Schizosaccharomyces pombe switches mating type by the synthesis-dependent strand-annealing mechanism

Schizosaccharomyces pombe cells can switch between two mating types, plus (P) and minus (M). The change in cell type occurs due to a replication-coupled recombination event that transfers genetic information from one of the silent-donor loci, mat2P or mat3M, into the expressed mating-type determining mat1 locus. The mat1 locus can as a consequence contain DNA encoding either P or M information. A molecular mechanism, known as synthesis-dependent strand annealing, has been proposed for the underlying recombination event. A key feature of this model is that only one DNA strand of the donor locus provides the information that is copied into the mat1. Here we test the model by constructing strains that switch using two different mutant P cassettes introduced at the donor loci, mat2 and mat3. We show that in such strains wild-type P-cassette DNA is efficiently generated at mat1 through heteroduplex DNA formation and repair. The present data provide an in vivo genetic test of the proposed molecular recombination mechanism.     

Lipopolysaccharide enhances the production of nicotine-induced prostaglandin E2 by an increase in cyclooxygenase-2 expression in osteoblasts

Previous studies have indicated that lipopolysaccharide(LPS)from Gram-negative bacteria inplaque induces the release of prostaglandin E_2(PGE_2),which promotes alveolar bone resorption in periodontitis,and that tobacco smoking might be an important risk factor for the development and severity of periodontitis.We determined the effect of nicotine and LPS on alkaline phosphatase(ALPase)activity,PGE_2 production,and the expression of cyclooxygenase(COX-1,COX-2),PGE_2 receptors Ep1-4,and macrophage colonystimulating factor(M-CSF)in human osteoblastic Saos-2 cells.The cells were cultured with 10~(-3)M nicotinein the presence of 0,1,or 10μg/ml LPS,or with LPS alone.ALPase activity decreased in cells cultured withnicotine or LPS alone,and decreased further in those cultured with both nicotine and LPS,whereas PGE_2production significantly increased in the former and increased further in the latter.By itself,nicotine did notaffect expression of COX-1,COX-2,any of the PGE_2 receptors,or M-CSF,but when both nicotine and LPSwere present,expression of COX-2,Ep3,Ep4,and M-CSF increased significantly.Simultaneous addition of10~(-4)M indomethacin eliminated the effects of nicotine and LPS on ALPase activity,PGE_2 production,and M-CSF expression.Phosphorylation of protein kinase A was high in cells cultured with nicotine and LPS.Theseresults suggest that LPS enhances the production of nicotine-induced PGE_2 by an increase in COX-2 expres-sion in osteoblasts,that nicotine-LPS-induced PGE_2 interacts with the osteoblast Ep4 receptor primarily inautocrine or paracrine mode,and that the nicotine-LPS-induced PGE_2 then decreases ALPase activity andincreases M-CSF expression.     

DNA adenine methylation changes dramatically during establishment of symbiosis

The DNA adenine methylation status on specific 5'-GANTC-3' sites and its change during the establishment of plant-microbe interactions was demonstrated in several species of alpha-proteobacteria. Restriction landmark genome scanning (RLGS), which is a high-resolution two dimensional DNA electrophoresis method, was used to monitor the genomewide change in methylation. In the case of Mesorhizobium loti MAFF303099, real RLGS images obtained with the restriction enzyme MboI, which digests at GATC sites, almost perfectly matched the virtual RLGS images generated based on genome sequences. However, only a few spots were observed when the restriction enzyme HinfI was used, suggesting that most GANTC (HinfI) sites were tightly methylated and specific sites were unmethylated. DNA gel blot analysis with the cloned specifically unmethylated regions (SUMs) showed that some SUMs were methylated differentially in bacteroids compared to free-living bacteria. SUMs have also been identified in other symbiotic and parasitic bacteria. These results suggest that DNA adenine methylation may contribute to the establishment and/or maintenance of symbiotic and parasitic relationships.     

