Frequency of CD59 mutations induced in human-hamster hybrid A(L) cells by low-dose X-irradiation

Determination of the genotoxic effects of ionizing radiation, especially at low-doses, is of great importance for risk assessment, e.g. in radiological diagnostics. The human-hamster hybrid A(L) cell line has been shown previously to be a well-suited in vitro model for the study of mutations induced by various mutagens. The A(L) cells contain a standard set of hamster chromosomes and a single human chromosome 11, which confers the expression of the human cell surface protein CD59. Using CD59 specific antibodies, cells mutated in the CD59 gene can be detected and quantified by the loss of the cell surface marker. In contrast to previous studies, prior to irradiation we removed spontaneous mutants by magnetic cell separation (MACS) which allows analysis of radiation-induced mutation events only. We exposed A(L) cells to 100kV X-rays at 0.1 to 5Gy. The proportions of X-irradiation-induced CD59(-) mutants were quantified by flow cytometry after immunofluorescence labeling. Between 0.2 and 5Gy the yield of CD59 mutants was a linear function of dose. The molecular analysis of individual CD59-negative clones induced after exposure of 1, 3 and 5Gy of X-ray revealed a dose-dependent linear increase of large deletions (>6Mbp), whereas, point mutations could be seen only in spontaneous CD59 mutants or after low-dose exposure (< or =1Gy). We conclude that the modified A(L) assay presented here is appropriate for detection and quantification of non-lethal DNA lesions induced by low-dose ionizing radiation.     

Great tits (Parus major) flexibly learn that herbivore‐induced plant volatiles indicate prey location: An experimental evidence with two tree species

1. When searching for food, great tits (Parus major) can use herbivore‐induced plant volatiles (HIPVs) as an indicator of arthropod presence. Their ability to detect HIPVs was shown to be learned, and not innate, yet the flexibility and generalization of learning remain unclear.
2. We studied if, and if so how, naïve and trained great tits (Parus major) discriminate between herbivore‐induced and noninduced saplings of Scotch elm (Ulmus glabra) and cattley guava (Psidium cattleyanum). We chemically analyzed the used plants and showed that their HIPVs differed significantly and overlapped only in a few compounds.
3. Birds trained to discriminate between herbivore‐induced and noninduced saplings preferred the herbivore‐induced saplings of the plant species they were trained to. Naïve birds did not show any preferences. Our results indicate that the attraction of great tits to herbivore‐induced plants is not innate, rather it is a skill that can be acquired through learning, one tree species at a time.
4. We demonstrate that the ability to learn to associate HIPVs with food reward is flexible, expressed to both tested plant species, even if the plant species has not coevolved with the bird species (i.e., guava). Our results imply that the birds are not capable of generalizing HIPVs among tree species but suggest that they either learn to detect individual compounds or associate whole bouquets with food rewards.

     

Molecular recognition of DNA base pairs by the formamido/pyrrole and formamido/imidazole pairings in stacked polyamides

Polyamides containing an N-terminal formamido (f) group bind to the minor groove of DNA as staggered, antiparallel dimers in a sequence-specific manner. The formamido group increases the affinity and binding site size, and it promotes the molecules to stack in a staggered fashion thereby pairing itself with either a pyrrole (Py) or an imidazole (Im). There has not been a systematic study on the DNA recognition properties of the f/Py and f/Im terminal pairings. These pairings were analyzed here in the context of f-ImPyPy, f-ImPyIm, f-PyPyPy and f-PyPyIm, which contain the central pairing modes, –ImPy– and –PyPy–. The specificity of these triamides towards symmetrical recognition sites allowed for the f/Py and f/Im terminal pairings to be directly compared by SPR, CD and ΔT_M experiments. The f/Py pairing, when placed next to the –ImPy– or –PyPy– central pairings, prefers A/T and T/A base pairs to G/C base pairs, suggesting that f/Py has similar DNA recognition specificity to Py/Py. With –ImPy– central pairings, f/Im prefers C/G base pairs (>10 times) to the other Watson–Crick base pairs; therefore, f/Im behaves like the Py/Im pair. However, the f/Im pairing is not selective for the C/G base pair when placed next to the –PyPy– central pairings.