The vertebrate clustered protocadherin (Pcdh) cell surface proteins are encoded 
by three closely linked gene clusters (Pcdhα, Pcdhβ, and Pcdhγ). Here, we show 
that all three gene clusters functionally cooperate to provide individual mouse 
olfactory sensory neurons (OSNs) with the cell surface diversity required for 
their assembly into distinct glomeruli in the olfactory bulb. Although deletion 
of individual Pcdh clusters had subtle phenotypic consequences, the loss of all 
three clusters (tricluster deletion) led to a severe axonal arborization defect 
and loss of self-avoidance. By contrast, when endogenous Pcdh diversity is 
overridden by the expression of a single-tricluster gene repertoire (α and β and 
γ), OSN axons fail to converge to form glomeruli, likely owing to 
contact-mediated repulsion between axons expressing identical combinations of 
Pcdh isoforms.