Unipolar brush cells (UBCs) are excitatory interneurons with their somata 
located in the granular layer. Recently, T-brain factor 2 (Tbr2) was shown to be 
expressed in a subset of UBCs in mouse cerebellum. Scrambler mice exhibit severe 
cerebellum abnormalities, including the failure of embryonic Purkinje cell 
dispersal and a complete absence of foliation due to a mutation in the 
disabled-1 adaptor protein. Since most UBC markers are expressed postnatally, it 
has proven difficult to identify the relationship between developing Purkinje 
cell clusters and migrating UBCs. Because scrambler mice closely mimic normal 
embryonic day 18 cerebellum, we examined whether Tbr2-positive UBCs are 
associated with Purkinje cell cluster markers such as zebrin II, which is the 
most studied compartmentation marker in the cerebellum. We investigated the 
distribution of Tbr2-positive UBCs in this mutant by using anti-Tbr2 
immunocytochemistry. The data revealed that Tbr2 immunoreactivity was 
exclusively present in the nucleus of UBCs in scrambler cerebellum. Based on 
expression data, a Tbr2-positive UBC map was constructed. In addition, 
Tbr2-positive UBCs are found associated with ectopic zebrin II-immunoreactive 
Purkinje cell clusters in scrambler cerebellum. These data suggest that UBCs use 
Purkinje cell compartmentation to migrate into their final position through 
interactions with the embryonic array of specific Purkinje cell subtypes.