness when compared with the wild-type parent. However, mutants of P. fluorescens were of two general categories. Group 1 showed no difference from the wild type in terms of growth rate, competitive fitness, and membrane protein composition. Group 2 showed a slower growth rate in both minimal and enriched media and an altered membrane protein profile. These mutants also demonstrated decreased competitive fitness compared with the wild-type strain. In live soil, the Rifr P. putida strain persisted throughout the 38-day test period with a decay rate of 0.7 log10 CFU/g of soil per 10 days. A group 1 Rifr P. fluorescens mutant maintained its inoculated titer for 7 to 10 days and then decayed at a rate of 0.2 to 0.4 log10 CFU/g of soil per 10 days. A group 2 Rifr P. fluorescens mutant remained at its titer for 1 to 5 days before decaying at a two- to threefold-faster rate. These findings indicate that rifampin resistance may not be an innocuous mutation in some pseudomonads and that marked strains should be compared with wild-type parents before being used as monitors of parental strain survival. Colonization of sterile soil with either the wild-type or mutant strain precluded normal colonization of the second added strain.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of electrophoretic karyotypes in the classification of yeasts: Kluyveromyces marxianus and K. lactis

The relationship between varieties “marxianus” and “lactis” of Kluyveromyces marxianus was investigated. Strains of these varieties readily form hybrids, but their classification in one species has recently been contested. Enzyme patterns and the GC contents of their DNAs differed significantly. Moreover, DNA-DNA reassociation was less than 15%. Since the generally accepted definition of a species is based on gene exchange, we used two approaches for directly detecting genetic recombination in crosses between representatives of both species. First, multiple marked strains were crossed, and the offspring from the resulting hybrids analyzed. Secondly, the fate of individual chromosomes in identical crosses was followed by comparing the karyotypes of the parent strains, the hybrids formed between them, and the descendants of these hybrids. Karyotypes were obtained by orthogonal-field-altemation gel electrophoresis (OFAGE). Gene exchange was not detected with either method. We therefore concluded that the formation of hybrids, even when they produced viable offspring, was not sufficient to include var. “lactis” and var. “marxianus” in one species.

Genomic exclusion and other micronuclear anomalies are common in genetically defective clones of tetrahymena thermophila.

Genomic exclusion (GE) is an abnormal form of conjugation which has previously been described in detail for three hypodiploid strains of Tetrahymena thermophila. These strains cannot form gametic nuclei and by failing to participate in normal reciprocal fertilization their genes are excluded from exconjugants. To determine whether GE is a general property of infertile strains, we surveyed genetically and cytogenetically 19 additional strains of T. thermophila to determine why they failed to contribute genes to sexual progeny. Crosses to genetically marked tester strains showed that seventeen of these strains undergo GE. In each case GE appears to be due to the failure of the defective partner to form functional gametic nuclei. The normal conjugant, however, contributes to its defective partner a haploid nucleus identical to its own, and following diploidization of the unfertilized nuclei, the conjugants separate retaining the old macronuclei. Cytofluorimetric measurement of micronuclear DNA content in 18 strains suggests that aneuploidy is the proximate cause of GE; eleven strains were hypodiploid, five were diploid and three were hyperdiploid. Many irregular cytogenetic events were observed in conjugants presumably not undergoing GE, including, in some instances, abnormal meiosis in the normal partner. Since genomic exclusion was found in both wildtype and mutant clones, the results suggest that it should be possible by appropriate crosses to identify genomic exclusion strains of any genotype.

A physical method for separating Saccharomyces cerevisiae cells according to their ploidy.

A centrifugation technique, using genetically marked Saccharomyces cerevisiae strains, has been developed to separate Saccharomyces cerevisiae cells of different ploidy levels from exponential phase cultures. The method involves the conversion of yeast cells to protoplasts, the separation of the protoplasts on an osmotically stabilized Nycodenz gradient, and their regeneration. This type of selection may be of importance where selectable markers are not available.

Strain dependence in mice of resistance and susceptibility to the testicular effects of cadmium: Assessment of the role of testicular cadmium-binding proteins

The nature of the cadmium (Cd)-binding proteins in the mouse testes is unknown, although some studies have implied metallothionein (MT) is responsible for the marked strain dependence of Cd-induced testicular necrosis in mice. This study attempted to define the role of MT in strain-dependent Cd resistance using NFS (susceptible) and BALB/c (resistant) mice. In all cases, testicular proteins were compared to hepatic MT isolated after treatment with zinc (Zn). A low-molecular-weight ( M r) Zn-, Cd-binding protein was detected in testicular and hepatic cytosol from both strains after gel filtration. These proteins were extractable by heat treatment and sequential acetone precipitation. When such extracts were further purified with reversephase HPLC, two forms of authentic MT were shown by amino acid analysis from both NFS and BALB/c livers. However, of two testicular forms separated by HPLC from NFS and BALB/c mice, neither could be classified as MT based on amino acid composition. Methylation of the MT-I gene was also studied in testicular and hepatic DNAs isolated from control mice or from mice made resistant to Cd-induced testicular necrosis by Zn treatment. Major differences in methylation between tissues were seen, as the testicular gene of both NFS and BALB/c mice was highly methylated, a condition often linked to genetic quiescence. Zn treatment had no effect on MT-I gene methylation in testes of either strain, although rendering the NFS strain resistant to Cd. Zn treatment did not alter levels of this testicular protein in either strain while causing a marked induction of hepatic MT in both. These results indicate the low- M r Cd-, Zn-binding proteins present in the testes of both resistant and susceptible mice are not MTs and further that the MT gene may not be expressed in either strain.

