Intrinsic cartilage-forming potential of dermomyotomal cells requires ectodermal signals for the development of the scapula blade

The avian scapula has a dual origin. The cranial part derives from the somatopleure of the forelimb field, while the caudal part, the scapula blade, originates from the dermomyotomes of the cervicothoracic transition zone. Thus, these dermomyotomes have, in addition to the well-known myogenic, angiogenic, and dermogenic potential, the ability to form cartilage. The scapula blade is therefore a derivative of dermomyotomal chondrogenesis. Although the mechanisms that direct the sclerotomal chondrogenesis are beginning to be understood, little is known about dermomyotomal chondrogenesis. Here, we address the mechanisms that control dermomyotomal cells to become chondrocytes. After heterotopic transplantation of dorsal epithelial somite halves from the scapula-forming level to the cervical level, the grafted tissue retains the capability to form cartilage, indicating that the dermomyotomal chondrogenic potential must be specified during anterior-to-posterior regionalisation of the paraxial mesoderm. Furthermore, we show that signals from the ectoderm are required, allowing dermomyotome cells to express markers associated with the chondrogenic lineage.