Go α is involved in sugar perception in Drosophila

Detection of chemical compounds in food sources is based on the activation of 7 transmembrane gustatory receptors (GRs) in mammals and in insects such as Drosophila, although the receptors are not conserved between the classes. Different combinations of Drosophila GRs are involved in the detection of sugars, but the activated signaling cascades are largely unknown. Because 7 transmembrane receptors usually couple to G-proteins, we tried to unravel the intracellular signaling cascade in taste neurons by screening heterotrimeric G-protein mutant flies for gustatory deficits. We found the subunit Goα to be involved in feeding behavior and cell excitability by different transgenic and pharmacological approaches. Goα is involved in the detection of sucrose, glucose, and fructose, but not with trehalose and maltose. Our studies reveal that Goα plays an important role in the perception of some sweet tastants. Because the perception of other sweet stimuli was not affected by mutations in Goα, we also found strong indication for the existence of multiple signaling pathways in the insect gustatory system.     

Deep soil carbon dynamics are driven more by soil type than by climate: a worldwide meta‐analysis of radiocarbon profiles

The response of soil carbon dynamics to climate and land‐use change will affect both the future climate and the quality of ecosystems. Deep soil carbon (>20 cm) is the primary component of the soil carbon pool, but the dynamics of deep soil carbon remain poorly understood. Therefore, radiocarbon activity (C), which is a function of the age of carbon, may help to understand the rates of soil carbon biodegradation and stabilization. We analyzed the published C contents in 122 profiles of mineral soil that were well distributed in most of the large world biomes, except for the boreal zone. With a multivariate extension of a linear mixed‐effects model whose inference was based on the parallel combination of two algorithms, the expectation–maximization (EM) and the Metropolis–Hasting algorithms, we expressed soil C profiles as a four‐parameter function of depth. The four‐parameter model produced insightful predictions of soil C as dependent on depth, soil type, climate, vegetation, land‐use and date of sampling (). Further analysis with the model showed that the age of topsoil carbon was primarily affected by climate and cultivation. By contrast, the age of deep soil carbon was affected more by soil taxa than by climate and thus illustrated the strong dependence of soil carbon dynamics on other pedologic traits such as clay content and mineralogy.     

Timberol? Inhibits TAAR5-Mediated Responses to Trimethylamine and Influences the Olfactory Threshold in Humans

In mice, trace amine-associated receptors (TAARs) are interspersed in the olfactory epithelium and constitute a chemosensory subsystem that is highly specific for detecting volatile amines. Humans possess six putative functional TAAR genes. Human TAAR5 (hTAAR5) is highly expressed in the olfactory mucosa and was shown to be specifically activated by trimethylamine. In this study, we were challenged to uncover an effective blocker substance for trimethylamine-induced hTAAR5 activation. To monitor blocking effects, we recombinantly expressed hTAAR5 and employed a commonly used Cre-luciferase reporter gene assay. Among all tested potential blocker substances, Timberol®, an amber-woody fragrance, is able to inhibit the trimethylamine-induced hTAAR5 activation up to 96%. Moreover, human psychophysical data showed that the presence of Timberol® increases the olfactory detection threshold for the characteristic fishy odor of trimethylamine by almost one order of magnitude. In conclusion, our results show that among tested receptors Timberol® is a specific and potent antagonist for the hTAAR5-mediated response to trimethylamine in a heterologous system. Furthermore, our data concerning the observed shift of the olfactory detection threshold in vivo implicate that hTAAR5 or other receptors that may be inhibited by Timberol® could be involved in the high affinity olfactory perception of trimethylamine in humans.     

