Haplotype-specific suppression of antibody responses in vitro. III. Haplotype-specific suppressor factor (TsF-H) binds to but fails to suppress responses by the I-A mutant strain B6.C-H-2bm12

Spleen cells from C57BL/6 and B6.C-H-2bm12 mice, both responder strains to GAT, differ in their ability to be suppressed by the monoclonal I-A-restricted, nonantigen-specific, but haplotype-specific suppressor factor, TsF-H, from the hybridoma 266A4.5. Whereas GAT-specific responses by C57BL/6 spleen cells are susceptible to TsF-H-mediated suppression, responses by bm12 spleen cells are nonsuppressible under the same conditions. Responses of both C57BL/6 and bm12 spleen cells are suppressed by monoclonal GAT-specific suppressor factors. The inability of TsF-H to suppress responses by the bm12 spleen cells presumably reflects the effects of the mutation in the beta-chain of the I-A antigen in this strain on the required I-A restriction between TsF-H and target cell for manifestation of suppressive activity. The data are discussed in terms of involvement of I-A or recognition of I-A in mediating suppression.     

The Relationship between the Distribution of Common Carp and Their Environmental DNA in a Small Lake

Although environmental DNA (eDNA) has been used to infer the presence of rare aquatic species, many facets of this technique remain unresolved. In particular, the relationship between eDNA and fish distribution is not known. We examined the relationship between the distribution of fish and their eDNA (detection rate and concentration) in a lake. A quantitative PCR (qPCR) assay for a region within the cytochrome b gene of the common carp (Cyprinus carpio or ‘carp’), an ubiquitous invasive fish, was developed and used to measure eDNA in Lake Staring (MN, USA), in which both the density of carp and their distribution have been closely monitored for several years. Surface water, sub-surface water, and sediment were sampled from 22 locations in the lake, including areas frequently used by carp. In water, areas of high carp use had a higher rate of detection and concentration of eDNA, but there was no effect of fish use on sediment eDNA. The detection rate and concentration of eDNA in surface and sub-surface water were not significantly different (p≥0.5), indicating that eDNA did not accumulate in surface water. The detection rate followed the trend: high-use water > low-use water > sediment. The concentration of eDNA in sediment samples that were above the limit of detection were several orders of magnitude greater than water on a per mass basis, but a poor limit of detection led to low detection rates. The patchy distribution of eDNA in the water of our study lake suggests that the mechanisms that remove eDNA from the water column, such as decay and sedimentation, are rapid. Taken together, these results indicate that effective eDNA sampling methods should be informed by fish distribution, as eDNA concentration was shown to vary dramatically between samples taken less than 100 m apart.     

Stepwise incorporation of white clover (Trifolium repens L.) as fertiliser increases nitrogen fixation and improves nitrogen retention when intercropped with leek (Allium porrum L.)

Plant and Soil - We investigated whether the incorporation of intercropped white clover as a split-dose fertiliser improves N retention of the plant-soil system in leek production. White clover and...     

RELATIONSHIP BETWEEN SELF-FERTILITY,ALLOCATION OF GROWTH,AND INBREEDING DEPRESSION IN THREE CONIFEROUS SPECIES

Mortality and growth of self and outcross families of three wind-pollinated, mixed-mating, long-lived conifers, Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), and noble fir (Abies procera) were followed from outplanting to age 26 (25 for noble fir) in spaced plantings at a common test site. Response to inbreeding differed greatly among species over time and in all regards. Only Douglas-fir and noble fir will be contrasted here, because ponderosa pine usually was intermediate to the other two in its response to inbreeding. In earlier reports, compared to noble fir Douglas-fir had a higher rate of primary selfing and larger inbreeding depression in seed set. Douglas-fir continued to have higher inbreeding depression in nursery and early field survival. The species differed in time courses of inbreeding depression in height and in allocation of growth due to crowding. Between ages 6 and 12, the relative elongation rate (dm · dm^?1 · yr^?1) of Douglas-fir was significantly greater in the selfs than in the outcrosses. The response was not observed in noble fir. At final measurement, inbreeding depression in diameter relative to inbreeding depression in height was greater in Douglas-fir than in noble fir. At final measurement inbreeding depression in height was inversely related to inbreeding depression in survival. Cumulative inbreeding depressions from time of fertilization to final measurement were 0.98, 0.94, and 0.83 for Douglas-fir, ponderosa pine, and noble fir, respectively, which indicates that selfs will not contribute to the mature, reproductive populations.     

