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Primary cilia are crucial for several signal transduction pathways (Goetz and Anderson, 2010). Their assembly is an ordered process that must be closely integrated with the cell cycle because of the dual roles of centrioles in ciliation and in mitosis (Sorokin, 1962; Seeley and Nachury, 2010; Ishikawa and Marshall, 2011). After cell division, a daughter cell inherits a centrosome that consists of pericentriolar material (PCM) in which are embedded two centrioles, barrel-shaped structures of triplet microtubules arranged with a ninefold symmetry. The centrioles differ from one another: the older of the two carries distal and subdistal appendages and is termed the mother centriole, as distinct from the younger, daughter centriole. During centrosome duplication in S phase, both centrioles will serve as the foundation for new procentrioles, although the daughter only acquires its appendages later in the cycle (Nigg and Stearns, 2011). These appendages are key to the plasma membrane recruitment of the mother centriole to serve as a basal body, the structure from which the ciliary axoneme extends in a membranebounded, nine-membered array of doublet microtubules. Primary cilia are found in most cell types in the body but have not been described in lymphocytes. Although the reasons for a general lack of ciliation in lymphocytes are unclear, it is possible that this is related to the requirement of centrosomes for immune cell function. The movement of centrosomes toward the immune synapse, a membrane region at which cells of the immune system contact their target cells, helps to establish a specialized structure that has several similarities with cilia (Stinchcombe and Griffiths, 2014). Although no axoneme is formed at the immune synapse, several ciliary components have been implicated in immune synapse functions (Finetti et al., 2009), so that certain immune cell functions may not be compatible with the capacity for primary ciliogenesis (Griffiths et al., 2010). However, whether lymphocytes are capable of making cilia is an open question. The mechanism that controls the functional change from centriole to basal body is not fully understood (Kobayashi and Dynlacht, 2011). A complex that includes CP110 and Cep97 acts as a cap at the distal end of centrioles to block mother centriole conversion to a basal body (Kleylein-Sohn et al., 2007; Spektor et al., 2007; Tsang et al., 2008). CP110 levels are regulated during the cell cycle by targeted degradation through the ubiquitin– proteasome system (D’Angiolella et al., 2010; Li et al., 2013), with TTBK2 (tau tubulin kinase 2) also being required for efficient removal of CP110 (Goetz et al., 2012; Čajánek and Nigg, 2014). Another interactor of CP110 is centrin2, a small, highly conserved calcium-binding protein, although the functional significance of this interaction in cilium regulation is unknown Primary cilia are antenna-like sensory microtubule structures that extend from basal bodies, plasma membrane–docked mother centrioles. Cellular quiescence potentiates ciliogenesis, but the regulation of basal body formation is not fully understood. We used reverse genetics to test the role of the small calcium-binding protein, centrin2, in ciliogenesis. Primary cilia arise in most cell types but have not been described in lymphocytes. We show here that serum starvation of transformed, cultured B and T cells caused primary ciliogenesis. Efficient ciliogenesis in chicken DT40 B lymphocytes required centrin2. We disrupted CETN2 in human retinal pigmented epithelial cells, and despite having intact centrioles, they were unable to make cilia upon serum starvation, showing abnormal localization of distal appendage proteins and failing to remove the ciliation inhibitor CP110. Knockdown of CP110 rescued ciliation in CETN2-deficient cells. Thus, centrin2 regulates primary ciliogenesis through controlling CP110 levels. Centrin2 regulates CP110 removal in primary cilium formation