The Spemann-Mangold organizer, also known as the Spemann organizer, is a cluster of cells in the developing embryo of an amphibian that induces development of the central nervous system. Hilde Mangold was a PhD candidate who conducted the organizer experiment in 1921 under the direction of her graduate advisor, Hans Spemann, at the University of Freiburg in Freiburg, German. The discovery of the Spemann-Mangold organizer introduced the concept of induction in embryonic development. Now integral to the field of developmental biology, induction is the process by which the identity of certain cells influences the developmental fate of surrounding cells. Spemann received the Nobel Prize in Medicine in 1935 for his work in describing the process of induction in amphibians. The Spemann-Mangold organizer drew the attention of embryologists, and it spurred numerous experiments on the nature of induction in many types of developing embryos.
Between February 1969 and August 1970 Edward Kollar and Grace Baird, from the University of Chicago in Chicago, Illinois, published three papers that established the role of the mesenchyme in tooth induction. Drawing upon a history of using tissue interactions to understand differentiation, Kollar and Baird designed their experiments to understand how differentiated structures become specified. Their work overturned a widely accepted model that epithelium controls the identity of the structure, a phenomenon called structural specificity. Interactions between epithelium and mesenchyme control the development and differentiation of many parts during embryonic development, including structures like the gastrointestinal tract and hair. Thus, the realization that mesenchyme drives induction and differentiation during epithelio-mesenchymal interactions had far-reaching effects.
Joseph Needham was an embryologist and biochemist who is most noted in science for his studies on induction in developing embryos. Needham worked with Conrad Hal Waddington to attempt to identify the compound responsible for the organizer's activity. Although he was not successful in discovering the chemical, he and Waddington learned much about the organizer. Needham was a meticulous writer, writing reviews and books about contemporary research. In later years, Needham traveled to a newly opened China and studied their history, writing a number of books on Chinese culture, science, and history. Born Noel Joseph Terrence Montgomery Needham on 9 December 1900 in London, his parents were Alicia Adelade Montgomery and Joseph Needham. His parents' relationship ended poorly while he was a child and he was often forced to mediate between them, a skill he utilized in later years. He pursued science and philosophy, subjects that also interested his father.
Research in chemical induction seeks to identify the compound or compounds responsible for differentiation in a developing embryo. Soren Lovtrup compared the search for these compounds to the search for the philosopher's stone. It was based on the assumption that the differentiating agents have to be chemical substances either within cells or in the extracellular matrix. However, despite numerous efforts to understand them, the nature of these substances remained largely a mystery from the 1930s until the 1980s, when the new era of molecular induction based on molecular genetics provided a new perspective. During the period of emphasis on chemical induction, a variety of different experiments were conducted aimed at discovering the chemical nature of the inducer. In some experiments, the organizer region was killed by heat to assess the inducing ability of a dead organizer. Other experiments used natural and synthetic compounds to attempt. Although none of these experiments identified a chemical inducer with any certainty, they did discover many related properties of the developing embryo.
The epigenetic landscape is a concept representing embryonic development. It was proposed by Conrad Hal Waddington to illustrate the various developmental pathways a cell might take toward differentiation. The epigenetic landscape integrates the connected concepts of competence, induction, and regulative abilities of the genes into a single model designed to explain cellular differentiation, a long standing problem in embryology.
Hilde Proscholdt Mangold was a doctoral student at the Zoological Institute at the University of Freiburg in Freiburg, Germany, from 1920-1923. Mangold conducted research for her dissertation 'On the Induction of Embryonic Primordia by Implantation of Organizers from Different Species' ('Ueber Induktion von Embryonanlagen durch Implantation artfremder Organisatoren'), under the guidance of Hans Spemann, a professor of zoology at the University of Freiburg. The dissertation was the culmination of five experiments on three species of newt embryos, of the genus Triton (presently, Triturus), performed during the summers of 1921 and 1922, which resulted in a confirmation of Spemann's organizer concept. Spemann and Mangold published the dissertation in a 1924 edition of Roux's Archives for Microscopic Anatomy and Developmental Mechanics (Roux's Archiv fur Mikroskopische Anatomie und Entwicklungsmechanik)."