Retrotransposon silencing by DNA methylation can drive mammalian genomic imprinting

Among mammals, only eutherians and marsupials are viviparous and have genomic imprinting that leads to parent-of-origin-specific differential gene expression. We used comparative analysis to investigate the origin of genomic imprinting in mammals. PEG10 (paternally expressed 10) is a retrotransposon-derived imprinted gene that has an essential role for the formation of the placenta of the mouse. Here, we show that an orthologue of PEG10 exists in another therian mammal, the marsupial tammar wallaby (Macropus eugenii), but not in a prototherian mammal, the egg-laying platypus (Ornithorhynchus anatinus), suggesting its close relationship to the origin of placentation in therian mammals. We have discovered a hitherto missing link of the imprinting mechanism between eutherians and marsupials because tammar PEG10 is the first example of a differentially methylated region (DMR) associated with genomic imprinting in marsupials. Surprisingly, the marsupial DMR was strictly limited to the 5′ region of PEG10, unlike the eutherian DMR, which covers the promoter regions of both PEG10 and the adjacent imprinted gene SGCE. These results not only demonstrate a common origin of the DMR-associated imprinting mechanism in therian mammals but provide the first demonstration that DMR-associated genomic imprinting in eutherians can originate from the repression of exogenous DNA sequences and/or retrotransposons by DNA methylation.     

8-Oxoguanosine and uracil repair of nuclear and mitochondrial DNA in red and white skeletal muscle of exercise-trained old rats.

Oxoguanine DNA glycosylase (OGG1) and uracil DNA glycosylase (UDG) are two of the most important repair enzymes that are involved in the base excision repair processes to eliminate oxidative damage from mammalian DNA, which accumulates with aging. Red and white skeletal muscle fibers have very different antioxidant enzyme activities and resistance to oxidative stress. In this paper, we demonstrate that the activity of OGG1 is significantly higher in the red type of skeletal muscle compared with white fibers from old rats. Exercise training resulted in increased OGG1 activity in the nuclei of red fibers and decreased activity in nuclei of white fibers and in the mitochondria of both red and white fibers. The activities of UDG were similar in both red and white muscle fibers. Exercise training appears to increase the activity of UDG in the nuclei and mitochondria. However, exercise training affects the activity of OGG1 in nuclei and mitochondria differently, suggesting different regulation of the enzymes. In contrast, UDG showed similar activities in nuclei and mitochondrial extracts of exercise-trained animals. These data provide evidence for differential regulation of UDG and OGG1 in maintaining fidelity of DNA in oxidatively stressed cells.     

Chromosome-Scale Genome Assembly of the Marine Oleaginous Diatom Fistulifera solaris

Marine Biotechnology - Microalgae including diatoms are of interest for environmentally friendly manufacturing such as production of biofuels, chemicals, and materials. The highly oil-accumulating...     

Correction to: Why is chlorophyll b only used in light-harvesting systems?

Journal of Plant Research - The article Why is chlorophyll b only used in light-harvesting systems.     

Population structure and dynamics of an evergreen shade herb, Ainsliaea apiculata (Asteraceae), with special reference to herbivore effects

The population structure and dynamics of Ainsliaea apiculata, a forest understory evergreen herb widely distributed in Japan, was examined in a Chamaecyparis obtusa forest in Ibaraki Prefecture, central Japan (36°51N, 140°33E; 750 m a.s.l.). The mean population growth rate () calculated from the transition matrices for 4 years was 0.69 per year, predicting that the population size will decrease remarkably. There was a significant positive correlation between the survival of old leaves and the growth of new shoots in the following year. The shoots, especially new leaves, were damaged severely by herbivores (caterpillars of Leioptilus sp.). The survival rate of leaves formed in the previous spring to the next spring was remarkably low (41–54%). The growth of new shoots depended mainly on the reserves contained in old shoots, especially those in old leaves. New shoots of A. apiculata began to develop in spring, even though they were formed in autumn of the previous year. A defoliation experiment also showed that the removal of old shoots at the beginning of the growing season significantly inhibited the growth of new shoots. Damage to old shoots by herbivores severely influenced the growth and population dynamics of A. apiculata.