Figure 43.10 Spemann’s ExperimentIn 1902, Hans Spemann tested the hypothesis that cytoplasmic factors necessary for amphibian development are segregated within the fertilized egg. Spemann performed several experiments in which he used a strand of hair from his baby daughter to constrict a fertilized salamander egg along the plane of the first cleavage. In one instance the constriction bisected the gray crescent, while in another he constricted the egg such that that gray crescent was restricted to one half of the zygote. He then allowed the halves to develop further. Results showed that only the halves containing material from the gray crescent developed normally. By comparison, halves from which the gray crescent was restricted only formed what Spemann referred to as a “bauchstück,” or belly piece, consisting of only ventral tissues with no axial structures. The results from these and similar experiments led Spemann to conclude that cytoplasmic factors in the amphibian gray crescent are essential for normal development. Spemann continued his work with salamanders and, in 1928, performed the first animal cloning experiment using just a baby’s hair and a pair of tweezers. Spemann constricted the hair around a newly fertilized egg, forcing the nucleus to one side and the cytoplasm on the other, and preventing cell material to pass between each isolated side. Then at the 16-cell stage the hair was loosened, allowing the nucleus from one of the embryo cells to move over into the piece of cytoplasm on the other side. Spemann then retighted the hair and physically separated the piece of cytoplasm and its newly-acquired nucleus from the rest of the embryo. This single cell developed into a normal salamander embryo. These results indicated that the nucleus from an early embryo had the capacity to direct the complete development of an independent salamander. In 1938 Spemann published the results of his experiments and proposed “a fantastical experiment”—the cloning of an adult cell using the nuclear transfer method.
Science for the People: A Baby’s Hair
The University of Utah: Genetic Science Learning Center: 1902—Slimy
Salamanders Cloned: What’s Next (View Time Period Movieclip)
The University of Utah: Genetic Science Learning Center: 1928—It’s
True: The Nucleus is in Charge (View Time Period Movieclip)
Howard Hughes Medical Institute: Solving the Puzzle of the Resilient Embryo
Nobelprize.org: Hans Spemann The Nobel Prize in Physiology or Medicine
Figure 43.11 The Dorsal Lip Induces Embryonic OrganizationThe findings from Hans Spemann’s early experiments in which he constricted fertilized salamander eggs with a baby’s hair led to the hypothesis that dividing cells in the early embryo each receive a different suite of cytoplasmic factors, and that these factors lead to different developmental cell fates. The results from various transplantation experiments supported this idea and led Spemann and his student, Hilde Mangold to expand upon his original hypothesis and propose that some cells can induce other cells to follow a specific developmental path. Continuing with transplantation experiments, Spemann and Mangold transplanted early gastrula dorsal lip material into the presumptive ventral epidermis of a host gastrula. The transplanted dorsal lip induced a second site of gastrulation in the host embryo, the subsequent development of dorsal structures, and finally the formation of a complete secondary embryo attached to the first embryo. Today, we know that the formation of the secondary embryo from the ventral cells of the host arose as a result of signaling molecules present in the tissue dubbed as Spemann’s organizer. Recent studies have identified a number of factors that play a role in the inductive properties of the organizer. The precise mechanism by which the organizer region forms and directs the formation of the animal body plan, however, has yet to be elucidated.
Developmental Biology 8e: A Selective History of Induction II: A. Spemann’s
Induction Experiments, B. Spemann and Mangold: The Organizer
John Kimball’s Home Page: Organizing the Embryo: The Central Nervous
System: The Spemann Organizer
International Journal of Developmental Biology: Heritage of the 1924 article
by Hans Spemann and Hilde Mangold
R&D Systems: ADMP: A Ventralizing BMP in the Dorsal Embryo