A segmented pattern of cell death during development of the chick embryo.

During the early development of the chick embryo, specific groups of cells die in characteristic patterns. In this study, Nile Blue sulphate staining was used to reveal a novel pattern of segmentally repeated cell death in the paraxial mesoderm of the chick prior to stage 23. This pattern varies according to the developmental stage of the embryo and shifts rostrocaudally, corresponding to progressing somite differentiation. Initially, during early somite differentiation, cell death is restricted to the rostral half of the somite (the rostral pattern of cell death). After the somite has differentiated into dermomyotome and sclerotome, dead cells appear in superficial tissues in a pyramidal pattern which lies in register (rostrocaudally) with the central part of the sclerotome. Finally, small bands of dying cells are seen between the neural tube and the expanding sclerotome. This third pattern (the ventral path) lies in register with the rostral part of the caudal half of the sclerotome. We show by fluorescent labelling of the migrating neural crest that these patterns of cell death correspond to the routes of neural crest migration. In addition, serial sectioning of stage 23 chick embryos confirms that the position of dying cells correlates with the known routes of neural crest migration and with the sites of development of certain neural crest-derived tissues.