Colonization resistance of the human intestinal microflora: Testing the hypothesis in normal volunteers

Colonization resistance is the mechanism whereby the intestinal microflora protects itself against incursion by new and often harmful microorganisms. Some authors have claimed that colonization resistance is related to the integrity of the anaerobic flora, but this point has not been established in humans. In previous studies in our laboratory cefoxitin, piperacillin, cefoperazone or aztreonam were administered intravenously to healthy volunteers in order to study changes in the intestinal flora and acquisition of new strains. Seven of 16 antibiotic-treated subjects were colonized with gram-negative bacilli, but no correlation was observed between this colonization and the suppression of either anaerobes or any other component of the fecal flora. Marked strains of Escherichia coli and Pseudomonas aeruginosa were also administered by mouth in order to test acquisition of new bacteria. The fed bacteria were found in the stools of both antibiotic-treated and control subjects; the antibiotics had no apparent influence on the ability of these strains to colonize the intestinal tract. Our work, along with findings of others, supports the concept that colonization resistance occurs in humans and is diminished by antibiotic administration. However, it does not support the hypothesis that colonization resistance is related to the anaerobic microflora.

A Comparison of hydrogen and mercury embrittlement in aisi 4142 steel

Slow strain rate tensile tests, and some fatigue tests, were run at room temperature in the environments of air, liquid mercury and hydrogen. The hydrogen was generated electrolytically, with the charging and testing commencing simultaneously. The specimens were quenched and tempered to a range of hardness levels. The embrittlement by hydrogen and by mercury differed in several aspects. In hydrogen alone, there was a loss of tensile strength, a marked strain rate sensitivity, and a crack progression of transgranular to intergranular to microvoid coalescence. In mercury, the crack initiation was intergranular. It is believed that the hydrogen induced transgranular cracking is plasticity related with hydrogen penetration occurring at an enhanced rate. This situation would not arise with mercury.

Induced parasexual processes in Claviceps sp. strain SD58.

A homokaryotic, clavine alkaloid-producing strain of ergot, Claviceps sp. strain SD 58, was used in an attempt to demonstrate parasexuality. Genetically marked auxotrophic strains were produced by mutation with N-methyl-N'-nitro-N-nitrosoguanidine. Protoplast fusion of pairs of unlike doubly auxotrophic strains and isolation of stable prototrophic fusion products were carried out. By growth of the fusion products on complete medium, selective pressure for prototrophy was removed and auxotrophic segregants were allowed to form. Analysis of these and recovery of segregants with nonleaky, non-parent-type combinations of auxotrophic characteristics has provided strong evidence that a parasexual cycle can function in Claviceps sp. strain SD 58. Preliminary work suggests that the genetics of ergot might be studied by mitotic analysis and that protoplast fusion and selection procedures might be useful for the enhancement of favorable characteristics in Claviceps strains.

Genetic control of the population size of the melanocyte in the mouse epidermis.

BY Tomohisa HIROBE Department of Biology, Faculty of Education, Iwate University, Ueda, Morioka 020 (Received December 8, 1986) ABSTRACT Hair bulb melanocytes involved in the expression of the coat colors of mice are derived from epidermal melanocytes. The biological study of epidermal melanocytes is important to understand the expression of the coat color. Analysis of the melanocyte and melanoblast-melanocyte population in the mouse epidermis has shown marked strain differences, suggesting that the two populations are regulated by genetic factors. From the results of genetic crosses between C57BL/1OJ and C3H/He mice semidominant genes were shown to be involved in regulating the two populations. The two populations in C57BL/1OJ-A/A congenic mouse did not differ from those in C57BL/1OJ. The distributions of the two populations in C3H/He were gradually transferred to those in C57BL/1OJ by repeated backcrossing. The semidominant genes are thought to affect the melanocyte proliferation, melanocyte differentiation, or induction of tyrosinase activity by MSH. Such effects may change the pigmentation in the hair bulb and produce a variety of the hair color intensity of mice, which may in turn be influenced by selec-tion, mutation, random mating, and environment.

Influence of mouse genotype on responses of central cholinergic neurotransmission to long term alcohol intoxication

Cholinergic neurotransmission has been followed in striatum and hippocampus in two inbred strains of mice (C57Bl/6 and Balb/c) during long term alcohol exposure (over a 25 month period) and with aging. Marked strain dependent differences in reactivity of pre- and postsynaptic cholinergic markers to chronic alcohol exposure and aging were demonstrated in both structures. The Balb/c strain exhibits a remarkable long lasting tolerance to alcohol injury for striatal and hippocampal cholinergic markers (choline acetyltransferase, high affinity choline uptake, muscarinic receptors affinity, acetyl cholinesterase), whereas C57Bl mice appear more sensitive to alcohol intoxication. Likewise aging affects the C57Bl mouse more severely than the Balb/c, a phenomenon which may be involved in the sensitivity of these mice to alcohol intoxication. Moreover long term alcohol exposure, in addition to aging show unequal effects on the diverse cholinergic markers studied. Also divergences of specific brain areas have been noted and should be related to their particular neuroanatomy. Such discrepancies may, in part, explain differences observed in the behavioral effects of chronic alcohol intoxication in alcoholics.