The 2'-O-ribose methyltransferase for cap 1 of spliced leader RNA and U1 small nuclear RNA in Trypanosoma brucei

mRNA cap 1 2'-O-ribose methylation is a widespread modification that is implicated in processing, trafficking, and translational control in eukaryotic systems. The eukaryotic enzyme has yet to be identified. In kinetoplastid flagellates trans-splicing of spliced leader (SL) to polycistronic precursors conveys a hypermethylated cap 4, including a cap 0 m7G and seven additional methylations on the first 4 nucleotides, to all nuclear mRNAs. We report the first eukaryotic cap 1 2'-O-ribose methyltransferase, TbMTr1, a member of a conserved family of viral and eukaryotic enzymes. Recombinant TbMTr1 methylates the ribose of the first nucleotide of an m7G-capped substrate. Knockdowns and null mutants of TbMTr1 in Trypanosoma brucei grow normally, with loss of 2'-O-ribose methylation at cap 1 on substrate SL RNA and U1 small nuclear RNA. TbMTr1-null cells have an accumulation of cap 0 substrate without further methylation, while spliced mRNA is modified efficiently at position 4 in the absence of 2'-O-ribose methylation at position 1; downstream cap 4 methylations are independent of cap 1. Based on TbMTr1-green fluorescent protein localization, 2'-O-ribose methylation at position 1 occurs in the nucleus. Accumulation of 3'-extended SL RNA substrate indicates a delay in processing and suggests a synergistic role for cap 1 in maturation.     

Modelling the transition from simple to complex Ca2+oscillations in pancreatic acinar cells

A mathematical model is proposed which systematically investigates complex calcium oscillations in pancreatic acinar cells. This model is based on calcium-induced calcium release via inositol trisphosphate receptors (IPR) and ryanodine receptors (RyR) and includes calcium modulation of inositol (1,4,5) trisphosphate (IP₃) levels through feedback regulation of degradation and production. In our model, the apical and the basal regions are separated by a region containing mitochondria, which is capable of restricting Ca²⁺ responses to the apical region. We were able to reproduce the observed oscillatory patterns, from baseline spikes to sinusoidal oscillations. The model predicts that calcium-dependent production and degradation of IP₃ is a key mechanism for complex calcium oscillations in pancreatic acinar cells. A partial bifurcation analysis is performed which explores the dynamic behaviour of the model in both apical and basal regions.     

Alcohol is a potent stimulant of immature neuronal networks: implications for fetal alcohol spectrum disorder

Ethanol consumption during development affects the maturation of hippocampal circuits by mechanisms that are not fully understood. Ethanol acts as a depressant in the mature CNS and it has been assumed that this also applies to immature neurons. We investigated whether ethanol targets the neuronal network activity that is involved in the refinement of developing hippocampal synapses. This activity appears during the growth spurt period in the form of giant depolarizing potentials (GDPs). GDPs are generated by the excitatory actions of GABA and glutamate via a positive feedback circuit involving pyramidal neurons and interneurons. We found that ethanol potently increases GDP frequency in the CA3 hippocampal region of slices from neonatal rats. It also increased the frequency of GDP-driven Ca2+ transients in pyramidal neurons and increased the frequency of GABA(A) receptor-mediated spontaneous postsynaptic currents in CA3 pyramidal cells and interneurons. The ethanol-induced potentiation of GABAergic activity is probably the result of increased quantal GABA release at interneuronal synapses but not enhanced neuronal excitability. These findings demonstrate that ethanol is a potent stimulant of developing neuronal circuits, which might contribute to the abnormal hippocampal development associated with fetal alcohol syndrome and alcohol-related neurodevelopmental disorders.     

Phospholipin, a novel heterodimeric phospholipase A2 from Pandinus imperator scp6pion venom.

The primary structure of a phospholipase A2, with unique structural and functional characteristics, was determined. The large subunit has 108 amino acid residues, linked by a disulfide bridge to the small subunit, which contains 17 residues. Its gene was cloned from a cDNA library. The nucleotide sequence showed that the same RNA messenger encodes both subunits, separated only by a pentapeptide, that is processed during maturation.     

Immobility response elicited by clamping the neck induces antinociception in a "tonic pain" test in mice

Clamping the neck followed by body inversion to a supine position in mice elicits an immobility response called immobility by clamping the neck (ICN). The noxious pinch to the scruff of the neck produces antinociception in "phasic pain" models (e.g. tail-flick test). Here, a "tonic pain" model was used to test the antinociception associated with the ICN, and naloxone was used to determine the role of opioids in such antinociception. Mice were injected intraperitoneally with 0.3 mL of 0.4% acetic acid to produce writhing responses that were measured for one hour. ICN was induced every five minutes for one hour. Naloxone (5 mg/kg ip) was injected 10 min before acetic acid administration. There was a control group, sham clamping (SCLA). These mice were handled and restricted every five minutes as in the ICN but without real clamping. The repetitive inductions of ICN were able to reduce the writhing behavior; this antinociception was blocked by the naloxone pretreatment. In the SCLA group antinociception was not observed. These findings indicate that as in the "phasic pain" model, ICN also was able to elicit antinociception in this "tonic pain" model, and such antinociception seems to be mediated by opioids.