TARGET-INDEPENDENT PATTERN SPECIFICATION IN THE OLFACTORY EPITHELIUM

In mammals, odors are detected by similar to 1000 different types of o dorant receptors (ORs), each expressed by a fraction of neurons in the olfactory epithelium. Neurons expressing a given OR are confined to o ne of four spatial zones but are distributed randomly throughout that zone. In the olfactory bulb, the axons of neurons expressing different ORs synapse at different sites, giving rise to a highly organized and stereotyped information map. An important issue is whether the epithe lial and bulbar maps evolve independently or are linked, for example, by retrograde influences of the bulb on the epithelium. Here we examin ed the onset of expression and patterning of genes encoding ORs and se nsory transduction molecules during mouse embryogenesis and in mice la cking olfactory bulbs. Our results argue for an independent developmen t of epithelial and bulbar maps and an early functional development th at may be pertinent to pattern development in the olfactory bulb.