Hans Spemann

German zoologist, embryologist, and histologist (1869–1941)

Spemann, who was born at Stuttgart in Germany, worked for a time in his father's bookshop there before graduating in zoology, botany, and physics at the universities of Heidelberg, Munich, and Würzburg. He was first an assistant, then a lecturer, at the Zoological Institute of Würzburg (1894–1908) before becoming professor at Rostock (1909–14). He was then successively associate director of the Kaiser Wilhelm Institute of Biology, Berlin (1914–19), and professor of zoology at Freiburg (1919–35).

Spemann's concept of embryonic induction, based on a lifetime's study of the development of amphibians such as newts, showed that certain parts of the embryo – the organizing centers – direct the development of groups of cells into particular organs and tissues. He further demonstrated an absence of predestined organs or tissues in the earliest stages of embryonic development; tissue excised from one part of the embryo and grafted onto another part will assume the character of the latter, losing its original nature. Spemann's highly original work, for which he received the Nobel Prize in 1935, paved the way for subsequent recognition of similar organizing centers in other animals groups. It is elaborated in Experimentelle Beiträge zu einer Theorie der Entwicklung (1936; Embryonic Development and Induction).

The German experimental embryologist Hans Spemann (1869-1941) was awarded the Nobel Prize in Physiology or Medicine for his discovery of the organizer effect in embryonic development.

Hans Spemann, son of Wilhelm Spemann, a publisher, was born in Stuttgart on June 27, 1869. After a period in his father's business and military service, he became a medical student at the University of Heidelberg, spent a period at the University of Munich, and in 1894 transferred to Würzburg. There he abandoned medicine for science, studied under Theodor Boveri, who greatly influenced his future research, and graduated in 1895.

Spemann then began research in the Zoological Institute at Würzburg, where he became a lecturer in 1898. In 1908 he was appointed professor of zoology and comparative anatomy in the University of Rostock, and in 1914 associate director of the Kaiser Wilhelm Institute for Biology at Berlin-Dahlem. He was called to the chair of zoology in the University of Freiburg in Breisgau in 1919, from which post he retired in 1935. Spemann devoted his scientific career to the study of the causes that act on the cells of the earliest embryos, leading to their differentiation and specialization for different functions.

Foundation of Experimental Embryology

The science of experimental embryology (or developmental mechanics) was founded about 1890 by Wilhelm Roux and Hans Driesch. Roux destroyed one of the two blastomeres formed by the first division of a fertilized frog's egg. He found that the other blastomere continued to develop, but it formed half an embryo. Then Driesch separated the two blastomeres of a sea urchin's egg and removed one entirely. The remaining blastomere formed, not half an embryo, but a normal embryo of small size.

It was well known that the eyeball developed from the optic cup, a protuberance from the primitive brain, and that the lens arose in the epidermis overlying the optic cup. Why the epidermis thickened and became transparent at the appropriate point was unknown, and the question was whether there was some unknown connection between optic cup and potential lens. In 1901 Carl Herbst found that, in abnormal embryos showing a single (median) optic cup, only one lens developed and that at a point opposite the cup. This strongly favored an influence exerted by the cup on the overlying ectoderm.

Spemann's Classical Experiments

This paper by Herbst fired Spemann's enthusiasm, and in the same year he demonstrated that the epidermis showed no change if the eye rudiment was destroyed. He suggested that proof of the correlation could be obtained if the optic cup was brought into contact with a foreign part of the epidermis, either by transplanting the optic cup or the epidermis overlying it. W. H. Lewis performed these experiments satisfactorily in 1904. During the next 6 years Spemann published his experiments on the eye and also his technique and instruments for "microsurgery." It was shown that practically any part of the epidermis could form a lens if it was activated by some influence in the optic cup.

Spemann then experimented on the amphibian gastrula, the early embryo consisting of undifferentiated cells forming a hollow sphere, with a mouth (the blastopore) opening to the exterior. He frequently transplanted minute pieces of the gastrula from one area of its surface to another, and he always found - with one exception - that the transplants developed according to their new positions. The exception was a transplant from the upper lip of the blastopore, which in its new position developed into a small secondary embryo. In 1918 Spemann thought that the whole of the secondary embryo was formed by the implanted material, so that the ectoderm (upper layer) of the implant formed the medullary plate (subsequently forming the central nervous system), and the lower layer developed into the notochord and muscular system. He concluded therefore that the blastopore region was already differentiated at that stage, while all other cells in the gastrula were still undifferentiated.

