# ﻿Immunofluorescence microscopy was performed using the following antibodies: CENP-F (sheep, raised against CENP-F aa 1,363C1,640, 1:1,000; a gift from S

﻿Immunofluorescence microscopy was performed using the following antibodies: CENP-F (sheep, raised against CENP-F aa 1,363C1,640, 1:1,000; a gift from S. Plk4 levels in cells that lack centrioles led to the penetrant formation of de novo centrioles that gained the ability to organize microtubules and duplicate. In summary, we uncover a p53-dependent surveillance mechanism that protects against genome instability by preventing cell growth after centriole duplication failure. Introduction Centrosomes are the main microtubule-organizing centers (MTOCs) of most animal cells and are composed of a pair of centrioles surrounded by pericentriolar material (PCM; Nigg and Raff, 2009; G?nczy, 2012). Centrioles act as the centrosome organizer and thus their duplication controls centrosome number. Like DNA, centrioles duplicate exactly once per cell cycle, with a single new procentriole forming on the wall of each existing centriole (Tsou and Stearns, 2006). This tightly controlled process ensures the generation of two centrosomes to form the poles of the bipolar mitotic spindle. Errors in centriole duplication lead to abnormal centrosome number, which can result in chromosome segregation errors and the production of aneuploid progeny (Ganem et al., 2009; Silkworth et al., 2009). Aberrations in centrosome number have been associated with BBD several human diseases, including cancer and neurodevelopmental disorders (Nigg and Raff, 2009). Canonical centriole duplication begins at the G1/S transition with the assembly of a single cartwheel structure on the wall of BBD each preexisting mother centriole. The cartwheel then templates the formation of a procentriole by providing a scaffold onto which microtubules are loaded (Kitagawa et al., 2011; van Breugel et al., 2011, 2014). In addition to this canonical pathway of centriole assembly, de novo centriole formation can occur in the absence of existing centrioles (Miki-Noumura, 1977; Sz?llosi and Ozil, 1991; Palazzo et al., 1992; Marshall et al., 2001; Suh et al., 2002). A striking example of this process occurs in mouse embryos, where cell divisions continue in the absence of centrioles until the 64-cell stage, at which point centrioles are created de novo (Szollosi et al., 1972). In vertebrate somatic cells, a variable number of de novo centrioles are generated after experimental removal of existing centrioles (Khodjakov et al., 2002; La Terra et al., 2005; Uetake et al., 2007). It is therefore thought that BBD existing centrioles act to suppress de novo centriole assembly, although the molecular mechanism for this suppression remains unclear. Previous approaches to study the immediate consequence of centriole loss in human cells have RLC relied on laser ablation or microsurgery (Khodjakov et al., 2002; La Terra et al., 2005; Uetake et al., 2007). These elegant approaches only transiently remove centrioles from a small number of cells. Permanent centriole loss has been achieved through the knockout of essential centriole components (Sir et al., 2013; Bazzi and Anderson, 2014; Izquierdo et al., 2014). Although informative, these studies did not address the immediate effects of centriole duplication failure and were unable to temporally control formation of new centrioles. Polo-like kinase 4 (Plk4) has emerged as a conserved, dose-dependent regulator of centriole copy number and offers an attractive target to reversibly modulate centriole number in populations of cells (Bettencourt-Dias et al., 2005; Habedanck et al., 2005). Plk4 is a self-regulating enzyme that phosphorylates itself to promote its own destruction (Cunha-Ferreira et al., 2009, 2013; Rogers et al., 2009; Guderian et al., 2010; Holland et al., 2010; Brownlee et al., 2011; Klebba et al., 2013). This autoregulated destruction plays an important role in controlling the abundance of endogenous Plk4 and thereby helps to limit centriole duplication to once per cell cycle (Holland et al., 2012b). RNA interference and knock-in approaches have been used to inhibit Plk4 function, but these strategies are slow.