Odorant binding protein diversity and distribution among the insect orders, as indicated by LAP, an OBP-related protein of the true bug Lygus lineolaris (Hemiptera, Heteroptera).
(17/920)
Insect odorant binding proteins (OBPs) are thought to deliver odors to olfactory receptors, and thus may be the first biochemical step in odor reception capable of some level of odor discrimination. OBPs have been identified from numerous species of several insect orders, including Lepidoptera, Diptera, Coleoptera and Hymenoptera; all are holometabolous insects belonging to the monophyletic division of insects known as the Endopterygota. Recently, an antennal protein with OBP-like properties was identified from Lygus lineolaris, a hemipteran insect representing the Hemipteroid Assemblage, a sister division to the Endopterygota. The full length sequence of Lygus antennal protein (LAP) is presented in this report. In situ hybridization analysis revealed LAP expression in cell clusters associating with olfactory sensilla; expression was adult-specific, initiating in developing adult tissue during the transitional period that precedes the actual adult molt. Sequence analysis confirmed that LAP is homologous with the OBP-related protein family, and most similar to the OS-E and OS-F proteins of Drosophila, the ABPX proteins of Lepidoptera and the OBPRP proteins of the Coleoptera. Assuming that the OBP-related proteins represent one homologous family, the identification of LAP significantly expands the phylogenetic depth of that family and its underlying role in odor detection to encompass all members of the Endopterygota and Hemipteroid Assemblage, which comprise >90% of all insect species. (+info)
A kinetic model of the transient phase in the response of olfactory receptor neurons.
(18/920)
A model is presented that predicts the instantaneous spike rate of an olfactory receptor neuron (ORN) in response to the quality and concentration of an odor stimulus. The model accounts for the chemical kinetics of ligand-receptor binding and activation processes, and implicitly the initiation of second messenger cascades that lead to depolarization and/or hyperpolarization of the ORN membrane. Both of these polarizing processes are included in the most general form of the model, as well as a process that restores the voltage to its negative resting state. The spike rate is assumed to be linearly proportional to the level of voltage depolarization above a critical negative voltage level. The model includes the simplifying assumption that activation of bound ligand-receptor complexes by G-proteins and other enabling molecules follows a Monod function that has the ratio of enabling molecules to bound unactivated ligand-receptor complexes as its argument. Parameters are selected that provide an excellent fit of the model to previously published empirical data on the response of cockroach ORNs to pulsed 1-hexanol stimuli. The sensitivity of model output to various model parameters is investigated and changes to parameters are discussed that would improve the ability of ORNs to follow rapidly pulsed stimuli. (+info)
A novel human odorant-binding protein gene family resulting from genomic duplicons at 9q34: differential expression in the oral and genital spheres.
(19/920)
Lipocalins are carrier proteins for hydrophobic molecules in many biological fluids. In the oral sphere (nasal mucus, saliva, tears), they have an environmental biosensor function and are involved in the detection of odours and pheromones. Herein, we report the first identification of human lipocalins involved in odorant binding. They correspond to a gene family located on human chromosome 9q34 produced by genomic duplications: two new odorant-binding protein genes ( hOBP (IIa) and hOBP (IIb) ), the previously described tear lipocalin LCN1 gene and two new LCN1 pseudogenes. Although 95% similar in sequence, the two hOBP (II) genes were differentially expressed in secretory structures. hOBP (IIa) was strongly expressed in the nasal structures, salivary and lachrymal glands, and lung, therefore having an oral sphere profile. hOBP (IIb) was more strongly expressed in genital sphere organs such as the prostate and mammary glands. Both were expressed in the male deferent ducts and placenta. Surprisingly, alternatively spliced mRNAs resulting in proteins with different C-termini were generated from each of the two genes. The single LCN1 gene in humans generated a putative odorant-binding protein in nasal structures. Finally, based on the proposed successive genomic duplication history, we demonstrated the recruitment of exons within intronic DNA generating diversity. This is consistent with a positive selection pressure in vertebrate evolution in the intron-late hypothesis. (+info)
Relationships between odor-elicited oscillations in the salamander olfactory epithelium and olfactory bulb.
