Expression of proliferating cell nuclear antigen (PCNA) in the adult and developing mouse nervous system

Proliferating cell nuclear antigen (PCNA) is essential for the function of DNA polymerases delta and epsilon. Because proliferating cell nuclear antigen is required for DNA replication and repair, PCNA is abundantly expressed in proliferating cells. Interestingly, PCNA mRNA has also been detected in the adult mouse brain by Northern blot analysis. In this study, two monoclonal antibodies against PCNA, PC10 and 19F4, were used for Western blot analysis. Monoclonal antibody PC10, but not 19F4, detected a band in the adult mouse brain extract. This PC10-reactive protein in the brain displayed a more acidic isoelectric point than PCNA by two-dimensional gel electrophoresis. In situ hybridization showed that PCNA mRNA was abundantly expressed in the adult mouse subventricular zone. Additionally, relatively low levels of PCNA mRNA expression were also found in neurons throughout the central nervous system, however, no hybridization was observed in the white matter. Immunohistochemistry was also performed using 19F4 and PC10, and staining of progenitor cell nuclei in the subventricular zone was observed with both antibodies. Whereas 19F4 immunostaining was restricted to progenitor cells, PC10 immunostaining was also found in postmitotic nonproliferating cell nuclei. In the cortical neuroepithelium of developing mice, the distribution of PC10 immunoreactivity was wider than that of 19F4 immunoreactivity and PCNA mRNA expression. These results suggest that proliferating cell nuclear antigen mRNA is expressed not only in proliferating cells but also in nonproliferating cells such as neurons. The protein recognized only with PC10 may be a modified, most probably a phosphorylated PCNA.