Selecting representative model micro-organisms

Background  

Micro-biological research relies on the use of model organisms that act as representatives of their species or subspecies, these are frequently well-characterized laboratory strains. However, it has often become apparent that the model strain initially chosen does not represent important features of the species. For micro-organisms, the diversity of their genomes is such that even the best possible choice of initial strain for sequencing may not assure that the genome obtained adequately represents the species. To acquire information about a species' genome as efficiently as possible, we require a method to choose strains for analysis on the basis of how well they represent the species.     

The structure of V alpha and J alpha segments in the mouse.

Antigen receptors on most T-cells are heterodimeric glycoproteins, comprised of an alpha chain and a beta chain. These chains are encoded by discontiguous variable (V), diversity (D) and joining (J) gene segments that rearrange to produce a contiguous and functional alpha or beta chain gene. To investigate the size and diversity of the germline repertoire of alpha-chain gene segments, we have characterized and sequenced 20 alpha chain cDNAs. Among these cDNA clones, we have found 4 J alpha and 4 V alpha sequences that have not yet been described. The relationship of these "new" gene segments to those already characterized is discussed.     

Maturation proteins associated with desiccation tolerance in soybean

A set of proteins that accumulates late in embryogenesis (Lea proteins) has been hypothesized to have a role in protecting the mature seed against desiccation damage. A possible correlation between their presence and the desiccation tolerant state in soybean seeds (Glycine max L. Chippewa) was tested. Proteins that showed the same temporal pattern of expression as that reported for Lea proteins were identified in the axes of soybean. They were distinct from the known storage proteins and were resistant to heat coagulation. The level of these “maturation” proteins was closely correlated with desiccation tolerance both in the naturally developing and in the germinating seed: increasing at 44 days after flowering, when desiccation tolerance was achieved, and decreasing after 18 hours of imbibition, when desiccation tolerance was lost. During imbibition, 100 micromolar abscisic acid or Polyethylene glycol-6000 (−0.6 megapascals) delayed disappearance of the maturation proteins, loss of desiccation tolerance, and germination. During maturation, desiccation tolerance was prematurely induced when excised seeds were dried slowly but not when seeds were held for an equivalent time at high relative humidity. In contrast, maturation proteins were induced under both conditions. We conclude that maturation proteins may contribute to desiccation tolerance of soybean seeds, though they may not be sufficient to induce tolerance by themselves.     

Two better cell lines for making hybridomas expressing specific T cell receptors

Two variants of the AKR thymoma BW5147 have been isolated which can no longer express functional TCR alpha- and beta-chains. By generating hybridomas with these variant fusion lines, TCR of any normal T lymphocyte, including TCR-gamma/delta, can be studied at a clonal level, without interference of the BW5147-derived receptor chains. In this study one of the variants has been useful in identifying the reactivity to allogeneic MHC Ag of BW5147 itself.     

Use of a recombinant baculovirus product to measure naturally-acquired human antibodies to disulphide-constrained epitopes on the P. falciparum merozoite surface protein-1 (MSP1)

Abstract An enzyme-linked immunosorbent assay (ELISA) has been developed to measure antibody levels in human sera to a candidate vaccine antigen, merozoite surface protein-1 (MSP1), of the malaria parasite Plasmodium falciparum . To ensure the detection of antibodies reactive with important conformational epitopes, antigens used in the ELISA were obtained from either in vitro parasite cultures, or from a baculovirus expression system in which correct folding of recombinant MSP1-derived polypeptides has been previously demonstrated. The specificity of the ELISA was confirmed using a novel antibody affinity select method. The assay was used to investigate the pattern of acquisition of anti-MSP1 antibodies in a cross-sectional survey of 387 3–8 year old residents of a malaria endemic area of the Gambia. A significant positive correlation between anti-MSP1 antibody levels and age was evident, though individual responses to two antigens corresponding to two distinct domains of the MSP1 varied widely.     