(20/920)
Oscillations in neuronal population activity, or the synchronous neuronal spiking that underlies them, are thought to play a functional role in sensory processing in the CNS. In the olfactory system, stimulus-induced oscillations are observed both in central processing areas and in the peripheral receptor epithelium. To examine the relationship between these peripheral and central oscillations, we recorded local field potentials simultaneously from the olfactory epithelium and olfactory bulb in tiger salamanders (Ambystoma tigrinum). Stimulus-induced oscillations recorded at these two sites were matched in frequency and slowed concurrently over the time course of the response, suggesting that the oscillations share a common source or are modulated together. Both the power and duration of oscillations increased over a range of amyl acetate concentrations from 2.5 x 10(-2) to 1 x 10(-1) dilution of saturated vapor, but peak frequency was not affected. The frequency of the oscillation did vary with different odorant compounds in both olfactory epithelium and bulb (OE and OB): amyl acetate, ethyl fenchol and d-carvone elicited oscillations of significantly different frequencies, and there was no difference in OE and OB oscillation frequencies. No change in the power or frequency of OE oscillations was observed after sectioning the olfactory nerve, indicating that the OE oscillations have a peripheral source. Finally, application of 1.0 and 10 microM tetrodotoxin to the epithelium blocked OE oscillations in a dose-dependent and reversible manner, suggesting that peripheral olfactory oscillations are related to receptor neuron spiking. (+info)
The large srh family of chemoreceptor genes in Caenorhabditis nematodes reveals processes of genome evolution involving large duplications and deletions and intron gains and losses.
(21/920)
The srh family of chemoreceptors in the nematode Caenorhabditis elegans is very large, containing 214 genes and 90 pseudogenes. It is related to the str, stl, and srd families of seven-transmembrane or serpentine receptors. Like these three families, most srh genes are concentrated on chromosome V, and mapping of their chromosomal locations on a phylogenetic tree reveals 27 different movements of genes to other chromosomes. Mapping of intron gains and losses onto the phylogenetic tree reveals that the last common ancestral gene of the family had five introns, which are inferred to have been lost 70 times independently during evolution of the family. In addition, seven intron gains are revealed, three of which are fairly recent. Comparisons with 20 family members in the C. briggsae genome confirms these patterns, including two intron losses in C. briggsae since the species split. There are 14 clear C. elegans orthologs for these 20 genes, whose average amino acid divergence of 68% allows estimation of 85 gene duplications in the C. elegans lineage since the species split. The absence of six orthologs in C. elegans also indicates that gene loss occurs; consideration of all deletions and terminal truncations of srh pseudogenes reveals that large deletions are common. Together these observations provide insight into the evolutionary dynamics of this compact animal genome. (+info)
Regulation of cutaneous allergic reaction by odorant inhalation.
(22/920)
Olfactory stimuli modulate emotional conditions and the whole body immune system. Effects of odorant inhalation on cutaneous immune reaction were examined. Contact hypersensitivity to 2,4, 6-trinitrochlorobenzene was elicited in C57BL/6 mice. The reaction was suppressed at both the induction and elicitation phases by exposure to an odorant, citralva. Topical application of citralva or lyral/lilial did not affect the reaction. The suppressive effect of citralva was more potent than that of another odorant, lyral/lilial. Citralva decreased the number of epidermal Langerhans cells, whereas lyral/lilial had a weak effect. Citralva but not lyral/lilial induced plasma corticosterone. Glucocorticoid receptor antagonist abrogated the suppressive effect of citralva on contact hypersensitivity. Serum interleukin-12 was downregulated by exposure to citralva or lyral/lilial. These data demonstrate that olfactory stimuli regulate the cutaneous immune system. (+info)
To make the most of a small number of neurons, the nematode olfactory system includes neurons that are bilaterally symmetrical in morphology, but differ in the sets of genes they express. An intriguing recent example is the axon contact-mediated asymmetry in expression of the str-2 odorant receptor gene. (+info)
Peripheral odor coding in the rat and frog: quality and intensity specification.
(24/920)
In mammals, two recent studies have shown recently that one odor molecule can be recognized by several molecular olfactory receptors (ORs), and a single OR can recognize multiple odor molecules. In addition, one olfactory receptor neuron (ORN) may respond to different stimuli chosen as representative of distinct odor qualities. The aim of the present study was to analyze quality and intensity coding abilities of rat single ORNs, comparing them with previous extensive data gathered in the frog to get insight into the generality of olfactory coding mechanisms over vertebrates. Response properties of 90 rat ORNs to different odors or to one odor at different concentrations were analyzed. In the rat and the frog, odor quality appears to be specified through the identity of activated ORNs. However, rat ORNs have higher response thresholds. This lower sensitivity may be interpreted as an increase in selectivity of rat ORNs for low or medium odor intensities. In these conditions, the lower proportion of activated ORNs could be counterbalanced by their number, as well as by their higher glomerular convergence ratio in the olfactory bulb. From amphibians to mammals, the olfactory system appears to use universal mechanisms based on a combinatorial-coding mode that may allow quasi-infinite possibilities of adaptation to various olfactory environments. (+info)