In the past few years, however, work in other vertebrate and nonvertebrate chordate systems has come to play an important role in the field and has shed light on generalities and differences among chordates. The nature of the neural inducer or inducers and the mechanism of neural induction have been and remain hot topics in developmental biology.įor half a century after Spemann and Mangold, studies on amphibians monopolized the subject, and even more recently, a large part of the progress in analyzing organizer formation and function and neural induction was based on amphibians, mostly the model species Xenopus laevis. And neural induction has for a long time been regarded as a process by which organizer signals, in their normal context, redirect ectodermal cells from an epidermal towards a neural fate. which-as the transplantation experiment shows-is able to turn cells whose original fate would be gut or ventral epidermis into brain or somites, is the prototypical inducing tissue. The signal-receiving cells must be capable of responding, a property termed competence. Induction refers to the change in fate of a group of cells in response to signals from other cells. Most of the axis, including the nervous system, was derived from the host, whose cells were induced to form an axis by the graft, therefore named the organizer. In what is usually referred to as the most famous experiment in embryology, Hans Spemann and Hilde Mangold (1924) showed that a specific region in early frog embryos called the blastopore lip can induce a second complete embryonic axis, including the head, when transplanted to a host embryo.
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