Reduced canine BRCA2 expression levels in mammary gland tumors.

BACKGROUND: Mammary tumors are the most common tumor type in intact female dogs. Recently, the breast cancer 2 early onset (BRCA2) gene was proposed to be associated with tumorigenesis in dogs. The expression level of BRCA2 is important for its DNA repair function in mammalian cells, and its expression level is linked to tumorigenesis in mammary tissue. However, the expression of canine BRCA2 in mammary tumors is unclear. RESULTS: BRCA2 mRNA levels were compared between seven mammary gland samples and seventeen mammary tumor samples isolated from dogs. The expression level of canine BRCA2 in mammary tumor samples was lower than levels in mammary gland samples. We attempted to identify why the BRCA2 expression level was decreased in mammary tumor samples by promoter sequencing analysis; however, we did not find any mutations in the canine BRCA2 promoter that altered BRCA2 transcription levels. We did detect two types of BRCA2 splice variants in 8 mammary tumor samples. One of the variants induced a frame-shift mutation that could lead to nonsense-mediated mRNA decay, a ubiquitous cellular mechanism that eliminates mRNA containing a premature termination codon. CONCLUSIONS: Reduced expression of canine BRCA2 mRNA in mammary tumor samples is a possible mechanism to explain mammary tumor development in dogs. One possible reason for reduced BRCA2 mRNA levels in these tumor samples was nonsense-mediated mRNA decay, not mutations in the BRCA2 promoter region. While it remains unclear why canine BRCA2 expression levels are reduced in mammary tumor samples, this study found that the expression level of BRCA2 was associated with canine mammary tumorigenesis.

Granular cell tumor of the brachial nerve in a dog: A case report.

Here, we describe the first case of a granular cell tumor (GCT) derived from the brachial nerve. Eleven-year-old neutered female Chihuahua presented to the hospital with a bulge from the left neck to the axilla. The dog had a spherical subcutaneous mass on the cervical subcutis, and cytology hinted at adenocarcinoma or neuroendocrine tumor. However, the origin of the tumor remains unknown. During resection of the mass, bleeding was difficult to control owing to the high blood flow, and tumor removal was extremely difficult. The caudal aspect of the mass was attached to the brachial nerve and had to be removed, along with parts of the nerve fibers. The patient's postoperative course was fair, but it developed paralysis of the left thoracic limb. Pathology revealed that the mass was positive for S100 and vimentin, and GCT was diagnosed. Non-oral GCTs are extremely rare. The clinical diagnosis of GCT is difficult and is often confirmed histopathologically by excision. Although most cases of GCT are benign, they must be recognized as hemorrhagic, indistinct masses that mimic malignancy. Excision carries the risk of hemorrhage and damage to the surrounding tissues to secure margins.

Descrevemos aqui o primeiro caso de um tumor de células granulares (TCG) derivado do nervo braquial. Uma chihuahua castrada de 11 anos de idade deu entrada no hospital com uma protuberância do pescoço esquerdo até a axila. A cadela apresentava uma massa subcutânea esférica no subcutâneo cervical, e a citologia indicava adenocarcinoma ou tumor neuroendócrino. Entretanto, a origem do tumor permanece desconhecida. Durante a ressecção da massa, foi difícil controlar o sangramento devido ao alto fluxo sanguíneo, e a remoção do tumor foi difícil. O aspecto caudal da massa estava ligado ao nervo braquial e teve de ser removido, juntamente com partes das fibras nervosas. A evolução pós-operatória da paciente foi regular, mas ele desenvolveu paralisia do membro torácico esquerdo. O exame anatomopatológico revelou que a massa era positiva para S100 e vimentina, e o TCG foi diagnosticado. Os TCGs não orais são extremamente raros. O diagnóstico clínico do TCG é difícil e geralmente é confirmado histopatologicamente por excisão. Embora a maioria dos casos de TCG seja benigna, eles devem ser reconhecidos como massas hemorrágicas e indistintas que simulam malignidade. A excisão acarreta o risco de hemorragia e danos aos tecidos circundantes para garantir as margens.

Ionising irradiation alters the dynamics of human long interspersed nuclear elements 1 (LINE1) retrotransposon.

