Meeting Abstract

7.1  Monday, Jan. 4  Still smelling after 550 million years; the amphioxus (Branchiostoma floridae) genome encodes orthologs of vertebrate odorant receptors CHURCHER, Allison M.*; TAYLOR, John S.; Univ. of Victoria; Univ. of Victoria amchurch@uvic.ca

A common feature of chemosensory systems is the involvement of G protein-coupled receptors (GPCRs) in the detection of chemical stimuli. In vertebrates, the odorant receptor (OR) repertoires range from 44 genes in pufferfish to over 1000 in some mammals yet there is no evidence that these genes are related to the chemosensory genes found in invertebrates. Using vertebrate OR sequences as queries and a combination of bioinformatics tools, we identified 50 full-length odorant receptors in the cephalochordate (Branchiostoma floridae) all of which form a monophyletic clade with the vertebrate ORs. The majority of the B. floridae ORs are intronless genes and many are tandemly arrayed in the genome as is the case with vertebrate ORs. Comparative sequence analysis combined with searches of OR and non-OR databases revealed three OR-specific amino acid motifs common in cephalochordate, fish and mammalian ORs. The locations of these motifs within the intracellular loops of the protein suggest they are important for maintaining receptor conformation and regulating receptor activity. The identification of OR-specific motifs provides a new set of candidate sites for functional analysis. Moreover, the discovery that B. floridae has orthologs of vertebrate ORs demonstrates that the receptors, and perhaps other components of vertebrate olfaction, evolved at least 550 million years ago. We anticipate our results will lead to an improved understanding of OR gene family evolution, OR gene function, mechanisms that control cell-specific expression, axonal guidance, signal transduction and signal integration.