Fig. 5. Physically induced turning of interneurons requires leading process branching. (A) Schematic diagram of experimental design. After dissection of an E13.5 GFP MGE into small pieces, microtransplants were placed on a host E13.5 wild-type MGE and 5 hours later the pallium was removed from slices by cutting at the pallial-subpallial boundary. After 12 hours of incubation, GFP interneurons have migrated just a short distance from the cut (B). At this time, vehicle or Y27632 (30 µM) was added to the medium and slices were incubated for another 12 hours. (C-D') Images of GFP-expressing interneurons migrating in slices in the presence of vehicle (C,C') or Y27632 (D,D'). (C',D') High-magnification images of the boxed areas shown in C,D, respectively. Note that interneurons reach the cut in a fairly delineated stream in both control and experimental slices (arrows in C,D). In control slices, many interneurons turn 90° to continue migrating parallel to the incision (C), while turning is diminished in the presence of Y27632 (D). (E) Light-gray, dark-gray and pink arrowheads indicate type 1 (leading process parallel to the cut), type 2 (leading process away from the cut) and type 3 (leading process towards the cut) cells, respectively. (F) Quantification of the relative proportion of type 1-3 cells in control and experimental slices. Histograms show averages ±s.e.m. Control: 56.56±1.79%, 18.68±1.86%, 24.76±2.09% for cell type 1, 2 and 3 respectively; 1151 cells from eight slices in three independent experiments. Y27632: 42.80±1.85%, 18.17±1.98%, 39.03±2.36% for cell type 1, 2 and 3 respectively; 743 cells from eight slices in three independent experiments. ²-test: ^***P<0.001. Scale bars: 100 µm in B,C,D; 25 µm in C',D'.