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S Firestein

Publications and source records attributed to S Firestein.

At least 19 recordsLinked to original sources
PubMed2001

How the olfactory system makes sense of scents.

The human nose is often considered something of a luxury, but in the rest of the animal world, from bacteria to mammals, detecting chemicals in the environment has been critical to the successful organism. An indication of the importance of olfactory systems is the significant proportion - as much as 4% - of the genomes of many higher eukaryotes that is devoted to encoding the proteins of smell. Growing interest in the detection of diverse compounds at single-molecule levels has made the olfactory system an important system for biological modelling.

Animals↗
PubMed2001

Length analyses of mammalian G-protein-coupled receptors.

G-protein-coupled receptors (GPCRs) play a crucial role in mediating effects of extracellular messengers in a wide variety of biological systems, comprising the largest gene superfamily at least in mammals. Mammalian GPCRs are broadly classified into three families based on pharmacological properties and sequence similarities. These sequence similarities are largely confined to the seven transmembrane domains, and much less in the extracellular and intracellular loops and terminals (LTs). Together with the fact that the LTs vary considerably in length and sequence, the LT length of GPCRs has not been studied systematically. Here we have applied a statistical analysis to the length of the LTs of a wide variety of mammalian GPCRs in order to examine the existence of any trends in molecular architecture among a known mammalian GPCR population. Tree diagrams constructed by cluster analyses, using eight length factors in a given GPCR, revealed possible length relations among GPCRs and defined at least three groups. Most samples in Group J (joined) and Group M (minor) had an exceptionally long N-terminal and I3 loop, respectively; and other samples were considered as Group O (other/original). This length-based classification largely coincided with the conventional sequence- and pharmacology-based classification, suggesting that the LT length contains some biological information when analysed at the population level. Principle component analyses suggested the existence of inherent length differences between loops and terminals as well as between extracellular and intracellular LTs. Wilcoxon rank transformation tests unveiled statistically significant differences between Group O and Group J, not only in the N-terminal and I3 loop, but also in the E3 loop. Correlation analyses identified an E1-I2 length-correlation in Group O and Group J and an N-E3 length-correlation in Group J. Taken together, these results suggest a possible functional importance of LT length in the GPCR superfamily.

Animals↗
PubMed2000

Adenoviral vector-mediated rescue of the OMP-null phenotype in vivo.

The use of gene deletion by homologous recombination to determine gene or protein function has wide application in vertebrate neurobiology. An ideal complement to gene deletion would be subsequent gene replacement to demonstrate re-acquisition of function. Here we used an adenoviral vector to replace the olfactory marker protein (OMP) gene in olfactory receptor neurons of adult OMP-null mice and demonstrated the subsequent re-acquisition of function. Our results show that short-term expression of OMP restores the kinetics of electrophysiological responses of OMP-null mice to those of the control phenotype. This adenoviral-mediated rescue of the OMP-null phenotype is consistent with involvement of OMP in olfactory transduction.

Animals↗
PubMed2000

The molecular receptive range of an odorant receptor.

An odor perception is the brain's interpretation of the activation pattern of many peripheral sensory neurons that are differentially sensitive to a wide variety of odors. The sensitivity of these neurons is determined by which of the thousand or so odor receptor proteins they express on their surface. Understanding the odor code thus requires mapping the receptive range of odorant receptors. We have adopted a pharmacological approach that uses a large and diverse pool of odorous compounds to characterize the molecular receptive field of an odor receptor. We found a high specificity for certain molecular features, but high tolerance for others-a strategy that enables the olfactory apparatus to be both highly discriminating, and able to recognize several thousand odorous compounds.

Aldehydes↗
PubMed1999

Vertebrate odorant receptors.

Olfactory transduction begins with the binding of an odorous molecule to a protein receptor--odorant receptor--on the cell surface of olfactory neuron. Odorant receptors are encoded by a large gene family belonging to the superfamily of G-protein-coupled, seven-transmembrane-domain receptors. Since the identification of the receptor gene family in 1991, a considerable amount of progress has been made in the study of odorant receptors, including aspects of spatial and temporal expression pattern, the genomic organization of the receptor genes, regulation of expression, and receptor function. These studies are of critical importance in understanding how the olfactory system recognizes and distinguishes thousands of odors.

