Regeneration following somite removal in chick embryos.

A technique was developed for ensuring complete removal of single somites with minimal damage to surrounding tissues in 2-day-old chick embryos. Histological examination of the site of somite removal at various time intervals after operation revealed that a regeneration mechanism could be triggered. Replacement of the cells that had been removed could occur, but the extent of the replacement was dependent on the immediate fate of the gap created. If the gap was closed by enlargement of the adjacent somites, no replacement of the cells occurred. If the gap remained, then cells invaded the gap and were able to produce a normal sclerotome and dermomyotome. By labelling adjacent cells with the carbocyanine dye. DiI, it was shown that the replacement cells could come from the adjacent somites, as well as the intermediate mesoderm. Use of an antibody to HNK-1 established that the replacement cells did not come from the neural crest and that the neural crest cell distribution was little affected. Staining with peanut agglutinin showed that the replacement cells were able to adopt the characteristics associated with rostral and caudal halves of the normal sclerotome. These results provide possible explanations for the variety of vertebral anomalies produced by removal of somites and for the production of some congenital vertebral anomalies.