Localized vascular regression during limb morphogenesis in the chicken embryo. I. Spatial and temporal changes in the vascular pattern.

Morphogenesis of the vertebrate limb bud depends upon reciprocal interactions between epithelial and mesenchymal tissues. A characteristic limb vascular pattern is essential for normal limb outgrowth. The vascular pattern in the distal portion of the wing bud was examined by ink injection and compared to the sites of cartilage differentiation, as indicated by [35S]-incorporation. During development, avascular areas arose in three distinct locations within the vascularized mesoderm. These areas corresponded to the distal skeletal elements, referred to as digits 2, 3, and 4. Incorporation of radioactive sulfate was high in the avascular areas and low in the adjacent vascular tissue. Examination of autoradiographs of ink-injected limbs suggested that the appearance of avascular regions preceded the accumulation of sulfated cartilage matrix. These results indicate that remodeling of the limb vasculature is related to the formation of the skeletal pattern.