Evidence for inherent morphogenetic properties of the myogenic regions of the embryonic chick wing.

The dorsal and ventral myogenic regions were isolated from the right and left wings of donor chick embryos. After removal of the ectoderm, the myogenic regions were grafted into the dorsal myogenic region of the right wing of host embryos in normal or reversed proximal-distal orientation. All grafts were made so that the surface of the graft originally in contact with ectoderm was dorsal. It was expected that myogenic regions grafted into the myogenic region would participate in the normal formation of the host wing. However, after 7 days of further development many of the host wings had developed abnormal cartilages. To investigate the interactions between the tissue of the host and the tissue of the graft and the source of the tissue giving rise to ectopic cartilages, the donor embryos were labeled with tritiated thymidine. The location and shape of the graft were recorded at the time of the operation. The host wings and adjacent body wall were fixed 1, 3, and 4 days after the operation, sectioned, and prepared as autoradiographs. The location of the grafted cells in the host wing was determined by reconstructing the host wing and adjacent body wall. Serial sections and the reconstructions were examined to discover the correlates of abnormal cartilage formation. The following observations were made: 1) Grafts from the dorsal region of the right and left wing in normal orientation participated in the formation of the groove at the base of the wing ventral to the nineteenth somite that produces the extensor surface of the elbow. Grafts from the ventral region of the right and left wing in normal orientation, and all grafts in reversed orientation, did not participate in the formation of the groove. 2) Grafts in normal orientation increased in length on the axis of the humerus and did not increase in width. Grafts in reversed orientation increased in both length and width. Increase in width caused the graft to extend into the proximo-caudal corner of the wing. 3) Wings with grafts from the dorsal regions of the right and left wings in normal orientation were not clearly abnormal 4 days after the operation. When the groove ventral to the nineteenth somite did not form normally, ectopic cartilage differentiated where the groove should have been from grafted cells of the myogenic region. Increase in width of the graft into the proximo-caudal corner of the wing produced an increased mass of graft cells ventral to the nineteenth somite and an increased amount of ectopic cartilage.