Structural requirements of amino acids and related compounds for stimulation of receptors in crayfish walking leg

Summary Previous recordings from single afferent neurons in the walking legs of the crayfish demonstrated the presence of amino acid sensitivity; several characteristics of this extracellularly recorded impulse discharge, such as responses to mixtures of effective amino acids and cross adaptation experiments, indicate that all such units represent a single type of receptor. Here the effectiveness of more than 100 systematically varying amino acids and analog substances were tested in eliciting a response of the cell. Molecules lacking the amino or carboxyl group were found to be ineffective. The amino group must be unsubstituted and bear an ionic charge; modifications of the carboxyl group, including removal of charge, are tolerated with some loss of effectiveness. Replacement of the-hydrogen by a methyl group reduced effectiveness by about 1 decade. Amino acids not in the L configuration, or the amino group of which was not in the position, were still less effective. The affinity of the amino acids for the receptor was related to the number of C atoms in the side chain, with a maximum at 3. Molecules with voluminous, hydrophobic or negatively charged side chains had little effect. For high effectiveness, the side chain should be short and bear a hydrophilic group, but there is relatively little restriction on its chemical properties. These findings suggest the presence of three subunits in the receptive area. One of the proposed subunits would be involved in ionic binding to the amino group and the two others, in the formation of hydrogen bridges to the carboxyl group and the side chain. Their orientation with respect to one another would be expected to meet certain steric requirements.     

Patch-clamp recordings of spiking and nonspiking interneurons from rabbit olfactory bulb slices: GABA- and other transmitter receptors

Summary Transmitter receptor ion channels from previously identified rabbit olfactory bulb neurons were studied by using a thin slice preparation in combination with patch-clamp measurements. PG cells, which closely resembled previously described periglomerular interneurons in their morphology, responded to microapplication of GABA, acetylcholine, norepinephrine and glycine with the activation of distinct ionic currents. JG cells, which belong either to the class of short axon cells or external tufted cells, never showed GABA responses. In mitral cells ionic currents activated by GABA, acetylcholine, norepinephrine and glutamate could be elicited. Further measurements of GABA-activated currents of PG cells were made and indicated that these cells expressed two different types of GABA receptors: one which showed fast desensitization with a decay time constant of about 5 s, and one which slowly desensitized with a decay time constant of about 20–30 s. Both types were completely inhibited by bicuculline methiodide (50 M). GABA receptors were not blocked by Zn²⁺ (0.1 mM). From the dose-response relationship of the peak GABA-activated currents, an apparent dissociation constant of 50 M was derived. From single channel measurements in excised outside-out patches, a single channel conductance of GABA-activated Cl^– currents of 24 pS was obtained during continuous application of the agonist. Single channel events had a mean open time of 1.9 ms.     

Combining E-β-farnesene and methyl salicylate release with wheat-pea intercropping enhances biological control of aphids in North China

Combining intercropping with the release of semiochemicals may strengthen biological control of aphids as a push-pull strategy that simultaneously repels aphids and attracts their natural enemies. This hypothesis was tested in the Henan Province of China in 2016 where aphids, their natural enemies and mummies were trapped and observed on crops in three treatments: wheat-pea strip intercropping solely (control), intercropping combined with the release of E-β-farnesene (EBF) and intercropping combined with the release of methyl salicylate (MeSA). Each treatment was repeated four times. The abundance of aphids throughout the growing season (9 weeks between March and May) was significantly decreased and the abundance of natural enemies and mummies were significantly increased in treatments with releases of semiochemicals compared to intercropping solely. The effect was stronger with MeSA than with EBF on the control of Rhopalosiphum padi and pea aphids as well as on the attraction of lacewings and hoverflies. Indeed, lacewings and hoverflies were on average twice more numerous in MeSA than in the other treatments. These results show that combining wheat-pea intercropping with the release of EBF or MeSA can significantly reduce aphid density and attract their natural enemies and that this effect is strengthen with MeSA when compared to EBF.     

