Early Embryonic Induction: The Ectodermal Target Cells

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Abstract

Spemann’s and Hilde Mangold’s famous transplantation experiment[1] showed that in amphibians competent ectoderm (presumptive epidermis) could be triggered to differentiate into neural tissues by the upper blastopore lip of early amphibian gastrulae. Spemann entitled this area with inducing activity as the organisator (organizer), because it organizes the formation of the central nervous system. In the following decades the interest of embryologists has been focused on the question, which factors located in the upper blastopore lip are responsible for the process of primary embryonic induction. Morphogenetic factors, which induce in competent ectoderm the formation of endodermal, mesodermal and neural derivatives, could be isolated from different sources[2–13]. A vegetalizing factor could be isolated in highly purified form from chicken embryos[14,15]. It is now generally accepted that these factors, which in contrast to growth factors can be entitled as determination factors, are protein in nature.