Effects of excising the apical ectodermal ridge on the development of the marginal vasculature of the wing bud in the chick embryo

Publisher Website
Google Scholar
Abstract
The limb bud of the chick embryo depends for its outgrowth on an interaction between the apical ectodermal ridge (AER), which rims the apex of the bud, and the subjacent limb bud mesoderm. This report describes the results of experiments that were designed to test whether a relationship exists between the AER and the origin of the distinctive marginal veins, which drain the early arterial supply and capillary bed of the wing bud. All of the AER or localized portions of it were excised from wing buds of embryos at stages 17–23. Effects of the operation on the vascular pattern were analyzed in specimens whose blood vessels were injected with India ink at appropriate postoperative intervals. Excision of all or part of the AER at stages prior to the formation of the marginal vein results in complete or partial failure of the marginal veins to form, depending on the extent of ridge deletion. Once the marginal vein is formed proximally, however, it persists proximally even after the AER is removed, but distally it fails to form. Limb bud mesoderm, encased in backskin ectoderm and grafted to a host embryo, fails to form a marginal vein, indicating that nonridge ectoderm will not substitute for the AER in promoting normal vascularization. Isolated limb buds grafted to the chorioallantoic membrane with their normal ectodermal covering show normal vasculogenesis, indicating that the vascular pattern of the limb is intrinsically determined. These results indicate that the AER is required for the establishment of the marginal veins and the formation of a characteristic vascular pattern in the limb.