Desiccation tolerance in developing soybean seeds: The role of stress proteins

The consistent correlation between desiccation tolerance in orthodox seed tissue and an accumulation of certain "late embryogenesis abundant" (LEA) proteins suggests that these proteins reduce desiccation-induced cellular damage. The aim of the present work was to test this hypothesis. Exogenous abscisic acid (ABA) was used to elevate the level of heal-soluble LEA-like proteins in axes from immature (30 days after flowering: mid-development) seeds of soybean ( Glycine max [L.] Merrill cv. Chippewa 64). As the LEA-like proteins accumulated in response to ABA, the leakage of all elements after desiccation and subsequent rehydration markedly declined. Both LEA-like protein accumulation and the decline in desiccation-induced electrolyte leakage were apparently dependent on the presence of ABA. Both effects of ABA were inhibited by cycloheximide. Light microscopy revealed a marked effect of the ABA on cellular integrity following desiccation. Osmotic stress also caused a decrease in desiccation-induced electrolyte leakage and stimulated the accumulation of LEA-like proteins. Our data are consistent with the hypothesis that the LEA-like proteins contribute to the increase in desiccation tolerance in response to ABA, and are consistent with a general protective role for these proteins in desiccation tolerance.     

Frequency-dependent interference by magnetic fields of nerve growth factor-induced neurite outgrowth in PC-12 cells

We have shown that 50 Hz sinusoidal magnetic fields within the 5-10 micro Tesla (μT) rms range cause an intensity-dependent reduction in nerve growth factor (NGF) stimulation of neurite outgrowth (NO) in PC-12 cells. Here we report on the frequency dependence of this response over the 15-70 Hz range at 5 Hz intervals. Primed PC-12 cells were plated in collagen-coated, 60 mm plastic petri dishes with or without 5 ng/ml NGF and were exposed to sinusoidal magnetic fields for 22 h in a CO₂ incubator at 37 °C. One 1,000-turn coil, 20 cm in diameter, generated vertically oriented magnetic fields. The dishes were stacked on the center axis of the coil to provide a range of intensities between 3.5 and 9.0 μT rms. The flux density of the ambient DC magnetic field was 37 μT vertical and 19 μT horizontal. The assay consisted of counting over 100 cells in the central portion (radius ≤0.3 cm) of each dish and scoring cells positive for NO. Sham exposure of cells treated identically with NGF demonstrated no difference in the percentage of cells with NO between exposed and magnetically shielded locations within the incubator. Analysis of variance demonstrated flux density-dependent reductions in NGF-stimulated NO over the 35-70 Hz frequency range, whereas frequencies between 15 Hz and 30 Hz produced no obvious reduction. The results also demonstrated a relative maximal sensitivity of cells at 40 Hz with a possible additional sensitivity region at or above 70 Hz. These findings suggest a biological influence of perpendicular AC/DC magnetic fields different from those identified by the ion parametric resonance model, which uses strictly parallel AC/DC fields. © 1995 Wiley-Liss, Inc.     

The inheritance of natural chromosomal polymorphisms in the aphid Myzus persicae (Sulzer)

Two types of chromosomal abnormality have been found in natural populations of Myzus persicae in Japan. One type is apparently due to an autosome 3 dissociation, giving a 2n=13 karyotype. The other is interpreted as a translocation between autosomes 1 and 3, resulting in a 2n=12 complement with marked structural heterozygosity. In laboratory crosses, both types of abnormality were inherited through the sexual phase. The proportions of each type in the F₁ agreed well with expectations, except that no forms homozygous for the translocation were obtained from crosses between translocation heterozygotes, and no karyotypes with both the translocation and the dissociation were obtained when translocated and dissociated forms were crossed. In the F₁ of one cross a triploid clone with the autosomal 1,3 translocation was obtained.     

Effects of parathyroid hormone and calcitonin on adenylate cyclase in murine mononuclear phagocytes

Peritoneal mononuclear phagocytes elicited by thioglycollate demonstrate responsiveness to parathyroid hormone (PTH) and calcitonin (CT) which differs from that seen in the normal resident population. PTH causes a twofold stimulation of adenylate cyclase activity in elicited cells but inhibits this activity in resident cells. CT causes a greater stimulation of adenylate cyclase in elicited than in resident cells. Both CT and PTH cause an increase in cyclic AMP accumulation in cultures of elicited mononuclear phagocytes. These results indicate that cells of the mononuclear phagocyte lineage have functional receptors for both PTH and CT. This is the first biochemical evidence to support the hypothesis that mononuclear phagocytes are precursors of the bone resorbing osteoclast.