Concurrent expression of recombination activating genes 1 and 2 in zebrafish olfactory sensory neurons

Each olfactory sensory neuron (OSN) expresses a single odorant receptor (OR ) from a large repertoire of clustered OR genes. It has been hypothesized t hat OR gene regulation may involve stochastic DNA rearrangement, which in l ymphocytes requires the recombination activating genes, rag1 and rag2, We h ave recently demonstrated that rag1 is expressed in zebrafish OSNs, Here we report that rag2, the obligate partner for rag1 function, is also expresse d in OSNs and that its expression pattern mimics that of rag1. The onset of rag1 and rag2 expression preceded that of known zebrafish ORs and the numb er of rag1-positive OSNs corresponded with the number expressing the olfact ory cyclic nucleotide-gated cation channel, an OSN marker, Zebrafish OSNs a re the first example of concurrent rag expression in a nonlymphoid tissue. The expression of rag1 and rag2 in OSNs adds to the list of similarities be tween the olfactory and immune systems that includes monoallelic and mutual ly exclusive gene expression. (C) 2001 Wiley-Liss, Inc.