Cyclin D1 Transgenic Mouse Models

G1 cyclins influence whether initiation of a new cell cycle occurs. Expression of these cyclins is cell-cycle-phase dependent and regulated transcriptionally, post-transcriptionally and post-translationally (1–4). In addition, distinct human cyclin-dependent kinases—cdks—have been identified that associate with cyclins and share extensive amino-acid sequence identity with p34cdc2 (cdk). Thus, each cyclin is believed to regulate the cell cycle at its designated time-point by binding to and activating the cdks (1–4).