Influence of type of dietary fat on the prostaglandin release from isolated rabbit and rat hearts and from rat aortas

It has previously been found (1) that feeding rats a diet containing a high amount of sunflowerseed oil results in a higher coronary flow and left ventricular work of their isolated hearts as compared to hearts of rats fed hydrogenated coconut oil or lard. It was hypothesized that this phenomenon can be explained by an influence of dietary linoleic acid on prostaglandin synthesis in the heart. To verify this hypothesis rabbits and rats were fed for four weeks sunflowerseed oil (SSO), hydrogenated coconut oil (HCO) or lard (L) to a maximum of 30 to 40 per cent of the total digestable energy, and the prostaglandin release from the isolated perfused hearts and rat aortas was determined by gas chromatography and bio-assay (PGI₂).For the isolated hearts of rabbits fed SSO, the release of PGE₂, PGF_2α and 6-oxo-PGF_1α was 1.7, 0.7 and 3.0 ng min⁻¹ g⁻¹ dry weight respectively; when fed L, these values were 2.9, 1.1 and 5.6 ng min⁻¹ g⁻¹. For the isolated hearts of rats fed SSO, HCO or L, the total release of PGE₂, PGD₂, PGF_2α and thromboxane B₂ (TXB₂) was 5.9, 5.8 and 5.6 ng min⁻¹ g⁻¹ respectively; the release of 6-oxo-PGF_1α was 3.4, 5.7 and 6.4 ng min⁻¹ g⁻¹ respectively. Relatively, 26% PGE₂, 13% PGD₂, 8% PGF_2α, 6% TXB₂ and 47% 6-oxo-PGF_1α were released. For the isolated aortas of rats fed SSO or HCO, the release of PGI₂-like activity was 0.37 ± 0.05 and 0.49 ± 0.05 ng min⁻¹ cm⁻². The release of PGI₂-like activity from hearts of EFA-deficient rats was about 20% of that from control hearts.We conclude that, although feeding sunflowerseed oil, with respect to feeding hydrogenated coconut oil or lard, does increase coronary flow and left ventricular work, it does not increase the basal prostaglandin production in the isolated rat or rabbit heart; instead there is a tendency for a lower PGI₂ synthesis.     

Effects of Mojave toxin on rat skeletal muscle sarcoplasmic reticulum.

Effects of the lethal fraction (MD-9) from the venom of the Mojave rattlesnake, Crotalus scutulatus, on sarcoplasmic reticulum were investigated. The calcium sequestering activity of the vesicles was reduced by the lethal fraction and subsequent release of calcium was enhanced. These effects were observed to be dependent upon MD-9 concentration and the length of preincubation time with the vesicles. An enhanced ATPase activity that was affected by concentration and MD-9 preincubation time was also observed. Both calcium uptake and ATPase activity effects may be due to a phospholipase activity associated with the fraction.     

MAGI-1 Modulates AMPA Receptor Synaptic Localization and Behavioral Plasticity in Response to Prior Experience

It is well established that the efficacy of synaptic connections can be rapidly modified by neural activity, yet how the environment and prior experience modulate such synaptic and behavioral plasticity is only beginning to be understood. Here we show in C. elegans that the broadly conserved scaffolding molecule MAGI-1 is required for the plasticity observed in a glutamatergic circuit. This mechanosensory circuit mediates reversals in locomotion in response to touch stimulation, and the AMPA-type receptor (AMPAR) subunits GLR-1 and GLR-2, which are required for reversal behavior, are localized to ventral cord synapses in this circuit. We find that animals modulate GLR-1 and GLR-2 localization in response to prior mechanosensory stimulation; a specific isoform of MAGI-1 (MAGI-1L) is critical for this modulation. We show that MAGI-1L interacts with AMPARs through the intracellular domain of the GLR-2 subunit, which is required for the modulation of AMPAR synaptic localization by mechanical stimulation. In addition, mutations that prevent the ubiquitination of GLR-1 prevent the decrease in AMPAR localization observed in previously stimulated magi-1 mutants. Finally, we find that previously-stimulated animals later habituate to subsequent mechanostimulation more rapidly compared to animals initially reared without mechanical stimulation; MAGI-1L, GLR-1, and GLR-2 are required for this change in habituation kinetics. Our findings demonstrate that prior experience can cause long-term alterations in both behavioral plasticity and AMPAR localization at synapses in an intact animal, and indicate a new, direct role for MAGI/S-SCAM proteins in modulating AMPAR localization and function in the wake of variable sensory experience.     

