Development of grafts from mouse embryos to the wing bud of the chick embryo

Abstract

The apical zone of embryonic mouse limb buds when transplanted to the dorsal surface of 3-day chick wing buds develops into well-formed toes. These are about the size of normal mouse toes of the same chronological age and are small in proportion to 10–15 day chick host wings. Chick cartilage and connective tissue are included in the proximal part of the toes. Mesoderm from young mouse limb buds (equivalent to chick wing buds of stages 18–24) when inserted between the ectodermal ridge and apical mesoderm of chick wing buds remains in the apex of the outgrowing bud, grows rapidly, and differentiates into cartilages and other connective tissues associated with the digital structures of the host manus. The location, size, and number of elements, and occasional toelike outgrowths, indicate that the mouse implants differentiate as toes. Mesoderm from older mouse limbs or from the maxillary process when similarly implanted in the chick wing bud interferes with distal elongation of the host bud. Mitotic activity occurs in the implant, but the amount of growth is markedly less than that observed when limb bud mesoderm is implanted. These observations demonstrate that grafts from mouse embryos to the chick wing bud develop in the same manner as corresponding grafts from various regions of chick embryos, and exhibit the same sharp distinction between the behavior of limb bud mesoderm and other mesoderm. Mouse limb bud development thus requires the same interaction between the ectodermal apical ridge and the limb bud mesoderm that occurs in the chick. The increased size which results from growth in the implanted mouse mesoderm can be observed directly during the limb bud stages. The finding that a large increase occurs without intermingling of chick cells with the mouse cells demonstrates that migration from proximal levels is not a necessary factor in distal elongation.