Differential changes of cell cycle regulators and activities in kidneys during pre- and postnatal development

The present study was designed to determine the changes of the cyclin/CDK (cyclin dependent kinase)/CKI (CDK inhibitors) system in kidneys during pre- and postnatal development. All protein levels of cyclins (cyclins D1, D3, E, A, B) and protein levels and activities of CDKs (CDK4, CDK2, cdc2) were high in kidneys during the prenatal period and decreased differently during the postnatal period. As the phosphorylated active form of cyclin D1 decreased, the dephosphorylated inactive form of cyclin D1 increased during the early postnatal development. While CDK4 activities decreased markedly, the activities of CDK2 and cdc2 decreased gradually during the early postnatal period. While the p21(CIP1) protein was barely detectable during the prenatal period, but was not detectable during the postnatal period, the protein level of p27(KIP1) was detectable during pre- and postnatal periods. These results indicate that the cyclin/CDK/CKI system is actively involved in the nephrogenesis during the prenatal period and is closely associated with the withdrawal of the renal cell cycle during the postnatal period.