Expression of Odorant Receptor Family, Type 2 OR in the Aquatic Olfactory Cavity of Amphibian Frog Xenopus tropicalis

Recent genome wide in silico analyses discovered a new family (type 2 or family H) of odorant receptors (ORs) in teleost fish and frogs. However, since there is no evidence of the expression of these novel OR genes in olfactory sensory neurons (OSN), it remains unknown if type 2 ORs (OR2) function as odorant receptors. In this study, we examined expression of OR2 genes in the frog Xenopus tropicalis. The overall gene expression pattern is highly complex and differs depending on the gene and developmental stage. RT-PCR analysis in larvae showed that all of the OR2η genes we identified were expressed in the peripheral olfactory system and some were detected in the brain and skin. Whole mount in situ hybridization of the larval olfactory cavity confirmed that at least two OR2η genes so far tested are expressed in the OSN. Because tadpoles are aquatic animals, OR2η genes are probably involved in aquatic olfaction. In adults, OR2η genes are expressed in the nose, brain, and testes to different degrees depending on the genes. OR2η expression in the olfactory system is restricted to the medium cavity, which participates in the detection of water-soluble odorants, suggesting that OR2ηs function as receptors for water-soluble odorants. Moreover, the fact that several OR2ηs are significantly expressed in non-olfactory organs suggests unknown roles in a range of biological processes other than putative odorant receptor functions

Exotic models may offer unique opportunities to decipher specific scientific question: the case of Xenopus olfactory system.

http://onlinelibrary.wiley.com/doi/10.1002/ar.22749/abstract ; http://www.bionity.com/International audienceThe fact that olfactory systems are highly conserved in all animal species from insects to mammals allow the generalization of findings from one species to another. Most of our knowledge about the anatomy and physiology of the olfactory system comes from data obtained in a very limited number of biological models such as rodents, Zebrafish, Drosophila, and a worm, Caenorhabditis elegans. These models have proved useful to answer most questions in the field of olfaction, and thus concentrating on these few models appear to be a pragmatic strategy. However, the diversity of the organization and physiology of the olfactory system amongst phyla appear to be greater than generally assumed and the four models alone may not be sufficient to address all the questions arising from the study of olfaction. In this article, we will illustrate the idea that we should take advantage of biological diversity to address specific scientific questions and will show that the Xenopus olfactory system is a very good model to investigate: first, olfaction in aerial versus aquatic conditions and second, mechanisms underlying postnatal reorganization of the olfactory system especially those controlled by tyroxine hormone. Anat Rec, 296:1453-1461, 2013. © 2013 Wiley Periodicals, Inc

Amino acid sequence identity (%) of <i>X. tropicalis</i> type 2 ORs and class I Ors.

*<p>XtOR1(I)α1: estEXT_fgenesh1.pg.C_5720016.</p>**<p>XtOR1(I)δ1: e_gw1.799.21.1.</p

OR gene expression in adult olfactory cavities.

<p>A: Schematic illustration of the nasal cavities of the adult frog. The MC is filled in water and the PC is open to air. The air flow goes though the PC to the lung. B: The expression of OR2ηs and some OR1s (class I and II) in adult nasal cavities. Quantitative PCR was done for each OR gene and normalized by using the OMP gene, which is expressed in every mature OSN. Most class I ORs were preferentially expressed in the MC. Class I ORα5 was exceptionally expressed at a significant level in the PC as well as the MC. Bars represent standard deviation (n = 3). Note that the expression level of OBP and class II (mix) OR was much higher than each single OR2η and class I OR gene (different scale). Gene ID: OR1α2: ENSXETG00000024801.1, OR1α4: fgenesh1_pg.C_scaffold_1078000009, OR1α5: e_gw1.2098.6.1, OR1β3: fgenesh1_pg.C_scaffold_976000003, OR1β5: e_gw1.976.19.1, OR1δ2: e_gw1.799.9.1, OR1ε4: e_gw1.799.69.1.</p

Phylogenetic tree of <i>X. tropicalis</i> OR1 and OR2 genes.

<p>Amino acid sequences of all XtOR2 and all XtOR1 class I (OR(I)), four XtOR1 class II ORs (OR(II)γ), and three melanocortin receptors (MCRs), were used for the phylogenetic analysis.</p

XtOR2 gene expression in various organs in stage 55 larvae and full-grown adults.

<p>The primer set for class II OR amplified multiple class II OR genes. PCR cycles were adjusted to obtain adequate amounts of the products (35 cycles for OR2 and class I ORs, and 30 cycles for rpL8 and class II ORs).</p

Maitotoxin Induces Acrosome Reaction and Histone Degradation of Starfish Asterina pectinifera Sperm

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