ABSTRACT
A coordinated expression of tissue- and cell-specific genes during development is required to establish the complex functional organization of the vertebrate olfactory system. Owing to the unique features of its olfactory system and the well-characterized phases of its development, Xenopus laevis was chosen as a model organism to study the onset and the temporal and spatial patterns of expression of olfactory-specific genes. Using RT-PCR and in situ hybridization, it was found that expression of Xenopus olfactory marker protein and of class I receptors, which are thought to be responsible for the perception of water-soluble odorants, was detectable as early as stage 32, less than 2 days after fertilization. In contrast, expression of class II receptors, which are thought to recognize airborne odours, was not detected before stage 49, approximately 12 days after fertilization. The results indicate that the expression of olfactory receptors and marker protein is governed by temporally regulated cues during development.
Subject(s)
Olfactory Receptor Neurons/growth & development , Xenopus laevis/growth & development , Animals , Base Sequence , DNA Primers/genetics , Gene Expression Regulation, Developmental , In Situ Hybridization , Olfactory Receptor Neurons/embryology , Olfactory Receptor Neurons/physiology , RNA, Messenger/genetics , RNA, Messenger/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Xenopus laevis/embryology , Xenopus laevis/geneticsABSTRACT
The effects of unilateral olfactory bulb ablation upon the odorant receptor expression were studied during the degeneration/regeneration process in the olfactory epithelium of adult rats. Using the in situ hybridization approach, we compared the time course of decay and recovery of expression for three different receptor subtypes (OR14, OR5, OR124). The number of neurons expressing receptor subtypes dramatically decreased in the olfactory epithelium on the lesioned side and reached a minimum at day 5 postsurgery. A progressive recovery was then observed from day 5 to day 15 postlesion, when a plateau was reached. Noticeable differences in the recovery level of receptor expression were observed according to the zonal patterning: the recovery level for neurons located in the lateral zone reached 70% of the control side value while the recovery levels in the dorsal and medial zones represented 35% and 53% of this value, respectively. Axotomy experiments suggest that zone-specific differences in receptor reexpression reported after bulbectomy might be related to the trophic influence of the olfactory bulb.
Subject(s)
Olfactory Bulb/physiology , Olfactory Receptor Neurons/metabolism , Receptors, Odorant/biosynthesis , Animals , Functional Laterality , In Situ Hybridization , Male , Olfactory Mucosa/chemistry , Olfactory Mucosa/cytology , Postoperative Period , Rats , Rats, Wistar , Receptors, Odorant/geneticsABSTRACT
PCR-approaches with degenerated oligonucleotide primers have been employed in trying to identify novel members of the G-protein coupled receptor (GPCR) superfamily from rat brain. Screening a rat brain library with an amplification product showing some features of a GPCR gene led to the isolation of a full-length clone (RA1c); the encoded polypeptide comprises seven distinct hydrophobic stretches as well as several other hallmarks of GPCRs. Sequence comparison revealed a rather low but significant homology to GPCRs; RA1c shares about 30% sequence identity with various olfactory receptors and about 27% with several peptide receptors. By Northern blot and especially by in situ hybridization analysis it could be demonstrated that the RA1c receptor is expressed only in very distinct areas of the brain and in addition in a defined zone of the olfactory epithelium.
Subject(s)
Brain/metabolism , GTP-Binding Proteins/metabolism , Receptors, Cell Surface/genetics , Receptors, G-Protein-Coupled , Receptors, Odorant/genetics , Amino Acid Sequence , Animals , Base Sequence , Blotting, Northern , Blotting, Southern , Cloning, Molecular , In Situ Hybridization , Molecular Sequence Data , RNA, Messenger/genetics , Rats , Receptors, Cell Surface/metabolism , Receptors, Odorant/metabolismABSTRACT
The laminar segregation of sensory neurons expressing a distinct receptor type was determined in tissue sections through the olfactory epithelium by in situ hybridization employing receptor-specific probes. Reactive cells were restricted to the mid-zone of the epithelium, the location of mature neurons. Detailed analyses revealed that neurons expressing a distinct receptor type were distributed in a characteristic manner throughout the layers of the neuronal zone, i.e. they were preferentially located in a particular laminar zone of the epithelium. Cells expressing different receptor types displayed different distribution patterns. In addition, sets of several reactive neurons within the same laminar zone were found to be arranged in an orderly fashion and were positioned at well-defined intervals. These results indicate that the localization of sensory neurons expressing a distinct receptor type is under stringent control leading to characteristic expression patterns.
