Voltage-gated sodium channels from the bees Apis mellifera and Bombus terrestris are differentially modulated by pyrethroid insecticides.

Recent experimental and in-field evidence of the deleterious effects of insecticides on the domestic honey bee Apis mellifera have led to a tightening of the risk assessment requirements of these products, and now more attention is being paid to their sublethal effects on other bee species. In addition to traditional tests, in vitro and in silico approaches may become essential tools for a comprehensive understanding of the impact of insecticides on bee species. Here we present a study in which electrophysiology and a Markovian multi-state modelling of the voltage-gated sodium channel were used to measure the susceptibility of the antennal lobe neurons from Apis mellifera and Bombus terrestris, to the pyrethroids tetramethrin and esfenvalerate. Voltage-gated sodium channels from Apis mellifera and Bombus terrestris are differentially sensitive to pyrethroids. In both bee species, the level of neuronal activity played an important role in their relative sensitivity to pyrethroids. This work supports the notion that honey bees cannot unequivocally be considered as a surrogate for other bee species in assessing their neuronal susceptibility to insecticides.

Nerve injury induces a Gem-GTPase-dependent downregulation of P/Q-type Ca2+ channels contributing to neurite plasticity in dorsal root ganglion neurons.

Small RGK GTPases, Rad, Gem, Rem1, and Rem2, are potent inhibitors of high-voltage-activated (HVA) Ca(2+) channels expressed in heterologous expression systems. However, the role of this regulation has never been clearly demonstrated in the nervous system. Using transcriptional analysis, we show that peripheral nerve injury specifically upregulates Gem in mice dorsal root ganglia. Following nerve injury, protein expression was increased in ganglia and peripheral nerve, mostly under its phosphorylated form. This was confirmed in situ and in vitro in dorsal root ganglia sensory neurons. Knockdown of endogenous Gem, using specific small-interfering RNA (siRNA), increased the HVA Ca(2+) current only in the large-somatic-sized neurons. Combining pharmacological analysis of the HVA Ca(2+) currents together with Gem siRNA-transfection of larger sensory neurons, we demonstrate that only the P/Q-type Ca(2+) channels were enhanced. In vitro analysis of Gem affinity to various CaVßx-CaV2.x complexes and immunocytochemical studies of Gem and CaVß expression in sensory neurons suggest that the specific inhibition of the P/Q channels relies on both the regionalized upregulation of Gem and the higher sensitivity of the endogenous CaV2.1-CaVß4 pair in a subset of sensory neurons including the proprioceptors. Finally, pharmacological inhibition of P/Q-type Ca(2+) current reduces neurite branching of regenerating axotomized neurons. Taken together, the present results indicate that a Gem-dependent P/Q-type Ca(2+) current inhibition may contribute to general homeostatic mechanisms following a peripheral nerve injury.

Negative regulation of transcription by the type II arginine methyltransferase PRMT5.

We have identified previously a repressor element in the transcription start site region of the cyclin E1 promoter that periodically associates with an atypical, high molecular weight E2F complex, termed CERC. Purification of native CERC reveals the presence of the type II arginine methyltransferase PRMT5, which can mono- or symetrically dimethylate arginine residues in proteins. Chromatin immunoprecipitations (ChIPs) show that PRMT5 is associated specifically with the transcription start site region of the cyclin E1 promoter. ChIP analyses also show that this correlates with the presence on the same promoter region of arginine-methylated proteins including histone H4, an in vitro substrate of PRMT5. Consistent with its presence within the repressor complex, forced expression of PRMT5 negatively affects cyclin E1 promoter activity and cellular proliferation, effects that require its methyltransferase activity. These data provide the first direct experimental evidence that a type II arginine methylase is involved in the control of transcription and proliferation.

Electrophysiological characterization of tomato hypocotyl putative action potentials induced by cotyledon heating.

Young tomato plants (Lycopersicon esculentum, 8 days old) were given a heat-wound to a cotyledon. The resulting electrical activity at the hypocotyl level was monitored with intracellular microelectrodes. We observed an original pattern of slow wave potentials (SWPs), consisting of 2-3 slow waves, with associated spikes. The electrophysiological study of the SWPs confirms previous conclusions that the SWPs are due to the inhibition of an active component of the membrane potential. The electrophysiological study of the spikes shows that they fit particularities of putative action potentials (APs). They seem to be triggered by the depolarization accompanying the SWPs and thus can appear late during the SWP. An ionic characterization of the spikes by using different extracellular ionic concentrations and channel blockers suggests that anionic channels might be involved, carrying SO42- ions. The channels activity might be down regulated by the calcium released by the vacuole during the SWPs and APs. A better characterization of the nature of these APs could permit the understanding of the information transmission mechanisms in higher plants.