Three different fates of cells migrating from somites into the limb bud.

Cells from the ventrolateral dermomyotomal lips at limb levels undergo epithelio-mesenchymal transition and migrate as individual and undifferentiated cells into the limb buds. The cells give rise to myocytes and blood vascular endothelial cells (BECs) in the limb. Using vascular endothelial growth factor receptor-3 (VEGFR-3) as a marker, it has also been shown that the somites contribute to endothelial cells of lymphatic vessels in the limbs, but it is unknown where the lymphangiogenic precursors are located within the somite. In this study we used the transcription factor Prox1 as a lymphatic marker and investigated whether cells in the dorso-lateral quarter of the somite differentiate into lymphatic endothelial cells (LECs) of the limbs. To label the migrating cells, the dorso-lateral part of an epithelial brachial somite was grafted homotopically from quail into chick embryos at HH stages 13-14. The chick hosts were incubated until day 10-11 of development. The quail cell nuclei were identified with QCPN (anti-quail) antibodies. Cell differentiation was analysed by immunohistochemical staining with QH1, anti-desmin and anti-Prox1 antibodies, and by in situ hybridisation with Prox1 probes. Our results confirm that quail cell nuclei are incorporated into the myotubes of the limb muscles. Quail cells are found in the endothelium of limb blood vessels and lymphatics, predominantly the dermal lymphatics. This indicates that superficial lymphatics develop independently from the deep ones and shows that cells migrating from the lateral somitic edge into the limb buds differentiate into three cell populations: myocytes, BECs and LECs.