Comparative radiation tolerance based on the induction of DNA double-strand breaks in tobacco BY-2 cells and CHO-K1 cells irradiated with gamma rays

Higher plants are generally more tolerant to ionizing radiation than mammals. To explore the radiation tolerance of higher plants, the induction of DNA double-strand breaks (DSBs) by gamma rays was investigated in tobacco BY-2 cells and compared with that in Chinese hamster ovary (CHO)-K1 cells as a reference. This is the first examination of radiation-induced DSBs in a higher plant cell. The resulting DNA fragments were separated by pulsed-field gel electrophoresis and stained with SYBR Green I. The initial yield of DSBs was then quantified from the fraction of DNA fragments shorter than 1.6 Mbp based on the assumption of random distribution of DSBs. The DSB yield in tobacco BY-2 cells (2.0 +/- 0.1 DSBs Gbp(-1) Gy(-1)) was only one-third of that in CHO-K1 cells. Furthermore, the calculated number of DSBs per diploid cell irradiated with gamma rays at the mean lethal dose was five times greater in BY-2 cells (263 +/- 13) than in CHO-K1 cells. These results suggest that the radiation tolerance of BY-2 cells appears to be due not only to a lower induction of DNA damage but also to a more efficient repair of the induced DNA damage.     

Potent anti-R5 human immunodeficiency virus type 1 effects of a CCR5 antagonist, AK602/ONO4128/GW873140, in a novel human peripheral blood mononuclear cell nonobese diabetic-SCID, interleukin-2 receptor gamma-chain-knocked-out AIDS mouse model

We established human peripheral blood mononuclear cell (PBMC)-transplanted R5 human immunodeficiency virus type 1 isolate JR-FL (HIV-1(JR-FL))-infected, nonobese diabetic-SCID, interleukin 2 receptor gamma-chain-knocked-out (NOG) mice, in which massive and systemic HIV-1 infection occurred. The susceptibility of the implanted PBMC to the infectivity and cytopathic effect of R5 HIV-1 appeared to stem from hyperactivation of the PBMC, which rapidly proliferated and expressed high levels of CCR5. When a novel spirodiketopiperazine-containing CCR5 inhibitor, AK602/ONO4128/GW873140 (molecular weight, 614), was administered to the NOG mice 1 day after R5 HIV-1 inoculation, the replication and cytopathic effects of R5 HIV-1 were significantly suppressed. In saline-treated mice (n = 7), the mean human CD4(+)/CD8(+) cell ratio was 0.1 on day 16 after inoculation, while levels in mice (n = 8) administered AK602 had a mean value of 0.92, comparable to levels in uninfected mice (n = 7). The mean number of HIV-RNA copies in plasma in saline-treated mice were approximately 10(6)/ml on day 16, while levels in AK602-treated mice were 1.27 x 10(3)/ml (P = 0.001). AK602 also significantly suppressed the number of proviral DNA copies and serum p24 levels (P = 0.001). These data suggest that the present NOG mouse system should serve as a small-animal AIDS model and warrant that AK602 be further developed as a potential therapeutic for HIV-1 infection.     

Emission mechanism of floral scent in Petunia axillaris

The mechanism of floral scent emission was studied in Petunia axillaris, a plant with a diurnal rhythm of scent output. The emission rate of each volatile compound oscillated in synchrony with its endogenous concentration, so that the intensity of the floral scent appeared to be determined by the endogenous concentrations. The composition of major volatiles in the flower tissue and the flower headspace showed characteristic differences. A negative correlation was found between the boiling points of the volatile compounds and the ratio of their emitted and endogenous concentrations, indicating that the composition of the floral scent depends directly on the endogenous composition of the volatile compounds. We conclude that in P. axillaris, the physiological regulation of floral scent emission operates not in the vaporization process but in the control of the endogenous concentrations of volatiles through biosynthesis and metabolic conversion.     

The hypervariable domain of the mitochondrial control region in Atlantic spiny lobsters and its potential as a marker for investigating phylogeographic structuring

Atlantic spiny lobsters support major fisheries in northeastern Brazilian waters and in the Caribbean Sea. To avoid reduction in diversity and elimination of distinct stocks, understanding their population dynamics, including structuring of populations and genetic diversity, is critical. We here explore the potential of using the hypervariable domain in the control region of the mitochondrial DNA as a genetic marker to characterize population subdivision in spiny lobsters, using Panulirus argus as the species model. The primers designed on the neighboring conserved genes have amplified the entire control region (approx. 780 bases) of P. argus and other closely related species. Average nucleotide and haplotype diversity within P. argus were found to be high, and population structuring was hypothesized. The data suggest a division of P. argus into genetically different phylogeographic groups. The hypervariable domain seems to be useful for determining genetic differentiation of geographically distinct stocks of P. argus and other Atlantic spiny lobsters.     

Rescue of abnormal phenotypes of the delta2 glutamate receptor-null mice by mutant delta2 transgenes

The delta2 glutamate receptor (GluRdelta2) has a crucial role in cerebellar functions; disruption of GluRdelta2 alleles in mice (delta2(-/-)) impairs synapse formation and long-term depression, which is thought to underlie motor learning in the cerebellum, and consequently leads to motor discoordination. However, it has been unclear whether GluRdelta2 is activated by glutamate analogues. Here we introduced a GluRdelta2 transgene, which had a mutation (Arg514Lys) in the putative ligand-binding motif conserved in all mammalian ionotropic glutamate receptors (iGluRs) and their ancestral bacterial periplasmic amino-acid-binding proteins, into delta2(-/-) mice. Surprisingly, a mutant GluRdelta2 transgene, as well as a wild-type GluRdelta2 transgene, rescued all abnormal phenotypes of delta2(-/-) mice. Therefore, these results indicate that the conserved arginine residue, which is crucial for the binding of iGluRs to glutamate analogues, is not essential for the restoration of GluRdelta2 functions in delta2(-/-) mice.     

Light-induced global structural changes in phytochrome A regulating photomorphogenesis in plants

Phytochromes are photoreceptor proteins that monitor the light environment and regulate a variety of photomorphogenic responses to optimize the growth and development of plants. Phytochromes comprise N-terminal photosensory and C-terminal regulatory domains. They are mutually photoconvertible between a red-light-absorbing (Pr) and a far-red-light-absorbing (Pfr) form. Their interconversion by light stimuli initiates downstream signaling cascades. Here we report the molecular structures of pea phytochrome A lacking the N-terminal 52 amino-acid residues in the Pr and Pfr forms studied by small-angle X-ray scattering. A new purification protocol yielded monodispersive sample solutions. The molecular mass and the maximum dimension of Pr determined from scattering data indicated its dimeric association. The molecular structure of Pr predicted by applying the ab initio simulation method to the scattering profile was approximated as a stack of two flat bodies, comprising two lobes assignable to the functional regions. Scattering profiles recorded under red-light irradiation showed small but definite changes from those of Pr. The molecular dimensions and predicted molecular structure of Pfr suggest global structural changes such as movement of the C-terminal domains in the Pr-to-Pfr phototransformation. Red-light-induced structural changes in Pfr were reversible, mostly due to thermal relaxation processes.