Dominance and recessiveness at the protein level in mutant x wildtype crosses in Sacchaomyces cerevisiae

Summary The is ₁-locus of the yeast Saccharomyces cerevisiae is the structural gene for threonine dehydratase. is ₁-mutants require isoleucine for growth and do not have active threonine dehydratase.Interallelic complementation is frequent among is ₁-mutants. This is indicative for an aggregate or multimeric structure of yeast threonine dehydratase.Complementing and non-complementing mutants were crossed to wildtype. Properties of threonine dehydratase were assayed in crude extracts of the resulting heterozygotes.Specific activities varied considerably between full wildtype activity and a level about 10% of that. The apparent Michaelis constants were increased in many heterozygotes. This effect was probably due to the aggregation of both mutant and wildtype subunits to form a hybrid threonine dehydratase with reduced substrate affinity in addition to pure wildtype enzyme. This notion is supported by the observation in one heterozygote of two enzyme fractions with increased Michaelis constants in addition to a wildtype-like fraction.The possible formation of hybrid enzymes with normal, reduced or no activity is considered to blur gene dosage relations.A given pair of alleles in a heterozygous cell can generate a new type of enzyme with properties not encountered in the corresponding two homozygous cells. This situation is not accounted for by the classical concepts of dominant-recessive or intermediate behaviour, because the difference between the heterozygotes and the homozygotes is not necessarily only quantitativ but also qualitative.We dedicate this publication to Prof. Dr. C. Auerbach on occasion of her official retirement in admiration for her pioneer work and many contribution to genetics.     

The Internal Organization of Mycobacterial Partition Assembly: Does the DNA Wrap a Protein Core?

Before cell division in many bacteria, the ParBs spread on a large segment of DNA encompassing the origin-proximal parS site(s) to form the partition assembly that participates in chromosome segregation. Little is known about the structural organization of chromosomal partition assembly. We report solution X-ray and neutron scattering data characterizing the size parameters and internal organization of a nucleoprotein assembly formed by the mycobacterial chromosomal ParB and a 120-meric DNA containing a parS-encompassing region from the mycobacterial genome. The cross-sectional radii of gyration and linear mass density describing the rod-like ParB-DNA assembly were determined from solution scattering. A “DNA outside, protein inside” mode of partition assembly organization consistent with the neutron scattering hydrogen/deuterium contrast variation data is discussed. In this organization, the high scattering DNA is positioned towards the outer region of the partition assembly. The new results presented here provide a basis for understanding how ParBs organize the parS-proximal chromosome, thus setting the stage for further interactions with the DNA condensins, the origin tethering factors and the ParA.     

Disruption of Intrinsic Motions as a Mechanism for Enzyme Inhibition

Clostridium difficile (C. diff) is one of the most common and most severe hospital-acquired infections; its consequences range from lengthened hospital stay to outright lethality. C. diff causes cellular damage through the action of two large toxins TcdA and TcdB. Recently, there has been increased effort toward developing antitoxin therapies, rather than antibacterial treatments, in hopes of mitigating the acquisition of drug resistance. To date, no analysis of the recognition mechanism of TcdA or TcdB has been attempted. Here, we use small molecule flexible docking followed by unbiased molecular dynamics to obtain a more detailed perspective on how inhibitory peptides, exemplified by two species HQSPWHH and EGWHAHT function. Using principal component analysis and generalized masked Delaunay analysis, an examination of the conformational space of TcdB in its apo form as well as forms bound to the peptides and UDP-Glucose was performed. Although both species inhibit by binding in the active site, they do so in two very different ways. The simulations show that the conformational space occupied by TcdB bound to the two peptides are quite different and provide valuable insight for the future design of toxin inhibitors and other enzymes that interact with their substrates through conformational capture mechanisms and thus work by the disruption of the protein’s intrinsic motions.     

Genome‐wide association study of word reading: Overlap with risk genes for neurodevelopmental disorders

Reading disabilities (RD) are the most common neurocognitive disorder, affecting 5% to 17% of children in North America. These children often have comorbid neurodevelopmental/psychiatric disorders, such as attention deficit/hyperactivity disorder (ADHD). The genetics of RD and their overlap with other disorders is incompletely understood. To contribute to this, we performed a genome‐wide association study (GWAS) for word reading. Then, using summary statistics from neurodevelopmental/psychiatric disorders, we computed polygenic risk scores (PRS) and used them to predict reading ability in our samples. This enabled us to test the shared aetiology between RD and other disorders. The GWAS consisted of 5.3 million single nucleotide polymorphisms (SNPs) and two samples; a family‐based sample recruited for reading difficulties in Toronto (n = 624) and a population‐based sample recruited in Philadelphia [Philadelphia Neurodevelopmental Cohort (PNC)] (n = 4430). The Toronto sample SNP‐based analysis identified suggestive SNPs (P ~ 5 × 10^?7) in the ARHGAP23 gene, which is implicated in neuronal migration/axon pathfinding. The PNC gene‐based analysis identified significant associations (P < 2.72 × 10^?6) for LINC00935 and CCNT1, located in the region of the KANSL2/CCNT1/LINC00935/SNORA2B/SNORA34/MIR4701/ADCY6 genes on chromosome 12q, with near significant SNP‐based analysis. PRS identified significant overlap between word reading and intelligence (R² = 0.18, P = 7.25 × 10^?181), word reading and educational attainment (R² = 0.07, P = 4.91 × 10^?48) and word reading and ADHD (R² = 0.02, P = 8.70 × 10^?6; threshold for significance = 7.14 × 10^?3). Overlap was also found between RD and autism spectrum disorder (ASD) as top‐ranked genes were previously implicated in autism by rare and copy number variant analyses. These findings support shared risk between word reading, cognitive measures, educational outcomes and neurodevelopmental disorders, including ASD.