Olfactory sensory neuron-specific and sexually dimorphic expression of protocadherin 20.

Olfactory sensory axons navigate from the nasal cavity to the olfactory bulb and sort from among 1,000 different odorant receptor-expressing types to converge upon the same two or three glomeruli. To achieve this task during development, it is likely that multiple classes of regulatory molecules, including cell adhesion molecules, are involved. Cell adhesion molecules have been shown to be important in controlling axon guidance, fasciculation, and synapse formation. To gain further understanding of the involvement of adhesion molecules in olfactory circuitry development, we examined the dynamic and cell type specific expression of a novel protocadherin, PCDH20, in the olfactory system. PCDH20 is specifically expressed in newly differentiated olfactory sensory neurons and their axons during development. PCDH20 expression is down-regulated in the adult olfactory system, except in a small olfactory sensory neuron population. These small, discrete numbers of PCDH20-positive glomeruli in the adult olfactory bulb are consistently clustered in the ventral-caudal region in both male and female mice. However, adult males have higher numbers of PCDH20-positive glomeruli with a broader distribution, whereas adult females have fewer PCDH20-positive glomeruli with a more restricted distribution. The gender difference in PCDH20 expression may reflect olfactory receptor expression differences for gender-specific social discrimination.