Phospholipase Cbeta4 expression identifies a novel subset of unipolar brush cells in the adult mouse cerebellum.

Unipolar brush cells (UBCs) are glutamatergic cerebellar interneurons of the granular layer. Previous studies have shown that there are two distinct subsets of UBCs present in the mice cerebellar cortex: calcium-binding protein calretinin (CR) positive and metabotropic glutamate receptor (mGluR)1alpha positive. In this study, we identify phospholipase C (PLC) beta4 as an antigenic marker of a novel subset of UBCs. Double immunolabeling reveals that none of the CR+ subset expresses PLCbeta4. In contrast, most members of the mGluR1alpha subset also express PLCbeta4. In addition, 65% of the PLCbeta4+ subset does not express mGluR1alpha. Thus, there are three distinct UBC subsets in the mouse cerebellum: CR+/PLCbeta4-/mGluR1alpha-, PLCbeta4+/mGluR1alpha-/CR-, and mGluR1alpha+/PLCbeta4+/CR-. Each has a different topographical distribution, both between lobules and mediolaterally within the vermis. The development of PLCbeta4 expression in UBCs is exclusively postnatal--first seen only at P12 and mature at about 3 weeks. A distinct subset of PLCbeta4+ UBCs is also present in primary cerebellar cultures.