Morphology and orientation of GFP cells in the MZ in fixed cortices. A–F, GFP cell morphology in the MZ in E12Ge:E15.5 (A, B, D, E), E11.5Ge:E17.5 (C), or E12Ge:E17.5 (F) cortices. A, GFP cells are oriented in many directions. B, A cell with distinct leading process reminiscent of a directed cell. C, This cell also has a distinct leading process, but its trailing process is curved (arrowheads), a morphology similar to that of wandering cells in the course of turning (Fig. 1C, frame 10:00). D–F, These cells show a multipolar morphology similar to stationary cells (compare D–F, Fig. 1B, frames 28:00 and 4:00, respectively). G, The proportion of GFP cells with a different number of primary processes in fixed E12Ge:E15.5 cortices (n = 175 cells, 6 brains) (average ± SEM). Digits with large letters, 0–5, indicate the number of processes. Whereas a majority (∼60%) of GFP cells extended one or two processes, one-third of them extended more than three processes. Note that the proportion of cells with one or two processes is comparable with that of the sum of directed and wandering cells (Fig. 2C) and that of the cells with more than two processes is comparable with that of stationary cells. H, Quantification of the orientation of leading processes of GFP cells in fixed E12Ge:E15.5 cortices (gray region; n = 115 cells, 6 brains). A similar polar plot of GFP cells migrating in E12Ge:E15.5 cortices in vitro was superimposed for comparison (dashed line; n = 181 cells, 8 brains). Note the similarity between the two results. The leading processes of GFP cells that extend one or two processes were subjected to the analysis. The leading process was defined as the thickest process extending from a GFP cell. The orientation of leading processes was defined as that of a line connecting the cell body center and the base of the leading process. Medial (M) was defined as 0°, and rostral (R) was defined as 90°. The horizontal plane was then subdivided into 12 sectors, and the proportion of cells with an orientation that falls into each sector was plotted as a polar diagram. For the analysis of the direction of migrating cells in vitro, their preferred migrating cells was defined as those migrating at rate of >5 μm/h. For the analysis of directionality, the horizontal plane was subdivided into 12 sectors, and the proportion of cells with a preferred direction that falls into each sector was scored. The preferred direction of migrating GFP cells (see Materials and Methods) was plotted in the same way as above. L, Lateral.; C, caudal. Scale bars: A, 40 μm; B–F, 10 μm.