Kin Discrimination in a Macropod Marsupial

Differential treatment of kin is ubiquitous in social animals. Parents often behave preferentially towards their dependent offspring. Species in several taxa also bias behaviour towards non-descendent kin. This latter phenomenon has not been demonstrated in marsupials, which are reportedly less social than eutherian mammals. We report the first evidence of non-parental kin-biased behaviour in a macropodid marsupial. Experimental pairing of individuals based on kinship reliably altered the rate of aggression between individuals in pairs of female tammar wallabies ( Macropus eugenii ). This effect is probably attributable to relatedness rather than to familiarity. Marsupial sociality may be substantially more complex than is currently recognized.     

High chromosomal sensitivity of Chinese hamster xrs 5 cells to restriction endonuclease induced DNA double-strand breaks

The cytogenetic effects of restriction endonucleases (RE) and X-rays were examined in the radiosensitive mutant Chinese hamster cell line xrs 5 and its normal parental line CHO K1. Cells were permeabilized with Sendai virus and exposed to Pvu II and Eco RV which induce blunt-ended double-strand breaks (dsb) in the DNA of cells, or Bam H1 and Eco R1 which induce cohesive-ended dsb with a four-base overlap. Treated cells were then assayed for the presence of metaphase chromosomal aberrations by sampling at multiple fixation times and in experiments where cells were exposed to graded series of RE concentrations. Exposure to X-rays or RE causing blunt-ended dsb was found to be between two and three times more effective in xrs 5 than in CHO K1 cells. We interpret this higher chromosomal sensitivity of xrs 5 cells as reflecting the reported defect in dsb repair in xrs 5. Both xrs 5 and CHO K1 cells yielded less aberrations after exposure to Bam H1 or Eco R1 than after exposure to Pvu II or Eco RV, confirming our previous results and demonstrating that cohesive-ended dsb are less damaging than blunt-ended dsb. Multiple fixation time experiments showed that the higher sensitivity of xrs 5 was evident at several different sampling times after treatment. Similarly the low yield of aberrations after exposure of cells to Bam H1 was evident at all sampling times. Overdispersion of chromosomal aberrations was observed in samples exposed to RE. This is thought to be due to a non-uniform permeabilization of the cell population to RE. Our results indicate that RE-induced dsb are handled by cells in a similar way to those arising during X-ray exposure.     

Isotopic differences in the lithium transport rate in human erythrocytes during simultaneous incubations with the stable isotopes 6Li and 7Li.

The membrane transport of the two stable lithium isotopes, 6Li and 7Li, by erythrocytes has been studied using a dual channel atomic absorption spectroscopic technique. 6Li appears to be taken up preferentially to 7Li, in the ratio of 10 to 40%, depending on the concentration of total lithium and on the lithium isotopic ratio in the external medium.     

Combination biotherapy utilizing interleukin-2 and alpha interferon in patients with advanced cancer: a National Biotherapy Study Group Trial.

The National Biotherapy Study Group (NBSG) conducted a broad phase II trial using interleukin-2 (IL-2) by continuous infusion and alpha interferon (IFN) subcutaneously in 267 patients with a variety of advanced cancers, including 29 with breast cancer, 89 with renal cancer, and 69 with melanoma. IL-2 [18 million international units (MIU)/m2] was given by continuous infusion for 108 hours with 3 mu/m2 subcutaneous IFN every other day during the IL-2 infusion. The patients were treated for 1 week followed by a 2-week rest. After two cycles of treatment, patients were evaluated for response. Of the 237 patients evaluable for response, 20 (8%) had a complete or partial response and 128 (54%) were stable. Therefore, 62% of the evaluable patients were nonprogressive during the first 90 days of IL-2/IFN therapy. The objective response rate was 11% in melanoma, 7% in renal cancer, 14% in breast cancer, and 3% in patients with a variety of malignancies for an overall response rate of 7% in these patients with advanced cancer. The patients were treated on a general medical ward and tolerated treatment well with fatigue and fever being nearly universal. Dyspnea, pruritus, chills, and elevated creatinines were frequent but less common. This combination biotherapy regimen has minimal activity in a variety of advanced cancers and must be compared with the best existing chemotherapy for each cancer type in randomized, prospective trials.     

