The use of stable isotopes to trace small-scale movements by small fish species

Valuable biological information can be obtained by monitoring the movement of organisms. However, the choice of monitoring method becomes highly restricted when following small organisms (<100 mm), especially in aquatic ecosystems. Stable isotopes are being increasingly used in this respect but rarely at the local spatial scale, i.e. 10–1000 s of metres. We sought to identify movement of small fishes between a main river channel and its tributary. Little overlap in isotope baseline was detected between the two channels despite some temporal variability in δ¹⁵N of baseline indicator organisms in the main river. The individuals of two small cyprinid fish species (Leuciscus souffia and Alburnoides bipunctatus) of all the size classes (40–100 mm) caught within the tributary showed considerable heterogeneity in δ¹⁵N values. Classification and discriminant analysis on isotope-derived data distinguished two significantly different groups. Moreover, this result was supported by further sampling of fish caught in the main river (in May and December 2006). Alternative hypotheses, such as dietary differences, biological factors, temporal shifts and spatial differences in diet, did not explain δ¹⁵N variability. This application of stable isotopes at a relatively small spatial and temporal scales further demonstrates its potential as a tool for ecologists.     

Mitochondrial heredity of resistance to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of cytochrome b oxidation, in Saccharomyces cerevisiae.

3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), an inhibitor of cytochrome b oxidation, has been used for the selection of three resistant mutants (diur) of Saccharomyces cerevisiae. The mutant diur-64 exhibits in vivo cross-resistance to antimycin A while diur-34 and diur-1 are more sensitive to antimycin A than the parental strain. The three mutants exhibit mitochondrial inheritance according to the following criteria: mitotic segregation of diuron-resistant and diuron-sensitive diploids is obtained among the diploid progeny of a cross between diur and dius; non-Mendelian segregation of diuron resistance (4:0) is observed in spores of tetrads issued from diuron-resistant diploid; extensive ethidium bromide treatment leads to the formation of Q- mutants which no longer transmit diur and dius alleles. Evidence for two distinct diuron-resistant loci were obtained by allelism tests. Recombination analysis shows that diuron-resistance is not located in the polar region of the mitochondrial genome. The diur loci are not linked to the erythromycin locus since the upper limit in recombinants frequency (26%) for a non-polar region is obtained between diur and eryr. A low recombinants frequency (3%) is observed in crosses between diur-34 mutation and the two mutants cob1 and cob2 suggesting that diur-34 might be located between these two cytochrome-b-deficient loci. The resistance to diuron is also expressed in vitro since the oxidation rates of succinate by sonicated submitochondrial particles from the mutants are clearly less sensitive to diuron than that of the wild type.     

Preparative electrophoresis on agarose submerged gels of two aggregating proteoglycan monomers from articular cartilage

Analytical electrophoresis on polyacrylamide-agarose gels of aggregating proteoglycan monomers from baboon articular cartilage produces two distinct bands, corresponding to two different aggregating monomer populations. A preparative electrophoresis procedure is described for isolating the two monomers. Proteoglycans were extracted from young baboon articular cartilage in 4 M guanidinium chloride containing proteolysis inhibitors and aggregated after hyaluronic acid addition. The aggregates were separated from non-aggregated proteoglycans by isopycnic centrifugation, followed by gel chromatography on Sepharose CL-2B. The monomers of the aggregates were obtained by isopycnic centrifugation under dissociative conditions. Two monomers were separated by preparative electrophoresis on 0.8 % agarose submerged gels. Approximately 60 % of the proteoglycans were recovered from the gel using a freeze-squeeze procedure. Aliquots of the separated monomers gave single bands when submitted to analytical polyacrylamide-agarose gel electrophoresis. Their migration and appearance were similar to that of the two bands present in the non separated preparation of monomers.     

DNA unwinding and inhibition of mouse leukemia L1210 DNA topoisomerase I by intercalators.