It is important to identify the mechanism by which ionising irradiation induces various genomic alterations in the progeny of surviving cells. Ionising irradiation activates mobile elements like retrotransposons, although the mechanism of its phenomena consisting of transcriptions and insertions of the products into new sites of the genome remains unclear. In this study, we analysed the effects of sparsely ionising X-rays and densely ionising carbon-ion beams on the activities of a family of active retrotransposons, long interspersed nuclear elements 1 (L1). We used the L1/reporter knock-in human glioma cell line, NP-2/L1RP-enhanced GFP (EGFP), that harbours full-length L1 tagged with EGFP retrotransposition detection cassette (L1RP-EGFP) in the chromosomal DNA. X-rays and carbon-ion beams similarly increased frequencies the transcription from L1RP-EGFP and its retrotransposition. Short-sized de novo L1RP-EGFP insertions with 5'-truncation were induced by X-rays, while full-length or long-sized insertions (>5 kb, containing ORF1 and ORF2) were found only in cell clones irradiated by the carbon-ion beams. These data suggest that X-rays and carbon-ion beams induce different length of de novo L1 insertions, respectively. Our findings thus highlight the necessity to investigate the mechanisms of mutations caused by transposable elements by ionising irradiation.

Kinetic analysis of double-strand break rejoining reveals the DNA reparability of gamma-irradiated tobacco cultured cells.

The rejoining efficiency of double-strand breaks (DSBs) was quantified by a DNA fragment-size analysis in tobacco protoplasts and CHO-K1 cells following gamma-ray irradiation in order to compare DNA reparability of higher plants with mammals. Results showed that the DSB rejoining efficiency of tobacco protoplasts is dependent on the temperature of post-irradiation cultivation and that it reaches a maximum at 27 degrees C, which represents the most suitable temperature for protoplast cultivation. The DSB rejoining kinetics of tobacco protoplasts were well represented by a biphasic-exponential equation: half of initial-induced DSBs were rejoined for 1 h and the others were almost rejoined within 4 h. We found that the DSB rejoining kinetics of tobacco protoplasts at 27 degrees C are the same as those of CHO-K1 cells at 37 degrees C. These findings indicate that the DSB rejoining efficiency of tobacco protoplasts and CHO-K1 cells are comparable at their respective cell cultivation temperatures, suggesting that DSB rejoining efficiency is little responsible for the higher radiation-tolerance of tobacco protoplasts.

Targeted heavy-ion microbeam irradiation of the embryo but not yolk in the diapause-terminated egg of the silkworm, bombyx mori, induces the somatic mutation.

Using heavy-ion microbeam, we report target irradiation of selected compartments within the diapause-terminated egg and its mutational consequences in the silkworm, Bombyx mori. On one hand, carbon-ion exposure of embryo to 0.5-6 Gy increased the somatic mutation frequency, suggesting targeted radiation effects. On the other, such increases were not observed when yolk was targeted, suggesting a lack of nontargeted bystander effect.

LET dependence of the yield of single-, double-strand breaks and base lesions in fully hydrated plasmid DNA films by 4He(2+) ion irradiation.

PURPOSE: To characterize the complexity of DNA damage through determination of the yields of single (SSB) and double strand breaks (DSB), base lesions and clustered damage sites induced in fully hydrated plasmid DNA by direct radiation effects as a function of the ionizing density of the radiation using 4He(2+) ion irradiation with linear energy-transfer (LET) values in the range 19 to 148 keV/microm. MATERIALS AND METHODS: Hydrated plasmid DNA (pUC18) containing 34.5 water molecules/nucleotide was irradiated with He(2+) ions with LET values of 19, 63, 95, 121 and 148 keV/microm. From quantification of the conformational changes of the irradiated samples (closed circular, open or linear forms) analyzed by agarose gel electrophoresis, the yields of SSB and DSB were obtained. Base lesions were visualized as additional strand breaks by treatment with base excision repair enzymes (endonuclease III (Nth) and formamidpyrimidine DNA glycosylase (Fpg)). RESULTS: The yield of prompt SSB does not depend significantly on LET of the 4He(2+) ions, whereas the yield of prompt DSB increases with increasing LET. The yields of isolated base lesions, revealed by Nth and Fpg as additional SSB, decrease drastically with increasing LET. The sum of the yields of DSB and additional DSB revealed by Nth and Fpg increase with increasing LET of the 4He(2+) ions except at the highest LET investigated. CONCLUSION: The yields of clustered damage, revealed as DSB and non-DSB clustered damage sites, but not isolated lesions, namely SSB, increase with increasing ionization density of the 4He(2+) ions except at the highest LET investigated.

Heavy-ion microbeam system at JAEA-Takasaki for microbeam biology.

