Senescent leaf exudate increases mosquito survival and microbial activity

We conducted experiments to evaluate the effects of soluble components in senescent leaf material on the growth and development of the eastern tree hole mosquito, Aedes triseriatus (Say). Oak leaves that were either leached for three days to remove the labile nutrient fraction, or were not leached, served as basal nutrient inputs in each experiment.Mosquito performance in microcosms containing leachate only was significantly worse compared with microcosms containing leaf material in combination with either leachate or water, indicating the importance of leaf substrates to mosquito production.Adult mosquito biomass, emergence, and development time were significantly higher in microcosms containing unleached leaves compared with leached leaf material. Additions of leachate to leached leaf treatments enhanced adult production, but not to the level observed in unleached leaf treatments.Filtered and unfiltered leachate added substantial nitrogen and phosphorus to microcosms and significantly affected mosquito growth responses. Bacterial productivity and abundance were also significantly affected by leachate additions and filtering.Taken together, these results suggest that while leaves decline with respect to nutritional value during decomposition, they remain important components of the habitat as substrates for microbial growth and mosquito feeding, particularly when nutrients (here, leachate) enter the system. Our results also illustrate the importance of soluble leaf material, which enhances mosquito production through effects on microbial community dynamics.     

Triglycerides in the Human Kidney Cortex: Relationship with Body Size

Obesity is associated with increased risk for kidney disease and uric acid nephrolithiasis, but the pathophysiological mechanisms underpinning these associations are incompletely understood. Animal experiments have suggested that renal lipid accumulation and lipotoxicity may play a role, but whether lipid accumulation occurs in humans with increasing body mass index (BMI) is unknown. The association between obesity and abnormal triglyceride accumulation in non-adipose tissues (steatosis) has been described in the liver, heart, skeletal muscle and pancreas, but not in the human kidney. We used a quantitative biochemical assay to quantify triglyceride in normal kidney cortex samples from 54 patients undergoing nephrectomy for localized renal cell carcinoma. In subsets of the study population we evaluated the localization of lipid droplets by Oil Red O staining and measured 16 common ceramide species by mass spectrometry. There was a positive correlation between kidney cortex trigyceride content and BMI (Spearman R = 0.27, P = 0.04). Lipid droplets detectable by optical microscopy had a sporadic distribution but were generally more prevalent in individuals with higher BMI, with predominant localization in proximal tubule cells and to a lesser extent in glomeruli. Total ceramide content was inversely correlated with triglycerides. We postulate that obesity is associated with abnormal triglyceride accumulation (steatosis) in the human kidney. In turn, steatosis and lipotoxicity may contribute to the pathogenesis of obesity-associated kidney disease and nephrolithiasis.     

The Eps1p Protein Disulfide Isomerase Conserves Classic Thioredoxin Superfamily Amino Acid Motifs but Not Their Functional Geometries

The widespread thioredoxin superfamily enzymes typically share the following features: a characteristic α-β fold, the presence of a Cys-X-X-Cys (or Cys-X-X-Ser) redox-active motif, and a proline in the cis configuration abutting the redox-active site in the tertiary structure. The Cys-X-X-Cys motif is at the solvent-exposed amino terminus of an α-helix, allowing the first cysteine to engage in nucleophilic attack on substrates, or substrates to attack the Cys-X-X-Cys disulfide, depending on whether the enzyme functions to reduce, isomerize, or oxidize its targets. We report here the X-ray crystal structure of an enzyme that breaks many of our assumptions regarding the sequence-structure relationship of thioredoxin superfamily proteins. The yeast Protein Disulfide Isomerase family member Eps1p has Cys-X-X-Cys motifs and proline residues at the appropriate primary structural positions in its first two predicted thioredoxin-fold domains. However, crystal structures show that the Cys-X-X-Cys of the second domain is buried and that the adjacent proline is in the trans, rather than the cis isomer. In these configurations, neither the “active-site” disulfide nor the backbone carbonyl preceding the proline is available to interact with substrate. The Eps1p structures thus expand the documented diversity of the PDI oxidoreductase family and demonstrate that conserved sequence motifs in common folds do not guarantee structural or functional conservation.     