Preliminary characterization of an antibiotic produced by Xanthomonas albilineans which inhibits DNA synthesis in Escherichia coli

Chlorosis-inducing isolates of Xanthomonas albilineans, the sugarcane leaf scald pathogen, produced a mixture of antibacterial compounds in culture. The antibiotic mixture, which eluted as a single strongly retarded peak from Sephadex LH-20 in methanol, was bactericidal to Escherichia coli. Inhibition of E. coli was not reversed by added nutrients, and affected cells were not lysed but many accumulated polyphosphate granules. The major antibacterial component, isolated in crystalline form after HPLC, is given the trivial name albicidin. Near the minimum inhibitory concentration, albicidin caused a complete block to DNA synthesis, followed by partial inhibition of RNA and protein synthesis, as assessed by incorporation of radioactive precursors. Spontaneous antibiotic-resistant mutants of E. coli showed no cross-resistance between albicidin and inhibitors of either subunit of DNA gyrase. Mixing albicidin with purified DNA from E. coli did not alter the thermal denaturation behaviour of the DNA, or the absorption spectrum of the antibiotic. PolA+ and PolA - strains of E. coli were equally sensitive to albicidin, indicating that the antibiotic does not bind to or modify DNA. Selective inhibition of DNA synthesis without evidence of DNA binding suggests a specific interaction of albicidin with an essential replication protein.     

Stable albicidin resistance in Escherichia coli involves an altered outer-membrane nucleoside uptake system

Albicidin blocked DNA synthesis in intact cells of a PolA- EndA- Escherichia coli strain, and in permeabilized cells supplied with all necessary precursor nucleotides, indicating a direct effect on prokaryote DNA replication. Replication of phages T4 and T7 was also blocked by albicidin in albicidin-sensitive (Albs) but not in albicidin-resistant (Albr) E. coli host-cells. All stable spontaneous Albr mutants of E. coli simultaneously became resistant to phage T6. The locus determining albicidin sensitivity mapped at tsx, the structural gene for an outer-membrane protein used as a receptor by phage T6 and involved in transport through the outer membrane of nucleosides present at submicromolar extracellular concentrations. Albicidin does not closely resemble a nucleoside in structure. However, Albs E. coli strains rapidly accumulated both nucleosides and albicidin from the surrounding medium whereas the Albr mutants were defective in uptake of nucleosides and albicidin at low extracellular concentrations. An insertion mutation blocking Tsx protein production also blocked albicidin uptake and conveyed albicidin resistance. Albicidin supplied at approximately 0.1 microM blocked DNA replication within seconds in intact Albs E. coli cells, but a 100-fold higher albicidin concentration was necessary for a rapid inhibition of DNA replication in permeabilized cells. We conclude that albicidin is effective at very low concentrations against E. coli because it is rapidly concentrated within cells by illicit transport through the tsx-encoded outer-membrane channel normally involved in nucleoside uptake. Albicidin resistance results from loss of the mechanism of albicidin transport through the outer membrane.     

Calcium influences the stability and conformation of rotavirus SAH glycoprotein VP7 expressed in Dictyostelium discoideum

We have previously reported expression of the rotavirus outer capsid glycoprotein, VP7, in the relatively new expression host, Dictyostelium discoideum. To optimise yields of recombinant VP7, we examined the role of Ca²⁺ since stability of both VP7 and mature rotavirus during a rotavirus infection are calcium-dependent. Low micromolar levels of free extracellular Ca²⁺ were required to maximise yields of VP7 in D. discoideum whilst levels of VP7 were reduced following depletion of intracellular Ca²⁺ reserves using A23187 and EGTA. Immunoblot analysis suggested that VP7 was being degraded in an intracellular compartment. Immunoprecipitation with a conformation-dependent neutralising antibody confirmed that EGTA-induced Ca²⁺ chelation alters the conformation of VP7. These results suggest that stability of VP7 is dependent on maintaining adequate levels of intracellular Ca²⁺ and that conformational changes in VP7 which occur following depletion of Ca²⁺ reserves induce rapid proteolysis of the protein. Since these results establish conditions for expressing optimal levels of VP7 in the correct conformation they have important implications for the development of a subunit vaccine based on recombinant VP7.