Research concerning cellular responses to low dose irradiation, radiation-induced bystander effects, and the biological track structure of charged particles has recently received particular attention in the field of radiation biology. Target irradiation employing a microbeam represents a useful means of advancing this research by obviating some of the disadvantages associated with the conventional irradiation strategies. The heavy-ion microbeam system at JAEA-Takasaki, which was planned in 1987 and started in the early 1990's, can provide target irradiation of heavy charged particles to biological material at atmospheric pressure using a minimum beam size 5 mum in diameter. A variety of biological material has been irradiated using this microbeam system including cultured mammalian and higher plant cells, isolated fibers of mouse skeletal muscle, silkworm (Bombyx mori) embryos and larvae, Arabidopsis thaliana roots, and the nematode Caenorhabditis elegans. The system can be applied to the investigation of mechanisms within biological organisms not only in the context of radiation biology, but also in the fields of general biology such as physiology, developmental biology and neurobiology, and should help to establish and contribute to the field of "microbeam biology".

Effects of locally targeted heavy-ion and laser microbeam on root hydrotropism in Arabidopsis thaliana.

Classical studies on root hydrotropism have hypothesized the importance of columella cells as well as the de novo gene expression, such as auxin-inducible gene, at the elongation zone in hydrotropism; however, there has been no confirmation that columella cells or auxin-mediated signaling in the elongation zone are necessary for hydrotropism. We examined the role of root cap and elongation zone cells in root hydrotropism using heavy-ion and laser microbeam. Heavy-ion microbeam irradiation of the elongation zone, but not that of the columella cells, significantly and temporarily suppressed the development of hydrotropic curvature. However, laser ablation confirmed that columella cells are indispensable for hydrotropism. Systemic heavy-ion broad-beam irradiation suppressed de novo expression of INDOLE ACETIC ACID 5 gene, but not MIZU-KUSSEI1 gene. Our results indicate that both the root cap and elongation zone have indispensable and functionally distinct roles in root hydrotropism, and that de novo gene expression might be required for hydrotropism in the elongation zone, but not in columella cells.

Heavy ion microbeam irradiation induces ultrastructural changes in isolated single fibers of skeletal muscle.

The effects of heavy ion microbeams on muscle fibers isolated from mouse skeletal muscles were examined by electron microscopy. The plasma membranes of heavy ion beam-irradiated areas of muscle fibers showed irregular protrusions and invaginations. In the cytoplasm, an irregular distribution of microfilaments was found near the plasma membrane. Sarcoplasmic reticula in the irradiated regions showed a distended appearance with flocculent material within the lumen. These changes were seen as early as 2 min after irradiation, and persisted until as late as 22 min after irradiation. Many autophagic vacuoles could be seen at 7 min after irradiation. At 22 min, the vacuoles became more prominent and showed more variety. These observations suggest that heavy ion beam irradiation causes disruption of the cellular architecture and the autophagy is involved in removal of this disruption.

Role of DNA-PKcs in the bystander effect after low- or high-LET irradiation.

PURPOSE: To investigate the role of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) in the medium-mediated bystander effect for chromosomal aberrations induced by low-linear energy transfer (LET) X-rays and high-LET heavy ions in normal human fibroblast cells. MATERIALS AND METHODS: The recipient cells were treated for 12 h with conditioned medium, which was harvested from donor cells at 24 h after exposure to 10 Gy of soft X-rays (5 keV/microm) and 20Ne ions (437 keV/microm), followed by analyses of chromosome aberrations in recipient cells with premature chromosome condensation methods. To examine the role of DNA-PKcs and nitric oxide (NO), cells were treated with its inhibitor LY294002 (LY) and its scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (c-PTIO), respectively. RESULTS: Increased frequency of chromosome aberrations in recipient cells treated with conditioned medium from irradiated but not from un-irradiated donor cells was observed which was independent of radiation type. Bystander induction of chromosome aberrations in recipient cells was mitigated when donor cells were treated with LY before irradiation and with c-PTIO after irradiation, and was enhanced when recipient cells were treated with LY before treatment of recipient cells with conditioned medium from irradiated donor cells. CONCLUSION: Irradiated normal human cells secrete NO and other molecules which in turn transmit radiation signals to unirradiated bystander cells, leading to the induction of bystander chromosome aberrations partially repairable by DNA-PKcs-mediated DNA damage repair machinery, such as non-homologous end-joining repair pathways.

Physiological changes leading to anhydrobiosis improve radiation tolerance in Polypedilum vanderplanki larvae.