Further work then led Spemann to think that possibly the primitive nervous system of the secondary embryo was formed by induction from the ectoderm of the host tissue. To decide the point it was necessary to distinguish implanted tissue from host tissue. Until then his transplants had been from one part to another of the same embryo, but in 1921 he decided that the answer lay in using two embryos, of the same age but of different species. In 1924 Spemann and Hilde Mangold published their results. For the implant and the host they used respectively gastrulas of the newts Triton cristatus (almost colorless) and Triton taeniatus (highly pigmented). Implant and host cells were thus easily distinguished. In innumerable experiments they found that the graft disappeared below the gastrula surface to form the mesodermal elements (notochord and muscles) of the secondary embryo. Above it the ectoderm of the host was induced to form, from host material, the neural tube of the secondary embryo.

Organizer Effect

From these "heteroplastic transplants" Spemann concluded that the upper lip of the blastopore, when brought into contact with other cells of the gastrula, could exert an influence to induce them to become differentiated to form a medullary plate. This influence he called an "organizer." In all vertebrate embryos it is the first step in the series of differentiations that result in the fully formed fetus. He therefore termed the influence of the blastopore lip the "primary organizer." The formation of the optic cup being a sequel to this action, he called the organizer in the optic cup a "secondary organizer." Further development is due to chains of induction by successive orders of organizers. Spemann believed that the action of the organizer was transferred by a chemical substance; but he, and other scientists such as Joseph Needham and C. H. Waddington, succeeded only partially in identifying it.

Spemann was awarded the Nobel Prize in 1935, and he received many other honors, including the title of Geheimrat (Privy Councilor). He died at Freiburg on Sept. 9, 1941.

Further Reading

There is a biography of Spemann in Nobel Lectures, Physiology or Medicine, 1922-1941 (1965), which also includes his Nobel Lecture. For his work see his Embryonic Development and Induction (1938); see also C. H. Waddington, The Nature of Life (1961), and J. Needham, Biochemistry and Morphogenesis (1942).

Hans Spemann
Born	June 27, 1869(1869-06-27) Stuttgart, Germany
Died	September 9, 1941 (aged 72) Freiburg, Germany
Nationality	German
Fields	Embryology
Known for	Embryonic induction and the Organiser
Notable awards	Nobel Prize in Physiology or Medicine (1935)

Hans Spemann (June 27, 1869 – September 9, 1941) was a German embryologist who was awarded the Nobel Prize in Physiology or Medicine in 1935 for his discovery of the effect now known as embryonic induction, an influence, exercised by various parts of the embryo, that directs the development of groups of cells into particular tissues and organs.

Contents 1 Biography 2 Experiments in Ontogeny 3 Induction and Organisers 4 See also 5 References 6 External links

Biography

Hans Spemann was born in Stuttgart, the eldest son of publisher Wilhelm Spemann and his wife Lisinka, nee Hoffman. After he left school in 1888 he spent a year in his father's business, then, in 1889–1890, he did military service in the Kassel Hussars followed by a short time as a bookseller in Hamburg. In 1891 he entered the University of Heidelberg where he studied medicine, taking his preliminary examination in 1893. There he met the biologist and psychologist Gustav Wolff who had begun experiments on the embryological developments of newts and shown that, if the lens of a developing newt's eye is removed, it regenerates.

In 1892 Spemann married Klara Binder: the couple were to have two sons. In 1893–1894 he moved to the University of Munich for clinical training but decided, rather than becoming a clinician, to move to the Zoological Institute at the University of Würzburg, where he remained as a lecturer until 1908. His degree in zoology, botany, and physics, awarded in 1895, followed study under Theodor Boveri, Julius Sachs and Wilhelm Röntgen.^[1]

For his Ph.D. thesis under Boveri, Spemann studied cell lineage in the parasitic worm Strongylus paradoxus, for his teaching diploma, the development of the middle ear in the frog.^[2]

Experiments in Ontogeny

During the winter of 1896, while quarantined in a sanitarium recovering from tuberculosis, Spemann read August Weismann's book The Germ Plasm: A Theory of Heredity.^[3] He wrote in his autobiography: "I found here a theory of heredity and development elaborated with uncommon perspicacity to its ultimate consequences.....This stimulated experimental work of my own"^[4]

