Relationship between cytotoxicity and induction of sister-chromatid exchanges in mouse foetal cells exposed to several doses of carcinogenic and non-carcinogenic chemicals.

The increase in sister-chromatid exchanges induced by 5 chemicals, with different DNA damaging and carcinogenic activities, was studied in short-term foetal-mouse cultures. A significant increase in SCE was induced by N-methyl-N'-nitro-N-nitrosoguanidine, N-diazoacetylglycine-amide, azaserine and methotrexate. k-Strophantin, on the contrary, was totally inactive. On a molar basis, MNNG was the most active chemical followed by MTX, AZS and DGA, in that order. At equitoxic concentrations (D37), the order of SCE-inducing abilities was MNNG, DGA, AZS and MTX. Compared with previous data, at equitoxic concentrations, the most DNA-damaging agents were also the most effective in inducing SCE. The SCE increase seems to correlate not with unspecific cytotoxicity but more with DNA damage or other damage at the genome level. MTX, a non-mutagen, which induced SCE only at toxic levels, could be considered a false positive because this positivity may reflect an enhancement of incorporation of 5-BrdUrd into DNA. The positive results obtained with AZS suggest a sufficient sensitivity of the method for detecting relatively weak carcinogens.     

DLC-1, a Rho GTPase-activating protein with tumor suppressor function, is essential for embryonic development

DLC-1 (deleted in liver cancer 1) is a Rho GTPase-activating protein that is able to inhibit cell growth and suppress tumorigenesis. We have used homologous recombination to inactivate the mouse DLC-1 gene (Arhgap7). Mice heterozygous for the targeted allele were phenotypically normal, but homozygous mutant embryos did not survive beyond 10.5 days post coitum. Histological analysis revealed that DLC-1-/- embryos had defects in the neural tube, brain, heart, and placenta. Cultured fibroblasts from DLC-1-deficient embryos displayed alterations in the organization of actin filaments and focal adhesions.     

An increase in the ATP levels occurs in cerebellar granule cells en route to apoptosis in which ATP derives from both oxidative phosphorylation and anaerobic glycolysis

Although it is recognized that ATP plays a part in apoptosis, whether and how its level changes en route to apoptosis as well as how ATP is synthesized has not been fully investigated. We have addressed these questions using cultured cerebellar granule cells. In particular, we measured the content of ATP, ADP, AMP, IMP, inosine, adenosine and l-lactate in cells undergoing apoptosis during the commitment phase (0-8 h) in the absence or presence of oligomycin or/and of citrate, which can inhibit totally the mitochondrial oxidative phosphorylation and largely the substrate-level phosphorylation in glycolysis, respectively. In the absence of inhibitors, apoptosis was accompanied by an increase in ATP and a decrease in ADP with 1:1 stoichiometry, with maximum ATP level found at 3 h apoptosis, but with no change in levels of AMP and its breakdown products and with a relatively low level of l-lactate production. Consistently, there was an increase in the cell energy charge and in the ratio ([ATP][AMP])/[ADP]². When the oxidative phosphorylation was completely blocked by oligomycin, a decrease of the ATP content was found both in control cells and in cells undergoing apoptosis, but nonetheless cells still died by apoptosis, as shown by checking DNA laddering and by death prevention due to actinomycin D. In this case, ATP was provided by anaerobic glycolysis, as suggested by the large increase of l-lactate production. On the other hand, citrate itself caused a small decrease in ATP level together with a huge decrease in l-lactate production, but it had no effect on cell survival. When ATP level was further decreased due to the presence of both oligomycin and citrate, death occurred via necrosis at 8 h, as shown by the lack of DNA laddering and by death prevention found due to the NMDA receptor antagonist MK801. However, at a longer time, when ATP level was further decreased, cells died neither via apoptosis nor via glutamate-dependent necrosis, in a manner similar to something like to energy catastrophe. Our results shows that cellular ATP content increases in cerebellar granule cell apoptosis, that the role of oxidative phosphorylation is facultative, i.e. ATP can also derive from anaerobic glycolysis, and that the type of cell death depends on the ATP availability.     

Tobamovirus-resistant tobacco generated by RNA interference directed against host genes

Two homologous Nicotiana tabacum genes NtTOM1 and NtTOM3 have been identified. These genes encode polypeptides with amino acid sequence similarity to Arabidopsis thaliana TOM1 and TOM3, which function in parallel to support tobamovirus multiplication. Simultaneous RNA interference against NtTOM1 and NtTOM3 in N. tabacum resulted in nearly complete inhibition of the multiplication of Tomato mosaic virus and other tobamoviruses, but did not affect plant growth or the ability of Cucumber mosaic virus to multiply. As TOM1 and TOM3 homologues are present in a variety of plant species, their inhibition via RNA interference should constitute a useful method for generating tobamovirus-resistant plants.     

The influence of temperature and habitat on the distribution of chiselmouth, Acrocheilus alutaceus, in British Columbia

We intensively sampled fish in rivers and streams within a single major drainage basin (the Blackwater River) and across major drainages in British Columbia to assess the factors influencing distribution of chiselmouth, Acrocheilus alutaceus, and to develop models for predicting chislemouth presence. Chiselmouth were typically absent from sites with maximum temperatures below 20°C or 2100 annual degree days, both within a single drainage and between larger drainages. Indices of stream size (bankfull channel width and basin area) were the most significant predictors of chiselmouth presence within the Blackwater drainage (p=0.016 and p=0.032, respectively), and inclusion of thermal variables only marginally increased classification success. In contrast, bankfull channel width and basin area were poor predictors of chiselmouth presence in mainstem habitat within larger drainage basins throughout British Columbia. Inclusion of thermal variables (particularly degree days > 12°C) doubled correct classification rates of chiselmouth presence across larger drainage basins. These habitat associations suggest that water temperature is the primary constraint on presence of chiselmouth populations in larger drainages across a landscape, while selection of different habitat types (mainstem habitat over smaller tributaries) determines distribution within any given basin.     

