Our data show that barr2 shares many of the hallmarks of proteins found at the primary cilium or involved in ciliogenesis: it is targeted to the centrosome in cycling cells and to the basal body and axoneme of PC in 
quiescent cells; its depletion results in accelerated and uncontrolled cell Cinoxacin growth resulting in impaired ciliogenesis. Similar to many PC proteins, such as, Polaris/IFT88, IFT20 or IFT57, barr2 was found at the centrosome in cycling cells and more precisely at the proximal part of the centrioles. Although we could not find evidence for a role of barr2 in the basic functions of the centrosome, barr2 shares with other centrosome-associated proteins a role in cell cycle regulation. The centrosome participates in several different cell cycle regulatory events, such as G1/S transition, cytokinesis, and monitoring of DNA damage, functions which involve the recruitment of specific sets of proteins. Recent studies showed that depletion of structural centrosomal proteins, such as PCM-1 or pericentrin results in a p53-dependent G1/S arrest, suggesting that the centrosome itself is involved in cell cycle control. Consistent with these observations, we found that barrs-deficient cells do not respond properly to serum starvation, as shown by their persistent growth in low serum and their failure to enter in G0 phase, whereas they proliferate faster in high serum conditions. The strong additive effect of the simultaneous depletion of both barrs likely reflects the fact that each isoform may have specific points of impact. A role ofbarr1 was reported in G1/S transition downstream of IGF receptor, and via a receptor-independent enhancement of p27 transcription, which, in turn, inhibits G1/S transition. Consistent with our observations on 1KO MEFs, depletion of barr1 in the latter study was shown to increase cell proliferation. barr2 was also reported to control cell growth in response to nerve growth factor in PC12 cells. However, the mechanism by whichbarr2 controlscellcycle appears to be different. barr2 interacts with mdm2, the E3 ubiquitin ligase controlling the stability of p53, a transcriptional factor which plays a major role in cell cycle regulation. barr2 was specifically reported to Atropine sulfate actively exclude mdm2 from the nucleus, to stabilize p53 by this mechanism, leading to either induction of apoptosis or cell cycle arrest at G2/M transition.