Animals↗
PubMed1999

Segregated expression of neurestin in the developing olfactory bulb.

Neurestin is a putative transmembrane protein whose expression is developmentally regulated in neurons. Here we examined neurestin expression pattern in mitral/tufted cells in the developing rat olfactory bulb. In the main olfactory bulb, neurestin expression was segregated in the dorso-rostral area and in the ventro-caudal area, but not in between. In the accessory olfactory bulb, neurestin expression was found only in the far caudal area. This area did not completely correspond to a caudal half of the vomeronasal nerve and glomerular layers positive for a G-protein Go alpha. These spatio-temporal expression patterns suggest that neurestin functions as a target recognition molecule that specifies zonal projection patterns of olfactory and vomeronasal sensory neurons.

Animals↗
PubMed1999

Neurestin: putative transmembrane molecule implicated in neuronal development.

We have cloned a novel cDNA encoding a putative transmembrane protein, neurestin, from the rat olfactory bulb. Neurestin was identified based on a sequence similar to that of the second extracellular loops of odorant receptors in the cysteine-rich CC box located immediately after EGF-like motifs. Neurestin shows homology to a neuregulin gene product, human gamma-heregulin, a Drosophila receptor-type pair-rule gene product, Odd Oz (Odz) / Ten(m), and Ten(a), suggesting a possible function in synapse formation and morphogenesis. Recently, a mouse neurestin homolog has independently been cloned as DOC4 from the NIH-3T3 cell line. Northern blot analysis showed that neurestin is highly expressed in the brain and also in other tissues at much lower levels. In situ hybridization studies showed that neurestin is expressed in many types of neurons, including pyramidal cells in the cerebral cortex and tufted cells in the olfactory bulb during development. In adults, neurestin is mainly expressed in olfactory and hippocampal granule cells, which are known to be generated throughout adulthood. Nonetheless, in adults the expression of neurestin was experimentally induced in external tufted cells during regeneration of olfactory sensory neurons. These results suggest a role for neurestin in neuronal development and regeneration in the central nervous system.

Amino Acid Sequence↗
PubMed1999

Cyclic nucleotide-gated channels. Molecular mechanisms of activation.

Activation of cyclic nucleotide-gated (CNG) channels represents the final step in the transduction pathways in both vision and olfaction. Over the past several years, CNG channels have been found in a variety of other cell types where they might fulfill various physiological functions. The olfactory and photoreceptor CNG channels rely on the binding of at least two molecules of cAMP or cGMP at intracellular sites on the channel protein to open a nonspecific cation conductance with a significant permeability to Ca ions. A series of elegant experiments with cloned channels and chimeric constructs has revealed significant information regarding the binding and gating reactions that lead to CNG channel activation. These recent studies have identified several regions as well as specific amino acid residues distributed on the retinal or the olfactory CNG channel subunits that play a key role in channel regulation. In this review, we will focus on these specific molecular sites of activation and modulation of CNG channels.

Animals↗
PubMed1998

Functional expression of a mammalian odorant receptor.

Candidate mammalian odorant receptors were first cloned some 6 years ago. The physiological function of these receptors in initiating transduction in olfactory receptor neurons remains to be established. Here, a recombinant adenovirus was used to drive expression of a particular receptor gene in an increased number of sensory neurons in the rat olfactory epithelium. Electrophysiological recording showed that increased expression of a single gene led to greater sensitivity to a small subset of odorants.

Adenoviridae↗
PubMed1997

Beta subunits of the olfactory cyclic nucleotide-gated channel form a nitric oxide activated Ca2+ channel.

