Fishes olfactory receptors

The olfactory receptor genes can be considered the first layer of olfactory information processing and in fact they define the nature of odorants, since any molecule becomes an odorant solely by virtue of its interaction with an olfactory receptor. However, not many olfactory receptor genes are currently deorphanized, due to the sheer complexity of the task, and because heterologous expression is inefficient for many olfactory receptors. Consequently, detailed ligand response spectra so far only exist for a handful of mammalian and a single fish olfactory receptor (Luu et al. 2004). 

Irie-Kushiyama S, Asano-Miyoshi M, Suda T, Abe K, Emori Y (2004) Identification of 24 genes and two pseudogenes coding for olfactory receptors in Japanese loach, classified into four subfamilies a putative evolutionary process for fish olfactory receptor genes by comprehensive phylogenetic analysis. Gene 325 123-135... 

Freitag J., Beck A., Ludwig G., von Buchholtz L. and Breer H. (1999). On the origin of the olfactory receptor family receptor genes of the jawless fish (Lampetra fluviatilis). Gene 226, 165-174. 

Hansen A. and Finger T. (2000). Phyletic distribution of crypt-type olfactory receptor neurons in fishes. Brain Behav Evoi 55, 100-110. 

Muller J. and Marc R. (1984). Three distinct morphological classes of receptors in fish olfactory organs. J Comp Neurol 222, 482-495. 

In fish, both taste and olfactory stimuli are waterborne. However, taste involves the seventh, ninth or tenth cranial nerves, in contrast to the first cranial nerve for smell. Elasmobranchs have their taste buds in the mouth and pharynx, but in bony fish they occur around the gills, on barbels and pectoral fins, and also scattered over the rest of the body surface. They crowd particularly in the roof of the mouth, forming the palatal organ. The taste receptor cells are arranged as a bundle to form a taste bud. Like other vertebrates, fish have receptors for sweet, sour, salty, and bitter. For instance, goldfish reject quinine-treated food pellets (Jobling, 1995). Many fish species are particularly sensitive to acidic taste characteristics. The responses of fish to amino acids will be discussed in Chapter 12. 

Niimura Y, Nei M (2005) Evolutionary dynamics of olfactory receptor genes in fishes and tetrap-ods. Proc Natl Acad Sci USA 102 6039-6044... 

Saraiva LR, Korsching SI (2007) A novel olfactory receptor gene family in teleost fish. Genome Res 17 1448-1457... 

Menashe I, Man O, et al. (2003) Different noses for different people. Nat Genet 34(2) 143—4 Mombaerts P (2004) Odorant receptor gene choice in olfactory sensory neurons the one receptor-one neuron hypothesis revisited. Curr Opin Neurobiol 14(1) 31—36 Niimura Y, Nei M (2005) Evolutionary dynamics of olfactory receptor genes in fishes and tetrapods. 

Taken together, the fish olfactory bulb provides for the opportunity to study functionally segregated responses of all olfactory receptor neurons in a recepto-topic map. Due to the small size and semi-transparent nature of the zebrafish olfactory bulb, it is to be expected that odor responses of all three receptor neuron populations could be measured simultaneously and possibly identified by spatial position. Indeed, in the zebrafish olfactory bulb it has been possible to measure odor responses in lateral, medial, and ventral glomeruli (Friedrich and Korsching 1997, 1998). 

The evolutionary path followed in teleost fish development has been distinctly different from that pursued in tetrapods, with massive diversification in the TAAR family but with a total lack of any expansion in the ORA family. It is expected that the respective ligand repertoires and corresponding biological function will turn out to be distinctly different as well. However, extensive progress in deorphanizing teleost olfactory receptors will be necessary to understand the evolution of ligand repertoires for the olfactory receptor gene families. 

Hansen A, Rolen SH, Anderson K, Morita Y, Caprio J, Finger TE (2003) Correlation between olfactory receptor cell type and function in the channel catfish. J Neurosci 23 9328-9339 Hansen A, Anderson KT, Finger TE (2004) Differential distribution of olfactory receptor neurons in goldfish structural and molecular correlates. J Comp Neurol 477 347-359 Hashiguchi Y, Nishida M (2006) Evolution and origin of vomeronasal-type odorant receptor gene repertoire in fishes. BMC Evol Biol 6 76... 

Valentincic T, Miklavc P, Dolenek J, Pliberek K (2005) Correlations between olfactory discrimination, olfactory receptor neuron responses and chemotopy of amino acids in fishes. Chem Senses 30(Suppl l) i312—i314... 

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