Brain-derived neurotrophic factor in the hypothalamic paraventricular nucleus reduces energy intake

Recent studies show that brain-derived neurotrophic factor (BDNF) decreases feeding and body weight after peripheral and ventricular administration. BDNF mRNA and protein, and its receptor tyrosine kinase B (TrkB) are widely distributed in the hypothalamus and other brain regions. However, there are few reports on specific brain sites of actions for BDNF. We evaluated the effect of BDNF in the hypothalamic paraventricular nucleus (PVN) on feeding. BDNF injected unilaterally or bilaterally into the PVN of food-deprived and nondeprived rats significantly decreased feeding and body weight gain within the 0- to 24-h and 24- to 48-h postinjection intervals. Effective doses producing inhibition of feeding behavior did not establish a conditioned taste aversion. PVN BDNF significantly decreased PVN neuropeptide Y (NPY)-induced feeding at 1, 2, and 4 h following injection. BDNF administration in the PVN abolished food-restriction-induced NPY gene expression in the hypothalamic arcuate nucleus. In conclusion, BDNF in the PVN significantly decreases food intake and body weight gain, suggesting that the PVN is an important site of action for BDNF in its effects on energy metabolism. Furthermore, BDNF appears to interact with NPY in its anorectic actions, although a direct effect on NPY remains to be established.     

Fatty Acid Competition as a Mechanism by Which Enterobacter cloacae Suppresses Pythium ultimum Sporangium Germination and Damping-Off

Interactions between plant-associated microorganisms play important roles in suppressing plant diseases and enhancing plant growth and development. While competition between plant-associated bacteria and plant pathogens has long been thought to be an important means of suppressing plant diseases microbiologically, unequivocal evidence supporting such a mechanism has been lacking. We present evidence here that competition for plant-derived unsaturated long-chain fatty acids between the biological control bacterium Enterobacter cloacae and the seed-rotting oomycete, Pythium ultimum, results in disease suppression. Since fatty acids from seeds and roots are required to elicit germination responses of P. ultimum, we generated mutants of E. cloacae to evaluate the role of E. cloacae fatty acid metabolism on the suppression of Pythium sporangium germination and subsequent plant infection. Two mutants of E. cloacae EcCT-501R3, Ec31 (fadB) and EcL1 (fadL), were reduced in β-oxidation and fatty acid uptake, respectively. Both strains failed to metabolize linoleic acid, to inactivate the germination-stimulating activity of cottonseed exudate and linoleic acid, and to suppress Pythium seed rot in cotton seedling bioassays. Subclones containing fadBA or fadL complemented each of these phenotypes in Ec31 and EcL1, respectively. These data provide strong evidence for a competitive exclusion mechanism for the biological control of P. ultimum-incited seed infections by E. cloacae where E. cloacae prevents the germination of P. ultimum sporangia by the efficient metabolism of fatty acid components of seed exudate and thus prevents seed infections.     

Unexpected Relationships and Inbreeding in HapMap Phase III Populations

Correct annotation of the genetic relationships between samples is essential for population genomic studies, which could be biased by errors or omissions. To this end, we used identity-by-state (IBS) and identity-by-descent (IBD) methods to assess genetic relatedness of individuals within HapMap phase III data. We analyzed data from 1,397 individuals across 11 ethnic populations. Our results support previous studies (Pemberton et al., 2010; Kyriazopoulou-Panagiotopoulou et al., 2011) assessing unknown relatedness present within this population. Additionally, we present evidence for 1,657 novel pairwise relationships across 9 populations. Surprisingly, significant Cotterman''s coefficients of relatedness K1 (IBD1) values were detected between pairs of known parents. Furthermore, significant K2 (IBD2) values were detected in 32 previously annotated parent-child relationships. Consistent with a hypothesis of inbreeding, regions of homozygosity (ROH) were identified in the offspring of related parents, of which a subset overlapped those reported in previous studies (Gibson et al. 2010; Johnson et al. 2011). In total, we inferred 28 inbred individuals with ROH that overlapped areas of relatedness between the parents and/or IBD2 sharing at a different genomic locus between a child and a parent. Finally, 8 previously annotated parent-child relationships had unexpected K0 (IBD0) values (resulting from a chromosomal abnormality or genotype error), and 10 previously annotated second-degree relationships along with 38 other novel pairwise relationships had unexpected IBD2 (indicating two separate paths of recent ancestry). These newly described types of relatedness may impact the outcome of previous studies and should inform the design of future studies relying on the HapMap Phase III resource.     