Cyclic nucleotide-gated channels are important in visual and olfactory transduction, and possibly in other neuronal functions. These channels have a complex permeability to Ca2+ ions that may be important in their cellular functions. They are composed of two different subunits, alpha and beta, that have been cloned and expressed, but the beta subunit alone cannot be activated by cyclic nucleotides, confounding the analysis of its characteristics. However, we found that nitric oxide can activate the homomeric expressed beta subunit, and the resulting channel possesses many properties of the L-type Ca2+ channels, including high permeability to Ca2+ ions and sensitivity to Ca2+ channel blockers. Thus, the Ca2+ permeability characteristics of native channels are mostly conferred by properties of the beta subunit, and the beta subunit alone can act as a NO-sensitive Ca2+ channel. A nearly identical conductance activated by NO is present in the membrane of rat vomeronasal neurons, indicating that homomeric beta channels exist in vivo.

Animals↗
PubMed1996

Olfaction: scents and sensibility.

Expression of a receptor protein has, for the first time, been definitively correlated with sensitivity to a particular odorant. This receptor, expressed in the nematode Caenorhabditis elegans, appears to be distinct from the putative vertebrate odorant receptors.

Animals↗
PubMed1996

Gaseous second messengers in vertebrate olfaction.

Gaseous monoxides such as nitric oxide (NO) and carbon monoxide (CO) are now recognized as important messengers in the nervous system. The enzymes generating these compounds are highly expressed in the olfactory system, including the epithelium and the main and accessory bulbs. Although the physiological roles of these molecules is still not entirely clear, some important new data has recently emerged. Alternate pathways for NO action, possible interactions between NO, CO, and intermediate proteins, and evidence suggestive of important roles for these molecules in development and regeneration are reviewed here. Of particular interest is the possible modulatory role of NO or CO in the transduction process, an area in which there has been an explosive growth in new data. Although it is clear that NO and CO are integral to the functioning of the olfactory system, it is equally obvious that many of the potential roles have yet to be clearly defined.

Animals↗
PubMed1996

Adenovirus-mediated gene transfer in olfactory neurons in vivo.

We used recombinant adenoviruses as a means of expressing exogenous genes in olfactory neurons in vivo. A replication incompetent adenovirus (type 5, Ad5) carrying the reporter gene lacZ, which codes for the enzyme beta-galactosidase (beta-Gal), was applied in solution to the olfactory epithelia of rats. The expression of lacZ was controlled by the cytomegalovirus immediate-early promoter/enhancer. beta-Gal expression was observed 1 day postinfection and was maximal at 3-10 days, although it could be detected for at least 21 days postinfection. Expression patterns were heterogeneous, ranging from a few percent to over 25% of the cells in different regions of both turbinate and septal epithelium. Staining was stronger in the olfactory versus respiratory epithelia. In olfactory epithelium staining was almost entirely restricted to olfactory neurons. beta-Gal staining was also observed in the olfactory axons so that nerve bundles could be traced to their targets in the glomerular layer of the olfactory bulb. Intense staining of some glomeruli was evident as long as 21 days postinfection. There was no evidence of cell loss or tissue damage due to viral infection. These results demonstrate that it is possible to use recombinant Ad5 for expressing foreign genes in olfactory neurons. This technique could be used in olfactory neurons to increase expression levels of olfactory specific genes, including the odor receptor, putative guidance and growth molecules, or elements of the transduction cascade, in order to elucidate their biological functions in vivo.

Adenoviridae↗
PubMed1996

Direct activation of the olfactory cyclic nucleotide-gated channel through modification of sulfhydryl groups by NO compounds.

The activation of a cyclic nucleotide-gated channel is the final step in sensory transduction in olfaction. Normally, this channel is opened by the intracellular cyclic nucleotide second messenger cAMP or cGMP. However, in single channel recordings we found that donors of nitric oxide, a putative intercellular messenger, could directly activate the native olfactory neuron channel. Its action was independent of the presence of the normal ligand and did not involve the cyclic nucleotide binding site, suggesting an alternate site on the molecule that is critical in channel gating. The biochemical pathway appears to utilize nitric oxide in one of its alternate redox states, the nitrosonium ion, transnitrosylating a free sulfhydryl group belonging to a cysteine residue tentatively identified as being in the region linking the S6 transmembrane domain to the ligand binding domain.

Ambystoma↗