The primary cilium of MGE cells likely assembles in a Golgi-derived vesicular compartment associated with the mother centriole by the intermediate of MTs. This Golgi-derived vesicle should fuse to the plasma membrane ( Sorokin, 1962; Cohen et al., 1988) to position the primary cilium at the cell surface. The CTR nucleates and anchors MTs (Bornens, 2012). The number of centrosomal MTs anchored to the centrioles

was significantly higher when the mother centriole was attached to the plasma membrane rather than positioned within the perinuclear cytoplasm (17.7 ± 1.5 anchored MTs against 5.5 ± 1.1, p < 0.001, n = 15 cells; compare Figures 1H and 1I and Figure 2B). In similar cocultures prepared for immunostaining, the MT minus-end protein ninein (Baird et al., 2004; Bellion et al., 2005) was detected at the CTR in only a fraction of migrating MGE cells (39%; Figure S2A), attesting that the AG-014699 mouse number of MTs attached to the CTR varied during the migration cycle. A large proportion of MTs reconstructed in the centrosomal region passed alongside the two centrioles without interruption in their vicinity (Figures 2A–2F; 80% ± 7.6% of the 87 MTs reconstructed at the rear of the centriole pair in 5 cells; see Movie S3). Thus, a number of MTs does not attach to any centriole in MGE cells, in agreement with γ-tubulin immunostaining

that identified the nuclear rear and the rostral swelling as extra-centrosomal sites of MT nucleation (Figure S2B). Since MTs anchored on the centrioles Mephenoxalone were oriented in majority to the leading edge (Figure 2G), nuclear translocations 17-AAG likely proceed by forward movements along MT bundles comprising extracentrosomal MTs, which extend between the perinuclear compartment and the rostral cytoplasmic swelling (Figures S2C–S2E). Our ultrastructural observations in combination with immunostaining experiments support the hypothesis

that ciliogenesis, CTR subcellular positioning, and centrosomal MT network organization are tightly linked and dynamically regulated during the migration cycle of MGE cells (summarized in Figure 2H). The number of MTs anchored to the centrioles should increase when the mother centriole is docked to the plasma membrane but should decrease as the mother centriole re-positions in the perinuclear cytoplasm. The morphology of the GA is moreover influenced by the MT organization in the centrosomal region since most ninein immunopositive MGE cells presented an elongated GA (Figure S2A). We thus examined whether signals transmitted through the primary cilium could influence the MT organization, the GA conformation, and the migratory behavior of MGE cells. MGE cells are generated in the basal forebrain under the control of Shh (Xu et al., 2005) and later migrate in the marginal and intermediate zones of the cortex that expresses Shh at low level (Komada et al., 2008).