Developmental profiles of PERIOD and DOUBLETIME in Drosophila melanogaster ovary

The clock protein PERIOD (PER) displays circadian cycles of accumulation, phosphorylation, nuclear translocation and degradation in Drosophila melanogaster clock cells. One exception to this pattern is in follicular cells enclosing previtellogenic ovarian egg chambers. In these cells, PER remains high and cytoplasmic at all times of day. Genetic evidence suggest that PER and its clock partner TIMELESS (TIM) interact in these cells, yet, they do not translocate to the nucleus. Here, we investigated the levels and subcellular localization of PER in older vitellogenic follicles. Cytoplasmic PER levels decreased in the follicular cells at the onset of vitellogenesis (stage 9). Interestingly, PER was observed in the nuclei of some follicular cells at this stage. PER signal disappeared in more advanced (stage 10) vitellogenic follicles. Since the phosphorylation state of PER is critical for the progression of circadian cycle, we investigated the status of PER phosphorylation in the ovary and the expression patterns of DOUBLETIME (DBT), a kinase known to affect PER in the clock cells. DBT was absent in previtellogenic follicular cells, but present in the cytoplasm of some stage 9 follicular cells. DBT was not distributed uniformly but was present in patches of adjacent cells, in a pattern resembling PER distribution at the same stage. Our data suggest that the absence of dbt expression in the follicular cells of previtellogenic egg chambers may be related to stable and cytoplasmic expression of PER in these cells. Onset of dbt expression in vitellogenic follicles coincides with nuclear localization of PER protein.     

Genetic inactivation of NPC1L1 protects against sitosterolemia in mice lacking ABCG5/ABCG8

Mice lacking Niemann-Pick C1-Like 1 (NPC1L1) (NPC1L1(-/-)mice) exhibit a defect in intestinal absorption of cholesterol and phytosterols. However, wild-type (WT) mice do not efficiently absorb and accumulate phytosterols either. Cell-based studies show that NPC1L1 is a much weaker transporter for phytosterols than cholesterol. In this study, we examined the role of NPC1L1 in phytosterol and cholesterol trafficking in mice lacking ATP-binding cassette (ABC) transporters G5 and G8 (G5/G8(-/-) mice). G5/G8(-/-) mice develop sitosterolemia, a genetic disorder characterized by the accumulation of phytosterols in blood and tissues. We found that mice lacking ABCG5/G8 and NPC1L1 [triple knockout (TKO) mice] did not accumulate phytosterols in plasma and the liver. TKO mice, like G5/G8(-/-) mice, still had a defect in hepatobiliary cholesterol secretion, which was consistent with TKO versus NPC1L1(-/-) mice exhibiting a 52% reduction in fecal cholesterol excretion. Because fractional cholesterol absorption was reduced similarly in NPC1L1(-/-) and TKO mice, by subtracting fecal cholesterol excretion in TKO mice from NPC1L1(-/-) mice, we estimated that a 25g NPC1L1(-/-) mouse may secrete about 4 mumol of cholesterol daily via the G5/G8 pathway. In conclusion, NPC1L1 is essential for phytosterols to enter the body in mice.     

The Strength of Selection Against the Yeast Prion [PSI+]

The [PSI⁺] prion causes widespread readthrough translation and is rare in natural populations of Saccharomyces, despite the fact that sex is expected to cause it to spread. Using the recently estimated rate of Saccharomyces outcrossing, we calculate the strength of selection necessary to maintain [PSI⁺] at levels low enough to be compatible with data. Using the best available parameter estimates, we find selection against [PSI⁺] to be significant. Inference regarding selection on modifiers of [PSI⁺] appearance depends on obtaining more precise and accurate estimates of the product of yeast effective population size N_e and the spontaneous rate of [PSI⁺] appearance m. The ability to form [PSI⁺] has persisted in yeast over a long period of evolutionary time, despite a diversity of modifiers that could abolish it. If mN_e < 1, this may be explained by insufficiently strong selection. If mN_e > 1, then selection should favor the spread of [PSI⁺] resistance modifiers. In this case, rare conditions where [PSI⁺] is adaptive may permit its persistence in the face of negative selection.     

