Extraordinarily low evolutionary rates of short wavelength-sensitive opsin pseudogenes

Aquatic organisms such as cichlids, coelacanths, seals, and cetaceans are active in UV–blue color environments, but many of them mysteriously lost their abilities to detect these colors. The loss of these functions is a consequence of the pseudogenization of their short wavelength-sensitive (SWS1) opsin genes without gene duplication. We show that the SWS1 gene (Bden_S1ψ) of the deep-sea fish, pearleye (Benthalbella dentata), became a pseudogene in a similar fashion about 130 million years ago (Mya) yet it is still transcribed. The rates of nucleotide substitution (~ 1.4 × 10^− 9/site/year) of the pseudogenes of these aquatic species as well as some prosimian and bat species are much smaller than the previous estimates for the globin and immunoglobulin pseudogenes.     

Loss of miRNA biogenesis induces p19Arf-p53 signaling and senescence in primary cells

Dicer, an enzyme involved in microRNA (miRNA) maturation, is required for proper cell differentiation and embryogenesis in mammals. Recent evidence indicates that Dicer and miRNA may also regulate tumorigenesis. To better characterize the role of miRNA in primary cell growth, we generated Dicer-conditional mice. Ablation of Dicer and loss of mature miRNAs in embryonic fibroblasts up-regulated p19(Arf) and p53 levels, inhibited cell proliferation, and induced a premature senescence phenotype that was also observed in vivo after Dicer ablation in the developing limb and in adult skin. Furthermore, deletion of the Ink4a/Arf or p53 locus could rescue fibroblasts from premature senescence induced by Dicer ablation. Although levels of Ras and Myc oncoproteins appeared unaltered, loss of Dicer resulted in increased DNA damage and p53 activity in these cells. These results reveal that loss of miRNA biogenesis activates a DNA damage checkpoint, up-regulates p19(Arf)-p53 signaling, and induces senescence in primary cells.     

Simulated environmental effects of wetland restoration scenarios in a typical Canadian prairie watershed

Wetland conservation and restoration contribute to improved watershed functions through providing both water quantity benefits in terms of flood attenuation and water quality benefits such as retention of sediment and nutrients. However, it is important to quantify these environmental benefits for informed decision making. This study uses a “hydrologic equivalent wetland” concept in the Soil and Water Assessment Tool to examine the effects of various wetland restoration scenarios on stream flow and sediment at a watershed scale. The modeling system was applied to the 25,139 ha Broughton’s Creek watershed in western Manitoba in Canada. As a representative prairie watershed, the Broughton’s Creek watershed experienced historic wetland losses from 2,998 ha in 1968 to 2,379 ha in 2005. Modeling results showed that if wetlands in the Broughton’s Creek watershed can be restored to the 1968 level, the peak discharge and average sediment loading can be reduced by 23.4 and 16.9%, respectively at the watershed outlet. Based on wetland and stream drainage areas estimated by the model and empirical nutrient export coefficients, the corresponding water quality benefits in terms of reductions in total phosphorus and nitrogen loadings were estimated at 23.4%. The modeling results are helpful for designing effective watershed restoration strategies in the Broughton’s Creek watershed. The developed methodology can be also applied to other study areas for examining the environmental effects of wetland restoration scenarios.     

Transformation of a psychrotrophic bacterium with a plasmid from a mesophile

The psychrotrophic bacteriumBacillus psychrophilus was transformed with the broadhost-range plasmid pC194. The ability of the transformant to express chloramphenicol (CAM) resistance and the possible effects of such expression on the physiology of the psychrotroph were examined. The transformant exhibited growth rates, filament formation at elevated temperatures, synthesis of cold shock proteins and cold acclimation proteins, similar to the parentalB. psychrophilus.     

Sources of spontaneous mutagenesis in bacteria

Mutations in an organism’s genome can arise spontaneously, that is, in the absence of exogenous stress and prior to selection. Mutations are often neutral or deleterious to individual fitness but can also provide genetic diversity driving evolution. Mutagenesis in bacteria contributes to the already serious and growing problem of antibiotic resistance. However, the negative impacts of spontaneous mutagenesis on human health are not limited to bacterial antibiotic resistance. Spontaneous mutations also underlie tumorigenesis and evolution of drug resistance. To better understand the causes of genetic change and how they may be manipulated in order to curb antibiotic resistance or the development of cancer, we must acquire a mechanistic understanding of the major sources of mutagenesis. Bacterial systems are particularly well-suited to studying mutagenesis because of their fast growth rate and the panoply of available experimental tools, but efforts to understand mutagenic mechanisms can be complicated by the experimental system employed. Here, we review our current understanding of mutagenic mechanisms in bacteria and describe the methods used to study mutagenesis in bacterial systems.     

Effects of methoprene and Bti (Bacillus thuringiensis var. israelenis) on non-target insects

The effects of mosquito larvicides Bacillus thuringiensis israelensis (Bti) and methoprene, on non-target benthic invertebrates were studied in a divided pond experiment in south-central Minnesota, USA, during the spring and summer of 1989. Density and biomass of insects and other benthic macroinvertebrates were quite low in all sections of the three ponds studied, which may have been due to three consecutive years of drought, but richness appeared to be high and we observed no evidence of dominance by a particular group. We also saw no evidence of negative effects of larvicide treatment on density or biomass of any invertebrate group, nor was there a treatment-related decrease in richness of benthic invertebrate taxa under these drought conditions.