title: Characterizing the expression of the human olfactory receptor gene family using a novel DNA microarray.
abstract: BACKGROUND
  Olfactory receptor (OR) genes were discovered more than a decade ago, when Buck and Axel observed that, in rats, certain G-protein coupled receptors are expressed exclusively in the olfactory epithelium. Subsequently, protein sequence similarity was used to identify entire OR gene repertoires of a number of mammalian species, but only in mouse were these predictions followed up by expression studies in olfactory epithelium. To rectify this, we have developed a DNA microarray that contains probes for most predicted human OR loci and used that array to examine OR gene expression profiles in olfactory epithelium tissues from three individuals.
  
  
  RESULTS
  We detected expression of 437 (76%) human OR genes in these olfactory epithelia. Interestingly, we detected widespread expression of OR pseudogenes, an observation that may shed light on the mechanism of OR gene choice in the olfactory sensory neurons. To address the hypothesis that OR genes may carry out additional functions, we also characterized the expression of OR genes in a number of non-olfactory tissues.
  
  
  CONCLUSIONS
  While our results corroborate the functional annotation of the majority of predicted human odorant receptors, we find that a large number of putative human OR genes are expressed in non-olfactory tissues, sometimes exclusively so. Our evolutionary analysis of ectopically expressed human OR genes does not lend support to the hypothesis that these genes have alternative functions.
authors.affiliation: Department of Biological Sciences, Columbia University, New York, NY 10027, USA. xz2021@columbia.edu
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Zhang
authors.forename: Omar
authors.initials: O
authors.lastname: De la Cruz
authors.forename: Jayant M
authors.initials: JM
authors.lastname: Pinto
authors.forename: Dan
authors.initials: D
authors.lastname: Nicolae
authors.forename: Stuart
authors.initials: S
authors.lastname: Firestein
authors.forename: Yoav
authors.initials: Y
authors.lastname: Gilad
mesh_terms: D002828:Choristoma; D020869:Gene Expression Profiling / Q000379:methods; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D009831:Olfactory Mucosa; D020411:Oligonucleotide Array Sequence Analysis; D011544:Pseudogenes; D018035:Receptors, Odorant / Q000235:genetics*
chemical_list: D018035:Receptors, Odorant