Regulation of the xylan-degrading apparatus of Cellvibrio japonicus by a novel two-component system

The microbial degradation of lignocellulose biomass is not only an important biological process but is of increasing industrial significance in the bioenergy sector. The mechanism by which the plant cell wall, an insoluble composite structure, activates the extensive repertoire of microbial hydrolytic enzymes required to catalyze its degradation is poorly understood. Here we have used a transposon mutagenesis strategy to identify a genetic locus, consisting of two genes that modulate the expression of xylan side chain-degrading enzymes in the saprophytic bacterium Cellvibrio japonicus. Significantly, the locus encodes a two-component signaling system, designated AbfS (sensor histidine kinase) and AbfR (response regulator). The AbfR/S two-component system is required to activate the expression of the suite of enzymes that remove the numerous side chains from xylan, but not the xylanases that hydrolyze the beta1,4-linked xylose polymeric backbone of this polysaccharide. Studies on the recombinant sensor domain of AbfS (AbfS(SD)) showed that it bound to decorated xylans and arabinoxylo-oligosaccharides, but not to undecorated xylo-oligosaccharides or other plant structural polysaccharides/oligosaccharides. The crystal structure of AbfS(SD) was determined to a resolution of 2.6A(.) The overall fold of AbfS(SD) is that of a classical Per Arndt Sim domain with a central antiparallel four-stranded beta-sheet flanked by alpha-helices. Our data expand the number of molecules known to bind to the sensor domain of two-component histidine kinases to include complex carbohydrates. The biological rationale for a regulatory system that induces enzymes that remove the side chains of xylan, but not the hydrolases that cleave the backbone of the polysaccharide, is discussed.     

Fertilizer affects the behaviour and performance of Plutella xylostella on brassicas

1 Foliar nitrogen concentration, which can be manipulated in crop plants by fertilizer supply, has long been recognized as a major factor in phytophagous insect abundance and performance. More recently, the type of fertilizer supplied has been shown to influence the abundance of some herbivore species. The diamondback moth Plutella xylostella is a global pest of Brassica crops. Although it has been the subject of numerous studies on host-plant resistance and pest control, few studies have addressed the effect of abiotic factors, such as nutrient supply, on its performance and behaviour.
2 We assessed oviposition preference, larval feeding preference and larval performance of P. xylostella on two cultivars of Brassica oleracea . Plants were grown using two fertilizer types, John Innes fertilizer and an organic animal manure, at high and low concentrations.
3  Plutella xylostella laid more eggs on cultivar Derby Day than Drago. Derby Day was also the cultivar on which larval performance was maximized. However, differences in larval performance between cultivars were only found when plants were grown in compost with John Innes fertilizer, and not when fertilized with animal manure.
4 Foliar nitrogen concentration was greater in plants grown in high fertilizer treatments but did not differ between cultivars. The concentrations of three glucosinolate compounds (glucoiberin, sinigrin and glucobrassicin) were greater in the high fertilizer treatments. Glucosinolate concentrations were higher in the Drago than the Derby Day cultivar.
5 These results are discussed in relation to the preference-performance hypothesis, and the assessment of plant resistance differences between cultivars using different types of fertilizer.     

Analysis of a post-translational steroid induction system for GIGANTEA in Arabidopsis

Background  

To investigate the link between the flowering time gene GIGANTEA (GI) and downstream genes, an inducible GI system was developed in Arabidopsis thaliana L. Heynh. Transgenic Arabidopsis plant lines were generated with a steroid-inducible post-translational control system for GI. The gene expression construct consisted of the coding region of the GI protein fused to that of the ligand binding domain of the rat glucocorticoid receptor (GR). This fusion gene was expressed from the constitutive cauliflower mosaic virus 35S promoter and was introduced into plants carrying the gi-2 mutation. Application of the steroid dexamethasone (DEX) was expected to result in activation of the GI-GR protein and its relocation from the cytoplasm to the nucleus.     

The low abundance of clonally expanded mitochondrial DNA point mutations in aged substantia nigra neurons

Clonally expanded mitochondrial DNA (mtDNA) deletions accumulate with age in human substantia nigra (SN) and high levels cause respiratory chain deficiency. In other human tissues, mtDNA point mutations clonally expand with age. Here, the abundance of mtDNA point mutations within single SN neurons from aged controls was investigated. From 31 single cytochrome c oxidase normal SN neurons, only one clonally expanded mtDNA point mutation was identified, suggesting in these neurons mtDNA point mutations occur rarely, whereas mtDNA deletions are frequently observed. This contrasts observations in mitotic tissues and suggests that different forms of mtDNA maintenance may exist in these two cell types.