Analysis of siRNAs disrupting the cell cycle In normal exponential growth, cells are transitioning from interphase to mitosis and back to interphase at con stant rates. We focused on four types of disruptions selleckchem Enzastaurin of the basal cell cycle shown in Figure 2, quiescence, when cells stop dividing, mitotic arrest, when cells stop going back in interphase, polynucleation, when cells start becoming polynucleated and cell death, when cells start to die. Each of these events was associated with a corresponding transition penetrance and inflection time. Transition penetrances proved to be reliable indicators of disruptions of the cell cycle. As an example, in cell death, cells growing in the control spots siCOPB1 had a significantly higher mean cell death penetrance than cells seeded in the negative control spots.

This is in agreement with the essential role of COPB1 in binding Golgi vesicles. Similarly, cells sub ject to siKIF11 had a significant higher mean mitotic arrest penetrance than negative control spots and a high mean cell death penetrance, consis tent with cell death that follows prometaphase arrest induced by the treatment. Based on these observations, we defined thresholds on each of the four transition pen etrances to detect the siRNAs that disrupt the cell cycle. Transition inflection points quantified the times of disruption of the cell cycle. For each siRNA, we sum marised the four times obtained from the replicate spots by average and standard deviation.

We identified genes with reproducible cell cycle disruption times by requiring standard deviation of less than 4 h and average of less than 50 h after seeding time, the latter criterion was motivated by the generally lower confidence of the inflection time estimates at later times. Using these criteria, we found 168 siRNAs leading to quiescence at reproducible times, 289 inducing mitotic arrest, 390 leading to polynucleation and 171 causing cell death Additional file 1, Table S1 The targets of the siRNAs inducing cell death included the protein units of the Golgi vesicular coat COPA and COPB2, several known apoptosis regulators such as TP53AIP1 and the RAS family members RAB25 and RAN. Interestingly, three siRNAs targeting COPA and COPB2 induced cell death at similar time points, together with siCOPB1. The similarity of these timings is consistent with the fact that the proteins are part of the same protein complex.

On the contrary, siRNAs directed at the RNA helicase DDX39A induced an early cell death at 22. 8 h, which could reflect a different cell death mechanism from the one caused by COPA and COPB2 inhibition. We also Batimastat identified several siRNAs inducing cell death and target ing uncharacterised genes such as C3orf26, C3orf52 or C16orf90. However, due to the existence of off target effects in RNA interference, functional res cue of the phenotypes and secondary functional assays would be needed to confirm the essential role of these genes.