High tolerance against various extreme environments exhibited by some anhydrobionts might be due to being almost completely desiccated, a state where little or no chemical reactions occur. We have shown that anhydrobiotic larvae of Polypedilum vanderplanki have higher tolerance against both high- and low-linear energy transfer (LET) radiation than hydrated larvae. It is of great interest to know how the desiccating larvae gain radiation tolerance. We therefore examined effects of high-LET radiation on four kinds of larvae: (1) normal hydrated (intact) larva, (2) intermediates between the anhydrobiotic and normal hydrated state, (3) almost completely dehydrated (anhydrobiotic) larvae, and (4) immediately rehydrated larvae that are assumed to have a similar molecular profile to anhydrobiotic larvae. The intermediates and immediately rehydrated larvae survived longer after high-LET radiation than intact larvae, indicating that radiation tolerance could be enhanced even in hydrated larvae. Physiological changes toward anhydrobiosis, e.g. accumulation of protectants or increasing damage repair capacity, correlate with improved radiation tolerance in hydrated larvae. In addition, almost complete desiccation further enhanced radiation tolerance, possibly in a different way from the hydrated larvae.

Development of the irradiation method for the first instar silkworm larvae using locally targeted heavy-ion microbeam.

To carry out the radio-microsurgery study using silkworm, Bombyx mori, we have already developed the specific irradiation systems for eggs and third to fifth instar larvae. In this study, a modified application consisting of the first instar silkworm larvae was further developed using heavy-ion microbeams. This system includes aluminum plates with holes specially designed to fix the first instar silkworm larvae during irradiation, and Mylar films were used to adjust energy deposited for planning radiation doses at certain depth. Using this system, the suppression of abnormal proliferation of epidermal cells in the knob mutant was examined. Following target irradiation of the knob-forming region at the first instar stage with 180-mum-diameter microbeam of 220 MeV carbon (12C) ions, larvae were reared to evaluate the effects of irradiation. The results indicated that the knob formation at the irradiated segment was specially suppressed in 5.9, 56.4, 66.7 and 73.6% of larvae irradiated with 120, 250, 400 and 600 Gy, respectively, but the other knob formations at the non-irradiated segments were not suppressed in either irradiation. Although some larva did not survive undesired non-targeted exposure, our present results indicate that this method would be useful to investigate the irradiation effect on a long developmental period of time. Moreover, our system could also be applied to other species by targeting tissues, or organs during development and metamorphosis in insect and animals.

Vulnerability of feline T-lymphocytes to charged particles.

An analysis of ionizing radiation-induced damage in peripheral lymphocytes has been employed to predict the prognosis of radiotherapy in terms of toxicity in normal tissues. Therefore, understanding the sensitivity of lymphocytes to high linear energy transfer (LET)-charged particles would be indispensable for utilizing charged particle therapy in veterinary medicine. However, the availability of such information is very limited. This study aimed to compare the radiosensitivity of feline T lymphocytes to gamma-rays (0.2 keV/microm) and 4 different types of charged particles with LET values ranging from 2.8 to 114 keV/microm. It was observed that the relative biological effectiveness, inactivation cross-section, and isodose-induced apoptosis increased in an LET-dependent manner. On the other hand, no difference in apoptosis frequency was observed in the cells exposed to an isosurvival dose of all the radiation types tested. This is the first study that demonstrates the LET dependence of cell killing and apoptosis induction in feline T lymphocytes. Our results suggest that lymphocytes can be effectively used to predict the prognosis of charged-particle therapy in cat patients.

Whole-Body Counter Evaluation of Internal Radioactive Cesium in Dogs and Cats Exposed to the Fukushima Nuclear Disaster.

As a result of the 2011 nuclear incident that occurred at the Fukushima Nuclear Power Plant, a large number of abandoned dogs and cats were left within the disaster zone. A small number of these animals were rescued and cared for at shelters. Prior to the dispersal of these animals to their owners or fosterers, we evaluated the degree of internal radiocesium contamination using a specially designed whole-body counter. We conducted 863 non-invasive measurements of gamma rays due to internal radioactive cesium for 68 dogs and 120 cats at one shelter. After plotting graphs of 137Cs density we generated exponential functions of decay from seven dogs and six cats. From the regression formulae, we were able to determine the biological half-lives as 38.2 days for dogs and 30.8 days for cats. We found that in dogs there was a correlation between the biological half-life of radioactive cesium and age. Using our data, we estimated whole-body densities for each cat and dog at the time when they were rescued. We found that there were deviations in the data distributions among the different species, likely due to the timing of rescue, or living habits prior to rescue. A significant correlation was found when extracted feline reproductive organs were analyzed; the coefficients for the estimation of whole-body densities were approximately 7-fold higher than those based on the extracted feline reproductive organs. This may be due to the fact that majority of the radioactive cesium accumulates within muscular tissue with less distribution in other organs. It is possible to plan the appropriate management period in an animal shelter based on the use of the biological half-life of radioactive cesium calculated in this study. We believe that the correlations we uncovered in this work would be of great use for the management of companion animals in the event of a future nuclear accident.

