D-type cyclins (cyclins D1, D2, and D3) are regarded as essential links between cell environment and the core cell cycle machinery. CyclinD1(CCND1), also known as BCL1. Expression of cyclin D1, but not of cyclins A and E, was induced by transfection of the RB gene into RB-deficient tumor cells. CCND1 gene to 11q13. cyclin D1 gene can function as an oncogene. Cyclin D1 expression is regulated by the retinoblastoma protein.