|Budget Amount *help
¥2,500,000 (Direct Cost : ¥2,500,000)
Fiscal Year 1997 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 1996 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Cyclin-dependent kinase 5 (CDK5) is one of the cyclin-dependent kinases, and is expressed in mature neurons. CDK5 has been postulated to be a neurofilament or tau protein kinase, because it phosphorylates neurofilaments and tau protein in vitro. It has been reported that CDK5 was immunohistochemically detected only in axons of neurons. We here report the immunohistochemical study of CDK5 using two distinct antibodies, one recognizing the N-terminal of CDK5 and the other the C-terminal. Immunoreactivity of CDK5 was found not only in axons, but also intensively in nuclei, though not in nucleoli, of neurons in the mouse central and peripheral nervous systems. The nuclear CDK5 possibly has a physiological function distinct from the neurofilament or tau protein kinase.
Proliferating cell nuclear antigen (PCNA), the DNA polymerase auxiliary factor, is required for DNA replication and repair ; thus, PCNA is abundantly expressed in proliferating cells. Interestingly, PCNA mRNA was also detected in adult mouse brain by northern blot analysis. Two monoclonal antibodies against PCNA were used for western blot analysis, and one of them (clone PC10) detected a band in mouse brain extract, but the other (clone 19F4) did not. Immunohisto-chemistry of PCNA was also performed using these antibodies, and immunostaining was found only with PC10 in nuclei of cells, neurons and glia, over a wide area of the adult mouse central and peripheral nervous systems. On the other hand, nuclei of cells in the subventricular zone (SVZ) were stained with both PC10 and 19F4. These data suggest that the PCNA-like protein in mouse brain except for the SVZ is not PCNA but a structurally related PCNA analogue. However, the possibility also exists that the wide-spread PC10-immunoreactivity is due to the modification of amino acid residues of PCNA,such as by the phosphorylation.