Results in embryology had been contradictory: in 1888 Wilhelm Roux, who had introduced the experimental manipulation of the embryo to discover the rules of development, performed a series of experiments in which he inserted a hot needle into one of two blastomeres to kill it. He then observed how the remaining blastomere developed, and found that it became a half embryo. In 1892 Hans Driesch, performed similar experiments on sea urchin embryos, but instead of killing one of the two blastomeres he put many embryos in a tube and shook it to separate the cells. He reported that, contrary to Roux's findings, he ended up with completely-formed but smaller embryos. The reason for this discrepancy has been widely attributed to Driesch separating the two blastomeres completely rather than just killing one as Roux had done. Others, including Thomas Hunt Morgan and Oscar Hertwig, attempted to separate the two cells, for the matter was of great importance, particularly to the arguments between proponents of epigenesis and preformation, but satisfactory results could not be achieved.^[5]

As a master of micro-surgical technique, beginning with his continuing work on the amphibian eye, Spemann's papers in the early years of the 20th century on this vexed question were to be a great contribution to the development of experimental morphogenesis, causing him to be hailed in some quarters as the true founder of micro-surgery. He succeeded in dividing the cells with a noose of baby hair. Spemann found that one half could indeed form a whole embryo, but observed that the plane of division was crucial.^[6] This dispatched the theory of preformation and gave some support to the concept of a morphogenetic field, a concept of which Spemann learned from Paul Alfred Weiss.

Induction and Organisers

Hilde Mangold in 1924 - shortly afterwards she was killed in a domestic fuel explosion.

Spemann was appointed Professor of Zoology and Comparative Anatomy at Rostock in 1908 and, in 1914, Associate Director of the Kaiser Wilhelm Institute of Biology at Dahlem, Berlin. Here he undertook the experiments that would make him famous. Drawing upon the recent work of Warren H. Lewis^[7] and Ethel Browne Harvey,^[8] he turned his skills to the gastrula, grafting a "field" of cells (the Primitive knot) from one embryo onto another.

The experiments, aided by Hilde Proescholdt (later Mangold), a Ph.D. candidate in Spemann's laboratory in Freiburg, took place over several years and were published in full only in 1924. They described an area in the embryo, the portions of which, upon transplantation into a second embryo, organized or "induced" secondary embryonic primordia regardless of location. Spemann called these areas "organiser centres" or "organisers". Later he showed that different parts of the organiser centre produce different parts of the embryo.

Despite his modern reputation, Spemann continued to entertain neo-vitalist "field" analyses similar to those of Driesch, Gurwitsch and Harold Saxton Burr. However, the follow-up work of Johannes Holtfreter, Dorothy M. Needham and Joseph Needham, Conrad Waddington and others showed that organizers killed by boiling, fixing or freezing were also capable of causing induction. The conclusion was that the actual controllers were inert molecules, though little headway was made until the end of the 20th century in discovering how signalling took place.

From 1919 Spemann was Professor of Zoology at the University of Freiburg-im-Breisgau, where he continued his line of enquiry until in 1937 he was relieved of his post to be replaced by one of his first students, Otto Mangold. In 1928 he was the first to perform somatic cell nuclear transfer using amphibian embryos - one of the first moves towards cloning.^[1] He was awarded the Nobel Prize in 1935. His theory of embryonic induction by organisers is described in his book Embryonic Development and Induction (1938). He died of heart failure on 12 September 1941. He never lost his love of classical literature and, throughout his life, organized evening gatherings of friends to discuss art, literature, and philosophy.

See also

• Developmental biology
• Morphogenesis
• Theodor Boveri
• August Weismann

References

1. ^ ^{a b} Nobel Lectures, Physiology or Medicine 1922–1941, Elsevier Publishing Company, Amsterdam, 1965
2. ^ Monograph by Claudio Stern, J. Z. Young Professor and Head of the Department of Anatomy and Developmental Biology at University College London, based on Spemann, 1943; Mangold, 1953; Hamburger, 1988. See: http://www.bioinfo.org.cn/book/Great%20Experments/great30.htm (retrieved May 2008).
3. ^ Scientist Profile : Hans Spemann
4. ^ Spemann's autobiography, quoted in V. Hamburger, The Heritage of Experimental Embryology: Hans Spemann and the Organizer, 1988, Oxford University Press, Oxford, page 9.
5. ^ Stern, op. cit.
6. ^ ibid.
7. ^ ibid.
8. ^ Ethel Browne Harvey

External links

• Explanation of the Spemann-Mangold experiment from a Nature Reviews article

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