A family of glutamatergic,excitatory channel types at the crayfish neuromuscular junction

Summary Outside-out patches from membrane of muscles of crayfish (Austropotamobius torrentium) were excised, and L-glutamate (glu) was applied to these patches in pulses of different duration, performing a concentration step within about 0.2 ms. While a uniform population of cationic channels is seen in equilibrium applications of glu, four kinetically different channel types were revealed by the pulse applications of glu. All these channel types had the same single channel conductance and durations of elementary short single channel openings and closings, and they thus form a family of channels. Type I, incompletely desensitizing channels reacted to a pulse of 10 mM glu with a peak open probability of 0.7 within 0.3 ms. Thereafter open probability decayed with a time constant of desensitization of about 5 ms, reaching a plateau of about 1/20 peak probability which was maintained as long as 10 mM glu were present. The peak probabilities of channel opening were proportional to approximately power 2.5 of the glu concentration, for low concentrations. Type II, completely desensitizing channels also were activated very rapidly by glu pulses, but their time constant of desensitization was 1–2 ms, and no channel openings were observed after more than 10 ms presence of a high glu concentration. The peak probabilities of channel opening rose with about the 5th power of glu concentration (for low concentrations). Type III, non-desensitizing channels, were observed relatively rarely. They were activated much more slowly and reached much lower probabilities of opening than type I and II channels. They did not show appreciable desensitization. Type IV, short-opening channels, develop sometimes from type I channels while recording, and may revert to the type I. Type IV channels show an additional open time component of 0.08 ms average duration, and a relatively long additional closed time of on average 1.3 ms. In addition to channel measurements, distributions of amplitudes and time courses of macroscopic quantal currents were determined. It is discussed in which way the different channel types may contribute to the quantal currents.     

Analysis of the entire nucleotide sequence of the cryptic plasmid of Chlamydia trachomatis serovar L1. Evidence for involvement in DNA replication.

Chlamydia trachomatis serovar L1/440/LN possesses a 7498bp plasmid which was designated pLGV440. The plasmid was cloned at the BamH1 site of pAT153 into Escherichia coli and the recombinant plasmid was designated pCTL1. A detailed restriction endonuclease map of pCTL1 was constructed. A fragment of the chlamydial plasmid was shown to function as a promoter in E. coli when placed upstream of the lacZ gene. The entire plasmid was sequenced by the chain termination method. Open reading frames were identified from the resulting consensus sequence together with a candidate for the plasmid origin of replication consisting of four perfect tandem repeats of a 22bp sequence, an A:T rich sequence and an open reading frame which could generate a 34.8kdal product. The predicted polypeptide products of the open reading frames were compared by computer with all reported protein sequences. Homology of the predicted polypeptide product of an open reading frame to the E. coli dnaB protein and the analogous product of gene 12 of bacteriophage P22 is described.     

Loss of CNGB1 protein leads to olfactory dysfunction and subciliary cyclic nucleotide-gated channel trapping

Olfactory receptor neurons (ORNs) employ a cyclic nucleotide-gated (CNG) channel to generate a receptor current in response to an odorant-induced rise in cAMP. This channel contains three types of subunits, the principal CNGA2 subunit and two modulatory subunits (CNGA4 and CNGB1b). Here, we have analyzed the functional relevance of CNGB1 for olfaction by gene targeting in mice. Electro-olfactogram responses of CNGB1-deficient (CNGB1-/-) mice displayed a reduced maximal amplitude and decelerated onset and recovery kinetics compared with wild-type mice. In a behavioral test, CNGB1-/- mice exhibited a profoundly decreased olfactory performance. Electrophysiological recordings revealed that ORNs of CNGB1-/- mice weakly expressed a CNG current with decreased cAMP sensitivity, very rapid flicker-gating behavior and no fast modulation by Ca2+-calmodulin. Co-immunoprecipitation confirmed the presence of a CNGA2/CNGA4 channel in the olfactory epithelium of CNGB1-/- mice. This CNGA2/CNGA4 channel was targeted to the plasma membrane of olfactory knobs, but failed to be trafficked into olfactory cilia. Interestingly, we observed a similar trafficking defect in mice deficient for the CNGA4 subunit. In conclusion, these results demonstrate that CNGB1 has a dual function in vivo. First, it endows the olfactory CNG channel with a variety of biophysical properties tailored to the specific requirements of olfactory transduction. Second, together with the CNGA4 subunit, CNGB1 is needed for ciliary targeting of the olfactory CNG channel.