The CTR is a microtubule-organizing center (MTOC) that usually lies between the leading edge and nucleus of cells showing directed migration (Rakic, 1972; Ueda et al., 1997). In migrating neurons, the CTR is located at the base of the leading neurite and anchors an array of microtubules (MTs)—the so-called perinuclear cage- that binds the nucleus and CTR and directs nuclear movements toward the CTR (Rivas and Hatten, 1995; Higginbotham and Gleeson, 2007). However, the nucleus can precede or transiently overtake the CTR in migrating neurons (Umeshima et al., 2007; Distel et al., 2010), showing that the control of cell directionality is an integrated and complex

process that moreover requires MT stability (Baudoin et al., 2008). An Selleckchem OSI744 MK1775 important function of the CTR, which has recently been re-emphasized, is the capacity to differentiate a primary cilium (Christensen et al., 2008; Louvi and Grove, 2011). The primary cilium is a small

protrusion at the cell surface assembled and maintained at the distal end of the mother centriole by the intraflagellar transport (IFT) machinery (Rosenbaum and Witman, 2002). The primary cilium functions as an antenna to probe and integrate extracellular signals, especially morphogens and growth factors, to control cell proliferation, cell differentiation, and cell migration (Breunig et al., 2008; Han et al., 2008; Spassky et al., 2008; Schneider et al., 2010). Primary cilia are present in interphasic neural stem cells in embryonic and adult brain as well as in adult differentiated neurons (Cohen et al., 1988; Fuchs and Schwark, 2004; Arellano et al., 2012). Mutations heptaminol of IFT proteins compromise primary cilium assembly and are associated with pleiotropic disorders including mental retardation and ataxia in humans (Lee and Gleeson, 2010). Although studies in animal models confirm that IFT plays important roles in brain neurogenesis and morphogenesis through impaired Shh signaling (Breunig et al., 2008; Han et al.,

2008; Spassky et al., 2008; Willaredt et al., 2008; Gorivodsky et al., 2009; Stottmann et al., 2009; Besse et al., 2011), the role of IFT in controlling neuronal migration is unknown. Whether immature neurons have a functional primary cilium is uncertain (Louvi and Grove, 2011; Arellano et al., 2012). We have examined this issue in neurons migrating tangentially from the medial ganglionic eminence (MGE) of the basal telencephalon to the cerebral cortex in which they differentiate as cortical GABAergic interneurons. MGE cells first migrate tangentially to the brain surface in the cortical primordium either in the marginal zone or deep in the intermediate zone. Then they colonize the cortical plate (CP) by reorienting their trajectories from tangential to radial or oblique (Tanaka et al.