Characterization of the Olfr7 odorant receptor gene cluster.

摘要

The initial step in olfaction involves the interaction of odorant ligands with odorant receptors (ORs) located on the cilia of olfactory sensory neurons. This thesis presents detailed genomic studies of the Olfr7 OR gene cluster, possibly the largest OR gene cluster, in both mouse and human. First, a 129/Sv BAC contig of ∼2 Mb was constructed, from which 37 full length, 2 partial, and 3 pseudo OR genes were cloned and sequenced using a novel approach. A similar C57BL/6 BAC contig was also constructed and sequenced by the NIH Mouse Initiative. With the completion of the mouse and human genome assemblies, the complete Olfr7 OR gene cluster was annotated by homology search in both mouse and human. The mouse cluster contains 128 OR genes, including 30 pseudogenes (23%), in a 2.5 Mb region on chromosome 9. The syntentic region in human contains 45 genes, of which 17 are pseudogenes (37%), in a 1.5 Mb region on chromosome 11q25. Olfr7 OR genes share amino acid identities between 30–97%. Ten mouse and one human Olfr7 OR genes contain an unconventional putative NXC glycosylation sequon at the amino terminus of their protein sequences. The genomic structure of the cluster is well conserved between mouse and human. Members of four distinct gene subfamilies, classified based on phylogeny, are located as blocks in the cluster. Polymorphism studies of 81 Olfr7 OR gene CDS between the 129/Sv and C57BL/6 mouse strains reveal a dichotomous distribution of identical and polymorphic ORs in the cluster. Members of the M30/M31 subfamily appear to have a different evolutionary dynamic from the rest of the Olfr7 genes. Progress towards generating two strains of mutant mice, one in which the entire cluster is deleted, and one with a tandem duplication of the cluster, will provide important tools for genetic, physiological, and behavioral studies in the olfaction field.