LET-dependent survival of irradiated normal human fibroblasts and their descendents.

Evidence has accumulated showing that ionizing radiations persistently perturb genomic stability and induce delayed reproductive death in the progeny of survivors; however, the linear energy transfer (LET) dependence of these inductions has not been fully characterized. We have investigated the cell killing effectiveness of gamma rays (0.2 keV/microm) and six different beams of heavy-ion particles with LETs ranging from 16.2 to 1610 keV/microm in normal human fibroblasts. First, irradiated confluent density-inhibited cultures were plated for primary colony formation, revealing that the relative biological effectiveness (RBE) based on the primary 10% survival dose peaked at 108 keV/microm and that the inactivation cross section increased proportionally up to 437 keV/microm. Second, cells harvested from primary colonies were plated for secondary colony formation, showing that delayed reproductive death occurred in a dose-dependent fashion. While the RBE based on the secondary 80% survival dose peaked at 108 keV/microm, very little difference in LET was observed in the RBE based on secondary survival at the primary 10% survival dose. Our present results indicate that delayed reproductive death arising only during secondary colony formation is independent of LET and is more likely to be dependent on initial damages having been fixed during primary colony formation.

Estimation of radiation tolerance to high LET heavy ions in an anhydrobiotic insect, Polypedilum vanderplanki.

PURPOSE: Anhydrobiotic larvae of Polypedilum vanderplanki are known to show an extremely high tolerance against a range of stresses. We have recently reported that this insect withstands exposure to high doses of gamma-rays (linear energy transfer [LET] 0.2 keV/microm). However, its tolerance against high LET radiation remains unknown. The aim of this study is to characterize the tolerance to high-LET radiations of P. vanderplanki. MATERIALS AND METHODS: Larval survival and subsequent metamorphoses were compared between anhydrobiotic (dry) and non-anhydrobiotic (wet) samples after exposure to 1 - 7000 Gy of three types of heavy ions delivered from the azimuthally varying field (AVF) cyclotron with LET values ranging from 16.2 - 321 keV/microm. The tolerance against 4He ions was also compared among three chironomid species. RESULTS: At all LET values measured, dry larvae consistently showed greater radiation tolerance than hydrated larvae, perhaps due to the presence of high concentrations of the disaccharide trehalose in anhydrobiotic animals, and the radiation-induced damage became evident at lower doses as development progressed. Relative biological effectiveness (RBE) values based on the median inhibitory doses reached a maximum at 116 keV/microm (12C), and the maximum RBE clearly increased as development progressed. Lower D0 (dose to reduce survival from relative value 1.00 - 0.37 on the exponential part of the survival curve), and higher Dq (quasi-threshold dose) were found in individuals exposed to 4He ions, compared to gamma-rays, and in P. vanderplanki larvae compared to non-anhydrobiotic chironomids. CONCLUSION: Anhydrobiosis potentiates radiation tolerance in terms of larval survival, pupation and adult emergence of P. vanderplanki exposed to high-LET radiations as well as to low-LET radiation. P. vanderplanki larvae might have more efficient DNA damage repair after radiation than other chironomid species.

Radiation tolerance in the tardigrade Milnesium tardigradum.