Evaluation of endothelin-1-induced pulmonary vasoconstriction following myocardial infarction

Endothelin (ET) levels are elevated in congestive heart failure secondary to myocardial infarction (MI) and correlate well with the severity of pulmonary hypertension (PH), suggesting that the ET peptide could contribute to the pathophysiology of venous PH. Alterations of pulmonary vasoreactivity to ET after MI and the respective roles of the ET(A) and ET(B) receptors (ET(A)-R and ET(B)-R) have never been evaluated, to our knowledge. MI was induced in rats. Three weeks later, small pulmonary resistance arteries were mounted on a microvascular myograph. Cumulative concentration-response curves to ET-1 and sarafotoxin 6c (S6c) were performed. Response to ET was also assessed in the presence of ET-R antagonists. Heterodimerization of receptors was evaluated by immunoprecipitation of the ET(B)-R, followed by western blotting for the expression of the ET(A)-R. Maximal vasoconstriction and sensitivity to ET-1 were similar in sham and MI with values of 88 +/- 3.9% and 80 +/- 3.8%, respectively. The response to S6c was similarly less in both sham (67 +/- 5.7%) and MI groups (60 +/- 6.6%). When administered alone, the ET(A)-R antagonist (10 nM A-147627.1) and the ET(B)-R antagonist (1 microM A-192621.1) had no significant effect. However, their combination markedly reduced vaso-constriction (52 +/- 5.3%; P < 0.001). The endothelial and medial distribution of ET-Rs was similar in sham and MI groups. In vitro studies demonstrated co-immunoprecipitation of the ET(A)-R and ET(B)-R. Vasoconstriction of isolated resistance pulmonary arteries to ET agonists is not altered after MI. Dual antagonism results in optimal blockade of vasoconstriction, possibly because the ET(A)-R and ET(B)-R can form functional heterodimers.     

The crystal structure of the bifunctional primase-helicase of bacteriophage T7

Within minutes after infecting Escherichia coli, bacteriophage T7 synthesizes many copies of its genomic DNA. The lynchpin of the T7 replication system is a bifunctional primase-helicase that unwinds duplex DNA at the replication fork while initiating the synthesis of Okazaki fragments on the lagging strand. We have determined a 3.45 A crystal structure of the T7 primase-helicase that shows an articulated arrangement of the primase and helicase sites. The crystallized primase-helicase is a heptamer with a crown-like shape, reflecting an intimate packing of helicase domains into a ring that is topped with loosely arrayed primase domains. This heptameric isoform can accommodate double-stranded DNA in its central channel, which nicely explains its recently described DNA remodeling activity. The double-jointed structure of the primase-helicase permits a free range of motion for the primase and helicase domains that suggests how the continuous unwinding of DNA at the replication fork can be periodically coupled to Okazaki fragment synthesis.     

Identification of mitogen-activated protein/extracellular signal-responsive kinase kinase 2 as a novel partner of the scaffolding protein human homolog of disc-large

Human disc-large homolog (hDlg), also known as synapse-associated protein 97, is a scaffold protein, a member of the membrane-associated guanylate kinase family, implicated in neuronal synapses and epithelial-epithelial cell junctions whose expression and function remains poorly characterized in most tissues, particularly in the vasculature. In human vascular tissues, hDlg is highly expressed in smooth muscle cells (VSMCs). Using the yeast two-hybrid system to screen a human aorta cDNA library, we identified mitogen-activated protein/extracellular signal-responsive kinase (ERK) kinase (MEK)2, a member of the ERK cascade, as an hDlg binding partner. Site-directed mutagenesis showed a major involvement of the PSD-95, disc-large, ZO-1 domain-2 of hDlg and the C-terminal sequence RTAV of MEK2 in this interaction. Coimmunoprecipitation assays in both human VSMCs and human embryonic kidney 293 cells, demonstrated that endogenous hDlg physically interacts with MEK2 but not with MEK1. Confocal microscopy suggested a colocalization of the two proteins at the inner layer of the plasma membrane of confluent human embryonic kidney 293 cells, and in a perinuclear area in human VSMCs. Additionally, hDlg also associates with the endoplasmic reticulum and microtubules in these latter cells. Taken together, these findings allow us to hypothesize that hDlg acts as a MEK2-specific scaffold protein for the ERK signaling pathway, and may improve our understanding of how scaffold proteins, such as hDlg, differentially tune MEK1/MEK2 signaling and cell responses.