The relationship between limb muscle and endothelial cells migrating from single somite

Somites contribute myogenic and endothelial precursor cells to the limb bud. Transplantations of single somites have shown the pattern of muscle cell distribution from individual somites to individual limb muscles. However, the pattern of the endothelial cell distribution from individual somites to the limb has not been characterized. We have mapped quail muscle and endothelial cell distribution in the distal part of the chick limb after single somite transplantation to determine if there is a spatial relationship between muscle and endothelial cells originating from the same somite. Single brachial somites from quail donor embryos were transplanted into chick embryos, and, following incubation, serial sections were stained with a quail-endothelial cell-specific monoclonal antibody (QH-1), an anti-quail antibody (QCPN) and an anti-desmin antibody to distinguish the quail endothelial and muscle cells from chick cells. Our results show that transplants of somite 16-21 each gave rise to quail endothelial cells in the wing. The anterioposterior position of the blood vessels formed by somitic endothelial cells corresponded to the craniocaudal position of the somite from which they have originated. Endothelial cells were located not only in the peri- and endomysium but also in the subcutaneous, intermuscular, perineural and periost tissues. There was no strict correlation between the distribution of muscle and endothelial cell from a single transplanted somite. Blood vessels formed by grafted quail endothelial cells could invade the muscle that did not contain any quail muscle cells, and conversely a muscle composed of numerous quail muscle cells was lacking any endothelial cells of quail origin. Furthermore, a chimeric limb with very little quail muscle cells was found to contain numerous quail endothelial cells and vice versa. These results suggest that muscle and endothelial cells derived from the same somite migrate on different routes in the developing limb bud.