Fig. 2. Time-course and rhombomeric origin of aberrantly migrating NCCs. Before left-side r3 removal, cells in r4 or r2 were marked in one of two ways. In some embryos, cells within dorsal r4 or r2 were labelled by focal DiI injection. These embryos were allowed to develop for a further 5, 10, 20 or 30 hours and processed for Sox10 in situ hybridisation. In other embryos, r4 or r2 were replaced homotopically with quail rhombomeres. These embryos were allowed to develop for a further 72 hours and processed for anti-Q¢PN immunohistochemistry. (A-C) Dorsal views 5 hours after r3 removal. r4 cells have migrated appropriately towards ba2, while very few cells migrate aberrantly into mesenchyme adjacent to the removed r3 (r3*) (arrow) or directly into the space left by removing r3 (arrowhead). Appropriately migrating r4 cells express Sox10 (a marker of migrating NCCs), but Sox10 expression is not detected in aberrantly migrating r4 cells. (D-F) Dorsal views 10 hours after r3 removal. Several r4 cells have now migrated aberrantly into r3* mesenchyme (arrow) and Sox10 is expressed within proximal r3* mesenchyme. However, some aberrantly migrating r4 cells, more distal to the neuroepithelium, do not express Sox10 (arrowhead). (G-I) Dorsal views 20 hours after r3 removal. A robust stream of aberrantly migrating r4 cells is present within r3* mesenchyme (arrow) and intersects the stream of neural crest cells from r2. All of the aberrantly migrating r4 cells within r3* mesenchyme now fall within the region of Sox10 expression. (J-L) Lateral views of operated side 30 hours after r3 removal. Aberrantly migrating r4 cells are within r3* mesenchyme and can be detected within the developing trigeminal ganglion (arrowheads). (M-O) Dorsal views 20 hours after r3 removal. Many r2 cells are migrating appropriately towards ba1, but DiI labelled r2 cells seldom migrate aberrantly into r3* mesenchyme (arrow), even though a robust stream of Sox10 expressing, aberrantly migrating cells was detected within r3* mesenchyme in these embryos (arrowhead). (P-R) Dorsal views. By 30 hours after r3 removal, r2 cells had migrated into r3* mesenchyme (arrow) and were occasionally seen within the developing facial/acoustic ganglion (arrowhead). (S-X) Sagittal sections of quail-to-chick homotopic r2 or r4 grafts, stained with Q¢PN antibody 72 hours after r3 removal. (S) r2-derived quail cells were located appropriately within the trigeminal ganglion (gV) and ectopically within the facial ganglion (gVII) and the ectopic cranial nerve (arrow). (T-U) Quail r2 cells were not found within ba2 on either the operated (T) or control (U) sides. (V) Quail r4-derived cells were located appropriately within the facial ganglion and ectopically within the trigeminal ganglion and the ectopic cranial nerve (arrow). (W) Quail r4 cells were found ectopically within ba1 (arrow), but were not seen in ba1 on the unoperated side (X). ba1, branchial arch 1; ba2, branchial arch 2.