The accumulation of chromosome aberrations and Dlb-1 mutations in mice with highly fractionated exposure to gamma radiation

The dichotomy between the doses at which experimental measurements of genetic effects can be made and the doses to which people are exposed is often different by two or more orders of magnitude. This presents a significant problem when determining the effects of low doses of radiation or chemicals. The solution has usually involved extrapolating the data by curve-fitting or by applying theoretical considerations. Both approaches are unsatisfactory due to uncertainties of the assumptions used in each process. The alternative solution has been to increase the sample size enormously at the lower doses. This is impractical beyond a certain point due to the variation in the spontaneous frequency and the need to quadruple the sample size for a doubling of precision. The development of new methods for measuring stable genetic effects, however, permits a simple and effective approach to this problem: if the genetic events being detected have no effect on survival, i.e., are selectively neutral, then the effects of multiple independent treatments will be additive. If the independent treatments are identical, then the effect of each is easily calculated by dividing the total effect by the number of treatments. Here we report a limited test of this approach using mice. Chromosome aberrations induced in lymphocytes and Dlb-1 mutations induced in the small intestine were measured after daily doses of 0.64, 1.85 or 5.5 cGy ¹³⁷Cs gamma rays administered for 21, 42 or 63 days. The dose response curve for chromosome translocations obtained in this way, combined with the data from single larger acute doses, shows no evidence for a threshold over a 500-fold dose range. Dlb-1 mutations were increased at each dose and time but the results do not permit reliable extrapolations. The results suggest that translocations might be useful for quantifying the effect of doses below 0.05 cGy and that the effect of dose rate and dose fractionation at much lower doses than reported here could be investigated.     

Parasite influences on host life history: Echinostoma revolutum parasitism of Lymnaea elodes snails

Using field surveys and experimental infections, we investigated the influence of a trematode parasite on life history traits of adult Lymnaea elodes snails. We found that parasitism significantly affected the growth, fecundity, and survival of host snails. Within five of the six natural L. elodes populations we sampled, shell length of echinostome-infected hosts was significantly greater than for uninfected conspecifics. Furthermore, we show that gigantism occurs among experimentally infected snails due to an accelerated growth rate and size-selective mortality following an Echinostoma revolutum infection. The fecundity of infected snails sharply decreased beginning at 3 weeks post exposure (PE) and all egg production eventually ceased for most hosts by 5–6 weeks PE. Energy constraints, imposed by parasite development, alter the host energy budget. Early in the infection, parasite depletion of host energy reserves reduces host reproduction, but sufficient resources remain to allow accelerated host growth. Mortality was increased among host snails at two distinct stages: shortly after exposure and several weeks after cercariae were first released. We did not observe tissue degradation in snails during the first 4 weeks after exposure to the parasite, but destruction of host tissues was noted among snails dying later in the infection. Received: 5 September 1997 / Accepted: 19 November 1997     

Detection of differentially expressed genes in primary tumor tissues using representational differences analysis coupled to microarray hybridization.

The identification of differential gene expressionbetween cells is a frequent goal in modern biological research. Here we demonstrate the coupling of representational difference analysis (RDA) of cDNA with microarray analysis of the output for high throughput screening. Two primary Ewing's sarcoma tissue samples with different biological behavior in vivo were compared by RDA: one which was metastatic and progressed rapidly; the other localized and successfully treated. A modified RDA protocol that minimizes the necessary starting material was employed. After a reduced number of subtractive rounds, the output of RDA was shotgun cloned into a plasmid vector. Inserts from individual colonies from the subtracted library were amplified with vector-specific primers and arrayed at high density on glass slides. The arrays were then hybridized with differentially fluorescently labeled starting amplicons from the two tissues and fluorescent signals were measured at each DNA spot. We show that the relative amounts of fluorescent signal correlate well with the abundance of fragments in the RDA amplicon and in the starting mRNA. In our system, we analyzed 192 products and 173 (90%) were appropriately detected as being >2-fold differentially expressed. Fifty unique, differentially expressed clones were identified. Therefore, the use of RDA essentially provides an enriched library of differentially expressed genes, while analysis of this library with microarrays allows rapid and reproducible screening of thousands of DNA molecules simultaneously. The coupling of these two techniques in this system resulted in a large pool of differentially expressed genes.     

Trimethoprim-sulphamethoxazole in Acute Brucellosis

Eight patients with proved brucella infection were treated with trimethoprim-sulphamethoxazole. The dose varied from two to four tablets given twice daily for three weeks. Clinical response was rapid and all patients were asymptomatic and afebrile within two to seven days of starting therapy. Three patients relapsed clinically and bacteriologically within three weeks of ending treatment. There were no side effects of the treatment. It is suggested that the treatment be continued for at least six weeks to prevent relapses.