The Effect of Inversion at 8p23 on BLK Association with Lupus in Caucasian Population

To explore the potential influence of the polymorphic 8p23.1 inversion on known autoimmune susceptibility risk at or near BLK locus, we validated a new bioinformatics method that utilizes SNP data to enable accurate, high-throughput genotyping of the 8p23.1 inversion in a Caucasian population. Methods: Principal components analysis (PCA) was performed using markers inside the inversion territory followed by k-means cluster analyses on 7416 European derived and 267 HapMaP CEU and TSI samples. A logistic regression conditional analysis was performed. Results: Three subgroups have been identified; inversion homozygous, heterozygous and non-inversion homozygous. The status of inversion was further validated using HapMap samples that had previously undergone Fluorescence in situ hybridization (FISH) assays with a concordance rate of above 98%. Conditional analyses based on the status of inversion were performed. We found that overall association signals in the BLK region remain significant after controlling for inversion status. The proportion of lupus cases and controls (cases/controls) in each subgroup was determined to be 0.97 for the inverted homozygous group (1067 cases and 1095 controls), 1.12 for the inverted heterozygous group (1935 cases 1717 controls) and 1.36 for non-inverted subgroups (924 cases and 678 controls). After calculating the linkage disequilibrium between inversion status and lupus risk haplotype we found that the lupus risk haplotype tends to reside on non-inversion background. As a result, a new association effect between non-inversion status and lupus phenotype has been identified ((p = 8.18×10⁻⁷, OR = 1.18, 95%CI = 1.10–1.26). Conclusion: Our results demonstrate that both known lupus risk haplotype and inversion status act additively in the pathogenesis of lupus. Since inversion regulates expression of many genes in its territory, altered expression of other genes might also be involved in the development of lupus.     

Central metabolic fluxes in the endosperm of developing maize seeds and their implications for metabolic engineering

1?C labeling experiments performed with kernel cultures showed that developing maize endosperm is more efficient than other non-photosynthetic tissues such as sunflower and maize embryos at converting maternally supplied substrates into biomass. To characterize the metabolic fluxes in endosperm, maize kernels were labeled to isotopic steady state using 13C-labeled glucose. The resultant labeling in free metabolites and biomass was analyzed by NMR and GC-MS. After taking into account the labeling of substrates supplied by the metabolically active cob, the fluxes through central metabolism were quantified by computer-aided modeling. The flux map indicates that 51-69% of the ATP produced is used for biomass synthesis and up to 47% is expended in substrate cycling. These findings point to potential engineering targets for improving yield and increasing oil contents by, respectively, reducing substrate cycling and increasing the commitment of plastidic carbon into fatty acid synthesis at the level of pyruvate kinase.     

B-RAF: A contributor to the melanoma phenotype

B-RAF, a serine-threonine protein kinase, is one of the three RAF paralogs in humans. B-RAF participates in the RAS-RAF-MEK-ERK pathway, a conserved protein kinase-signalling cascade that is involved in regulating a number of critical cellular functions. Mutated B-RAF is believed to play a crucial role in the development, maintenance and progression of melanoma, where it contributes to multiple aspects of the malignant phenotype, such as cell survival, proliferation and apoptosis resistance. Indeed, it is mutated in a high proportion of melanocytic skin lesions and B-RAF mutations are preserved through melanoma progression. Despite this, the direct inhibition of B-RAF has shown little success clinically in the treatment of melanoma, presumably due to the complexity of the RAS-RAF-MEK-ERK pathway. For this reason, alternative strategies must be developed to treat oncogenic B-RAF-induced melanomas.     

iRhoms: ERADicating the messenger in growth control signaling

iRhoms are inactive rhomboid-like pseudoproteases that lack essential catalytic residues. Although iRhoms are highly conserved in metazoan species, little is known about their function. In a recent issue of Cell, Zettl et?al. (2011) show that iRhoms regulate growth factor signaling through endoplasmic reticulum-associated protein degradation (ERAD).