PQBP-1 is expressed predominantly in the central nervous system during development

Summary Mutations of PQBP‐1 (polyglutamine binding protein‐1) have been shown recently to cause human mental retardation accompanied by microcephaly at a high frequency. As a first step towards understanding the molecular basis of this developmental anomaly, we analysed developmental expression of PQBP‐1 by in situ hybridization, immunohistochemsitry and Western blot analysis. Although it had been shown by Northern blot analysis that PQBP‐1 mRNA is expressed in multiple organs in adult mice, our present results revealed that PQBP‐1 mRNA and protein are dominantly expressed in the central nervous system (CNS) in embryos and in newborn mice. The mean expression level of PQBP‐1 reaches a peak around birth and is down‐regulated in adulthood. Furthermore, the expression pattern in the CNS changes remarkably following birth. PQBP‐1 mRNA in the cerebral cortex is high in embryos but it rapidly decreases after birth. PQBP‐1 mRNA increases in external and internal granular cell layers of the cerebellum from postnatal day 1 (P1) to P5. In addition, expression in the subventricular zone, where neurogenesis occurs, was high from P5 to adulthood. Collectively, these findings suggest that PQBP‐1 might be involved in neuronal proliferation and/or maturation. These ideas may be relevant to the insufficient growth of brain structure reported in PQBP‐1‐linked human mental retardation.