OLFACTION IN BIRDS - DIFFERENTIAL EMBRYONIC EXPRESSION OF 9 PUTATIVE ODORANT RECEPTOR GENES IN THE AVIAN OLFACTORY SYSTEM

We have isolated nine putative odorant receptor genes from the chick, named COR1 to COR9, that belong to the large multigene family of olfac tory G protein-coupled receptors found in the fish, rat, mouse, dog, a nd human. By combining genomic DNA blot analysis, low stringency libra ry screenings, and several PCR analyses, we were able to detect simila r to 20 COR genes in the chick genome highly related to COR1-9. By in situ hybridization of newborn and adult, COR expression was detected o nly in the olfactory epithelium, and exhibited a random spatial distri bution. During development, COR expression was observed as early as em bryonic stage E5. Different levels of gene expression were observed fo r the COR1-9 genes: at E5, COR1-6 expression was high compared to the expression of COR7, COR8, and COR9. Surprisingly, at E5, a row of COR1 -6 positive cells probably associated with the olfactory nerve extende d outside the olfactory placode, reaching the anterior pole of the dev eloping forebrain. These results suggest that, in addition to their ro le as putative odorant receptors, some COR may play a role in the deve lopment of the avian olfactory system.