Title: The Role of the Clustered Protocadherins in the Assembly of Olfactory Neural Circuits
Description: The clustered protocadherins (Pcdh α, β & γ) provide individual neurons with cell surface diversity. However, the importance of Pcdh mediated diversity in neural circuit assembly and how it may promote neuronal connectivity remains largely unknown. Moreover, to date, Pcdh in vivo function has been studied at the level of individual gene clusters; whole cluster-wide function has not been addressed. Here I examine the role of all three Pcdh gene clusters in olfactory sensory neurons (OSNs); a neuronal type that expressed all three types of Pcdhs and in addition I address the role of Pcdh mediate diversity in their wiring. When OSNs share a dominant single Pcdh identity (α, β & γ) their axons fail to form distinct glomeruli, suggestive of inappropriate self-recognition of neighboring axons (loss of non-self-discrimination). By contrast, deletion of the entire α, β,γ Pcdh gene cluster, but not of each individual cluster alone, leads to loss of self-recognition and self-avoidance thus, OSN axons fail to properly arborize.

I conclude that Pcdh-expression is necessary for self-recognition in OSNs, whereas its diversity allows distinction between self and non-self. Both of these functions are required for OSNs to connect and assembly into functional circuits in the olfactory bulb. My results, also reveal neuron-type specific differences in the requirement of specific Pcdh gene clusters and demonstrate significant redundancy between Pcdh isoforms in the olfactory system.