Cell death in cranial neural crest development.

The rhombencephalic neural crest, crucial to the patterning and development of many craniofacial structures, migrates laterally from the dorsal hindbrain, but not as a continuous sheet. We have used a vital dye to demonstrate a discontinuous pattern of cell death in the dorsal midline of the avian rhombencephalon associated with the migration of the neural crest. Whilst cell death commences in the dorsal midline of the presumptive mesencephalon at stage 8, two distinct domains of cell death are apparent in the rhombencephalon by stage 11. The rostral domain lies over primary rhombomere RhA1 and rhombomere rh3, while the caudal domain occurs on the neural midline between the otic vesicles, in the region of rh5. Using a marker for the neural crest, we show that the rostral and caudal domains of cell death correlate with the absence of neural crest migration from rh3 and rh5. Thus segment-specific cell death in the dorsal region of particular rhombomeres may account for their subsequent failure to contribute to the cranial neural crest.