Hans Spemann and Hilde Mangold: Primary Embryonic Induction
The most spectacular transplantation experiments were published by Hans Spemann and Hilde Mangold in 1924.* They showed that, of all the tissues in the early gastrula, only one has its fate determined. This self-differentiating tissue is the dorsal lip of the blastopore, the tissue derived from the gray crescent cytoplasm. When this dorsal lip tissue was transplanted into the presumptive belly skin region of another gastrula, it not only continued to be blastopore lip, but also initiated gastrulation and embryogenesis in the surrounding tissue (Figure 10.20). Two conjoined embryos were formed instead of one! In these experiments, Spemann and Mangold used differently pigmented embryos from two newt species: the darkly pigmented Triturus taeniatus and the nonpigmented Triturus cristatus. So when Spemann and Mangold prepared these transplants, they were able to readily identify host and donor tissues on the basis of color.† When the dorsal lip of an early T. taeniatus gastrula was removed and implanted into the region of an early T. cristatus gastrula fated to become ventral epidermis (belly skin), the dorsal lip tissue invaginated just as it would normally have done (showing self-determination), and disappeared beneath the vegetal cells. The pigmented donor tissue then continued to self-differentiate into the chordamesoderm (notochord) and other mesodermal structures that normally form from the dorsal lip. As the new donor-derived mesodermal cells moved forward, host cells began to participate in the production of the new embryo, becoming organs that normally they never would have formed. In this secondary embryo, a somite could be seen containing both pigmented (donor) and unpigmented (host) tissue. Even more spectacularly, the dorsal lip cells were able to interact with the host tissues to form a complete neural plate from host ectoderm. Eventually, a secondary embryo formed, face to face with its host....
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