Effect of Indian mustard on feeding,larval survival and development of Plutella xylostella at constant temperatures

Feeding behavior of Plutella xylostella under optional to non-optional conditions was studied at 10°C, 15°C, 20°C, and 25°C on Indian mustard, Brassica juncea. The study reveals that the variety Pusa Bahar was significantly less preferred by the larvae as compared with Pusa Bold and Varuna under optional to non-optional conditions. Larvae of P. xylostella consumed more food at 25°C than 20°C, 15°C and 10°C. Larval survival was found to be highest on cabbage (control) as compared with Indian mustard and was found to vary with host plants and temperature. The larval survival decreased to 11.29% on Pusa Bahar at 10°C. Increasing the temperature from 10°C to 20°C, larval mortality resulted more on Varuna than Pusa Bahar and Pusa Bold. Developmental period was prolonged on Pusa Bold at 10°C while it was shortest on cabbage at 25°C. A total of 536.47 degree days were required to complete the development by immature stages on Varuna at 25°C and 421.64 degree days on cabbage.     

Growing degree days – Ecosystem indicator for changing diurnal temperatures and their impact on corn growth stages in Kansas

Understanding how climate change will affect plant phenology (shifts in the timing of plant activity) is central to many ecological and biogeochemical studies. This aspect of plant ecology often has been overlooked, but addressing the consequences of climate change for adaptive/mitigative management is now high on the list of priorities for funding agencies. This study is innovative because it uses growing degree days (GDD), which has existed since the 1730s, as an ecosystem indicator to study changing diurnal temperatures; their effects on different plant growth stages in the last century; and as a basis for development of future adaptive management strategies. Our results show the most recent time period (1980–2009) had the earliest emergence and the least variability among stations in the day at which the crop stage occurred for most stages except emergence and physiological maturity. 100 year linear trends in the stations indicated all seven crop stages except tassel initiation occurred earlier by one day per decade during the study period. The number of stations with significant decreases varied from 11 to 17 stations out of 23 stations in Kansas. Tassel initiation stage occurred later by one day per decade during the study period. The most recent time period (1980–2009) had the highest variability among stations and 30 year time periods. The variability in trends is higher in western Kansas when compared to eastern Kansas. This knowledge has transformative potential to improve our understanding of the occurrence and duration of the different plant growth stages, add local precision to earlier findings for changes in overall GDD that encompassed larger areas, and help explain the differences in trends from some earlier studies. These shifts in the phenology of agricultural plants as a result of climate change have implications on food production increases required to feed the growing population.     

Wnt-5a increases NO and modulates NMDA receptor in rat hippocampal neurons

Wnt signaling has a crucial role in synaptic function at the central nervous system. Here we evaluate whether Wnts affect nitric oxide (NO) generation in hippocampal neurons. We found that non-canonical Wnt-5a triggers NO production; however, Wnt-3a a canonical ligand did not exert the same effect. Co-administration of Wnt-5a with the soluble Frizzled related protein-2 (sFRP-2) a Wnt antagonist blocked the NO production. Wnt-5a activates the non-canonical Wnt/Ca²⁺ signaling through a mechanism that depends on Ca²⁺ release from Ryanodine-sensitive internal stores. The increase in NO levels evoked by Wnt-5a promotes the insertion of the GluN2B subunit of the NMDA receptor (NMDAR) into the neuronal cell surface. To the best of our knowledge, this is the first time that Wnt-5a signaling is related to NO production, which in turn increases NMDARs trafficking to the cell surface.     

Mountain goat survival in coastal Alaska: Effects of age,sex, and climate

Ecological theory predicts that individual survival should vary between sex and age categories due to differences in allocation of nutritional resources for growth and reproductive activities. During periods of environmental stress, such relationships may be exacerbated, and affect sex and age classes differently. We evaluated support for hypotheses about the relative roles of sex, age, and winter and summer climate on the probability of mountain goat (Oreamnos americanus) survival in coastal Alaska. Specifically, we used known-fates analyses (Program MARK) to model the effects of age, sex, and climatic variation on survival using data collected from 279 radio-marked mountain goats (118 M, 161 F) in 9 separate study areas during 1977–2008. Models including age, sex, winter snowfall, and average daily summer temperature (during Jul–Aug) best explained variation in survival probability of mountain goats. Specifically, our findings revealed that old animals (9+ yr) have lower survival than younger animals. In addition, males tended to have lower survival than females, though differences only existed among prime-aged adult (5–8 yr) and old (9+ yr) age classes. Winter climate exerted the strongest effects on mountain goat survival; summer climate, however, was significant and principally influenced survival during the following winter via indirect effects. Furthermore, old animals were more sensitive to the effects of winter conditions than young or prime-aged animals. These findings detail how climate interacts with sex and age characteristics to affect mountain goat survival. Critically, we provide baseline survival rate statistics across various age, sex, and climate scenarios. These data will assist conservation and management of mountain goats by enabling detailed, model-based demographic forecasting of human and/or climate-based population impacts. © 2011 The Wildlife Society.