Box 1 | The Spemann–Mangold organizer experiment in 1924

From the following article:

Spemann's organizer and self-regulation in amphibian embryos

Edward M. De Robertis

Nature Reviews Molecular Cell Biology 7, 296-302 (April 2006)

doi:10.1038/nrm1855

The photograph shows that when a small region of the embryo, the dorsal lip (albino cells in this case), is grafted to the opposite (ventral) side of a host gastrula embryo (see embryo on the left; note that the host's dorsal lip can also be seen), the resulting Xenopus laevis tadpole develops a Siamese twin 3 days later. X. laevis is an African clawed frog that is favoured in modern research because it lays eggs year-round. Hilde Mangold (neé Proescholdt), a graduate student with Hans Spemann at Freiburg University, Germany, used salamander eggs of species that differed in their pigmentation. Because the fate of the transplanted cells could therefore be traced during development, Spemann and Mangold5 were able to demonstrate that the graft became notochord, yet induced neighbouring cells to change fates. These neighbouring cells adopted differentiation pathways that were more dorsal, and produced tissues such as the central nervous system, somites and kidneys. Note that the transplanted cells 'organize' a perfect dorsal–ventral and antero–posterior pattern in the induced tissues. The Spemann–Mangold experiment firmly established the key importance of cell–cell inductions during animal development. Hilde Proescholdt married embryologist Otto Mangold, had a baby boy, and died tragically a few months later at the age of only 26, just before her landmark paper was published. For photographs of Hans Spemann and Hilde Mangold and a re-enactment of their transplantation experiment as carried out by the author, see Supplementary information S1 (movie). The image is reproduced, with permission, from Ref. 19 © (2004) Annual Reviews.

Spemann's organizer and self-regulation in amphibian embryos