Any part of an embryo capable of inducing another part to differentiate. Frequently mentioned examples of an organizer are the dorsal lip of the blastopore and Hensen’s node. It was Hans Spemann ((1869-1941) who identified the dorsal lip as the organizer, together with his graduate student Hilde Mangold (1898-1924), for which he received the Nobel Prize for Physiology or Medicine in 1935. Since then, it has been known as Spemann’s organizer. For more than fifty years following Spemann, there was confusion about what property or product of the dorsal lip tissue was responsible for in its role as an organizer. With the discovery of much earlier events that established the embryonic axes in the 1980s, insights began to be gained about where and how the blastopore and the organizer will form.
See Archenteron, Blastopore, Competence (embryology), Differentiation (embryology), Equipotentiality, Experimental embryology, Hensen’s node, Hox genes, Induction (embryology), Morphogenetic field, Noggin