x1 = cyclin_D_Cdk4_6
x2 = transcription_factor_E2F_active
x3 = cyclin_E_Cdk2
x4 = cyclin_A_Cdk2
x5 = cyclin_B_Cdk1
x6 = Cdc20_active
x7 = E2F_total
x8 = Cdc20_total