Origin of myotome cells in the chick embryo studied by 3H-thymidine autoradiography and acetylcholinesterase histochemistry

3H-thymidine autoradiography and acetylcholinesterase (AChE) histochemistry were performed on the same plastic sections to examine the origin of myotome cells in the chick embryo.The myotome first forms in the dorso-medial angle of the dermomyotome and elongates ventro-laterally along the inner surface of the dermomyotome with development. The myotome consists of numerous AChE-positive cells and some AChE-negative cells.Two hr after injection of 3H-thymidine, a few AChE-negative cells but none of the AChE-positive myotome cells were labeled. Four hr after the injection, a few labeled AChE-positive and AChE-negative cells were observed throughout the myotome and thereafter, the labeling of the AChE-positive as well as AChE-negative cells increased with time. Twenty-four hr after the treatment, many labeled cells were distributed throughout the myotome, but unlabeled ACNE-positive cells were also evident in the myotome.In the present study, the proliferating ability and origin of myotome cells in the chick embryo are discussed.