A novel human odorant-binding protein gene family resulting from genomic duplicons at 9q34: differential expression in the oral and genital spheres

Lipocalins are carrier proteins for hydrophobic molecules in many biological fluids. In the oral sphere (nasal mucus, saliva, tears), they have an environmental biosensor function and are involved in the detection of odours and pheromones, Herein, we report the first identification of human lipocalins involved in odorant binding. They correspond to a gene family located on human chromosome 9q34 produced by genomic duplications: two new odorant-binding protein genes (hOSP(IIa) and hOBP(IIb)), the previously described tear lipocalin LCN1 gene and two new LCN1 pseudogenes. Although 95% similar in sequence, the two hOBP(II) genes were differentially expressed in secretory structures. hOBP(IIa) was strongly expressed in the nasal structures, salivary and lachrymal glands, and lung, therefore having an oral sphere profile, hOBP(IIb) was more strongly expressed in genital sphere organs such as the prostate and mammary glands. Both were expressed in the male deferent ducts and placenta. Surprisingly, alternatively spliced mRNAs resulting in proteins with different C-termini were generated from each of the two genes. The single LCN1 gene in humans generated a putative odorant-binding protein in nasal structures. Finally, based on the proposed successive genomic duplication history, we demonstrated the recruitment of exons within intronic DNA generating diversity. This is consistent with a positive selection pressure in vertebrate evolution in the intron-late hypothesis.