DiI-labeled cranial neural crest cells were followed in whole embryo chick explant cultures using time-lapse confocal microscopy. Neural crest cells emerged along the dorsal midline of all rhombomeres. There was a small amount of mixing of neural crest cells between adjoining rhombomeres as cells emerged from the dorsal midline; this mixing persisted during their migration out of the neural tube. Neural crest cell-free zones lateral to rhombomere 3 (r3) and r5 resulted from neural crest cells migrating in either rostral or caudal directions to join other neural crest cells exiting adjacent to r2, r4, or r6. Neural crest cells migrated in a wide variety of individual cell behaviors, ranging from rapid unidirectional motion to stationary and even backward movement (toward the neural tube). Neural crest cells also migrated collectively, extending filipodia to form chain-like cell arrangements. In the midbrain and r1 region, many chains stretched from the dorsal midline to just beyond the lateral extent of the neural tube. In the r7 region, cells linked together and stretched laterally from the neural tube to other neural crest cells migrating into the third branchial arch. The unpredictable cell trajectories, the mixing of neural crest cells between adjoining rhombomeres, and the diversity in cell migration behavior within any particular region imply that no single mechanism guides migration. The regional differences in cell migration characteristics suggests that influential factors may vary spatially along the rostrocaudal axis in the head.
Copyright 1998 Academic Press.