PURPOSE: Tardigrades are known to survive high doses of ionizing radiation. However, there have been no reports about radiation effects in tardigrades under culture conditions. In this study, we investigated tolerance of the tardigrade, Milnesium tardigradum, against gamma-rays and heavy ions by determining short-term or long-term survival, and reproductive ability after irradiation. MATERIALS AND METHODS: Hydrated and anhydrobiotic animals were exposed to gamma-rays (1000 - 7000 Gy) or heavy ions (1000 - 8000 Gy) to evaluate short-term survival at 2, 24 and 48 h post-irradiation. Long-term survival and reproduction were observed up to 31 days after irradiation with gamma-rays (1000 - 4000 Gy). RESULTS: At 48 h after irradiation, median lethal doses were 5000 Gy (gamma-rays) and 6200 Gy (heavy ions) in hydrated animals, and 4400 Gy (gamma-rays) and 5200 Gy (heavy ions) in anhydrobiotic ones. Gamma-irradiation shortened average life span in a dose-dependent manner both in hydrated and anhydrobiotic groups. No irradiated animals laid eggs with one exception in which a hydrated animal irradiated with 2000 Gy of gamma-rays laid 3 eggs, and those eggs failed to hatch, whereas eggs produced by non-irradiated animals hatched successfully. CONCLUSION: M. tardigradum survives high doses of ionizing radiation in both hydrated and anhydrobiotic states, but irradiation with >1000 Gy makes them sterile.

Biological effects of anhydrobiosis in an African chironomid, Polypedilum vanderplanki on radiation tolerance.

PURPOSE: Anhydrobiotic organisms are known to have an extremely high tolerance against a range of stresses. However, the functional role of anhydrobiosis in radiation tolerance is poorly understood, especially in development following irradiation. The present study aims to evaluate effects of anhydrobiosis on radiation tolerance in an anhydrobiotic insect, Polypedilum vanderplanki. MATERIALS AND METHODS: Larval survival (48 h), anhydrobiotic ability, metamorphosis and reproduction after exposure to 1-9000 Gy of gamma-rays at the larval stage were compared between anhydrobiotic (dry) and normal (wet) phases. RESULTS: Wet larvae were killed in a dose-dependent manner at doses higher than 2000 Gy, and all died within 8 h after 4000 Gy exposure. In contrast, dry larvae survived even 5000 Gy, and some of them still tolerated 7000 Gy and were alive at 48 h after rehydration. Moreover, greater radiotolerance of dry larva, compared to wet ones, was demonstrated in terms of metamorphoses. However, anhydrobiosis did not protect against radiation damage in terms of producing viable offspring. CONCLUSION: These results indicate that anhydrobiosis enhances radiotolerance, resulting in increases of successful metamorphoses.

Cell cycle arrest and apoptosis in Caenorhabditis elegans germline cells following heavy-ion microbeam irradiation.

PURPOSE: To investigate positional effects of radiation with an energetic heavy-ion microbeam on germline cells using an experimental model metazoan Caenorhabditis elegans. MATERIALS AND METHODS: The germline cells were irradiated with raster-scanned broad beam or collimated microbeam of 220 MeV 12C5+ particles delivered from the azimuthally varying field (AVF) cyclotron, and subsequently observed for cell cycle arrest and apoptosis. RESULTS: Whole-body irradiation with the broad beam at the L4 larval stage arrested germ cell proliferation. When the tip region of the gonad arm was irradiated locally with the microbeam at the L4 stage, the same arrest was observed. When the microbeams were used to irradiate the pachytene region of the gonad arm, at a young gravid stage, radiation-induced apoptosis occurred in the gonad. In contrast, arrest and apoptosis were not induced in the non-irradiated neighboring region or the opposite gonad. Similar results were confirmed in the c-abl-1 (mammalian ortholog of cellular counterpart of Abelson murine leukemia virus) mutant that is hypersensitive to radiation-induced apoptosis. CONCLUSION: These results indicate that the microbeam irradiation is useful in characterizing tissue-specific, local biological response to radiation in organisms. DNA damage-induced cell cycle arrest and apoptosis were observed in locally irradiated regions, but there was little, if any, 'bystander effect' in the nematode.

Method for detecting DNA strand breaks in mammalian cells using the Deinococcus radiodurans PprA protein.

In a previous study, we identified the novel protein PprA that plays a critical role in the radiation resistance of Deinococcus radiodurans. In this study, we focussed on the ability of PprA protein to recognize and bind to double-stranded DNA carrying strand breaks, and attempted to visualize radiation-induced DNA strand breaks in mammalian cultured cells by employing PprA protein using an immunofluorescence technique. Increased PprA protein binding to CHO-K1 nuclei immediately following irradiation suggests the protein is binding to DNA strand breaks. By altering the cell permeabilization conditions, PprA protein binding to CHO-K1 mitochondria, which is probably resulted from DNA strand break immediately following irradiation, was also detected. The method developed and detailed in this study will be useful in evaluating DNA damage responses in cultured cells, and could also be applicable to genotoxic tests in the environmental and pharmaceutical fields.