Multiple subcellular localizations of PCTAIRE-1 in brain

We developed a selective antibody to a synthetic peptide corresponding to an N-terminal sequence of the PCTAIRE-1 protein. In rodent brain extracts it recognized only the protein doublet characteristic of PCTAIRE-1, and this signal is completely abolished by preincubation of the antibody with the immunopeptide. Immunolabeling experiments done with this PCTAIRE-1-specific antibody reveal that the protein is widely distributed in the rodent brain as are the mRNAs visualized using an antisense riboprobe corresponding to the entire PCTAIRE-1 open reading frame. Two types of PCTAIRE-1 protein localizations were observed: first a diffuse labeling of almost all brain regions, particularly intense in the molecular layer of the cerebellum and the mossy fiber region of the hippocampus, and second a spot-like localization in the nuclei of large neurons such as cerebellar Purkinje cells and pyramidal cells of the hippocampus. Colocalization with the B23 protein allows one to identify these compartments as nucleoli. Our results suggest a nucleolar function of PCTAIRE-1 in large neurons and a role in regions containing important granule cell projections.