The Nobel Prize in Physiology or Medicine 1935
"for his discovery of the organizer effect in embryonic development"
Hans Spemann (1869 - 1941) won the Noble Prize in 1935 for his contributions to developmental biology. He worked mostly with the eggs of newts and frogs and through careful observation of the developing embryo he was able to work out the fate of many cells in the early embryo.
Spemann reasoned that some cells in the early embryo were able to direct the fate of other cells. By transplanting parts of one embryo to specific locations in another embryo he determined which cells acted as organizing centers, presumably by secreting regulatory molecules [see Monday's Molecule #126 and The Spemann–Mangold organizer experiment in 1924].
Here's an excerpt from the Presentation Speech.
Much thought has been given to the nature of the forces and causality regulating this development. It is at this point that Spemann's researches begin. He used eggs of various animal species which differ in colour, and with his simple instruments transplanted small pieces of tissue in different stages of development. By this means he was able to establish that, for example, a cell mass normally destined to become ventral epidermis - Spemann calls it presumptive ventral epidermis -could develop into nerve tissue if it were put in the place where the spinal cord was to develop. Hence, the course of development of these cells was not laid down in advance or it could - if such was the case - be altered by transplantation; so that the transplanted portion adjusted itself to its new environment. When Spemann then transplanted the anterior lip of the blastopore of an embryo into the ventral side of another embryo it grew a new brain and spinal cord. This brain and spinal cord did not arise from the transplanted cell material, but from the presumptive ventral epidermis whose course of development was thus altered by the presence of the blastopore. From this Spemann could ascertain that the blastopore had an organizing influence on its environment. The cell material which was grafted into the ventral epidermis and caused the development of the new spinal cord was actually of the kind that, developing normally, would have given rise to the notochord. Further experiments showed that it is the notochord primordia which organize the development of the primordial spinal cord, while, on the other hand, the mesoderm in the head causes the development of a primordial brain. Near this arise the so-called optic vesicles which are the origin of the retina of the eye. Where these approach the ectoderm of the head they organize the development of the lens of the eye. Or, to take another example: the anterior end of the primordial gut (the oesophagus) organizes the development of a primordial mouth and primordial teeth inside it. Thus, we now see how cell masses originally undifferentiated have the course of their development laid down by the influence of rudiments of organs formed earlier. Thereafter, a cell mass such as this can assume the role of organizer in relation to its environment.
In this way we begin to understand how the laws of development work. We begin to perceive why a primordial head arises at the anterior end of the embryo, why a brain always arises in the head and never anywhere else, or why the mouth always has its place below the primordial brain and never elsewhere.
[Image Credit: E. M. De Robertis and Hiroki Kuroda (2004)]
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