The DNA unwinding effects of some 9-aminoacridine derivatives were compared under reaction conditions that could be used to study drug-induced topoisomerase II inhibition. An assay was designed to determine drug-induced DNA unwinding by using L1210 topoisomerase I. 9-aminoacridines could be ranked by decreasing unwinding potency: compound C greater than or equal to 9-aminoacridine greater than o-AMSA greater than or equal to compound A greater than compound B greater than m-AMSA. Ethidium bromide was more potent than any of the 9-aminoacridines. This assay is a fast and simple method to compare DNA unwinding effects of intercalators. It led to the definition of a drug intrinsic unwinding constant (k). An additional finding was that all 9-aminoacridines and ethidium bromide inhibited L1210 topoisomerase I. Enzyme inhibition was detectable at low enzyme concentrations (less than or equal to 1 unit) and when the kinetics of topoisomerase I-mediated DNA relaxation was studied. Topoisomerase I inhibition was not associated with DNA swivelling or cleavage.     

A T cell surface molecule different from CD2 is involved in spontaneous rosette formation with erythrocytes

Increasing evidence indicates that rosettes which spontaneously from between human T cells and E might be of physiologic relevance. We show here that another T cell-surface molecule than CD2 is involved in rosette formation. Four mAb have been obtained reacting with human T cells that block rosettes with E from many species, including autologous cells. They react with a molecule, we termed E2, which is actively synthetized by T and monocytic cells. Immunoprecipitation revealed a major 32-kDa band. Immunoblots revealed a major 32-kDa band and a minor 20-kDa band. This molecule was detected on all T cells tested--and present at high densities on corticothymocytes, but at low densities on medullary thymocytes. It was also found on monocytes but not on B cells. However B-CLL cells did carry this molecule. E2 molecules were also detected on nonhematologic cells. Together with the recent evidence that 3 molecules from the erythrocyte surface are also involved for rosettes, intricate molecular interactions would account for adhesion of T cells to autologous E and possibly autologous nucleated cells.     

Nuclear DNA content and separation of Nicotiana sylvestris vegetative and generative nuclei at various stages of male gametogenesis

At all stages of male gametogenesis, generative and vegetative pollen nuclei of Nicotiana sylvestris can be distinguished without ambiguity after Feulgen or ethidium bromide staining. They differ by their morphology and their apparent DNA content, always lower in vegetative nuclei. These differences provide a basis for their separation by sedimentation and fluorometry. After elimination of the another somatic cells and after crushing the pollen, vegetative and generative nuclei are separated by two successive Percoll gradients (purity 80–90%). Analysis of the gradient fractions and final purification can be done with a cell sorter. DNAs of both types are isolated by a cetyltrimethylammonium method, followed by a RNase treatment. Yields are lower for vegetative than for generative nuclei, and decrease with the age of pollen. Molecular weights and digestibility by restriction enzymes are compatible with molecular analyses.     

Large E1B proteins of adenovirus types 5 and 12 have different effects on p53 and distinct roles in cell transformation.

The formation of complexes between oncoproteins of DNA tumor viruses and the cellular protein p53 is thought to result in inactivation of the growth suppressor function of p53. In cells transformed by nononcogenic human adenovirus type 5 (Ad5), the 55-kDa protein encoded by E1B forms a stable complex with p53 and sequesters it in the cytoplasm. However, the homologous 54-kDa protein of highly oncogenic Ad12 does not detectably associate with p53. Yet in Ad12-transformed cells, p53 is metabolically stable, is present at high levels in the nucleus, and contributes to the oncogenicity of the cells. Such properties have previously been described for mutant forms of p53. Here, we show that stable p53 in Ad12-transformed cells is wild type rather than mutant and that stabilization of p53 is a direct consequence of the expression of the Ad12 E1B protein. We also compared the effects of the E1B proteins on transformation of rodent cells by different combinations of oncogenes. A synergistic interaction was observed for the gene encoding the 54-kDa E1B protein of Ad12 with myc plus ras oncogenes, resembling the effect of mutant p53 on myc plus ras. In contrast, the Ad5 55-kDa E1B protein strongly inhibited transformation by myc plus ras but stimulated transformation by E1A plus ras. The data are explained in terms of different interactions of the two E1B proteins with endogenous p53. The results suggest that in cultured rat cells, endogenous wild-type p53 plays an essential role in cell proliferation, even in the presence of myc plus ras. The dependence on p53 is lost, however, when the adenovirus E1A oncogene is present.