![]() ![]() 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. In the first three decades of the twentieth century, Hans Spemann experimented and led graduate students in conducting experiments with South African clawed frog embryos ( Xenopus laevis) and newt embryos ( Triturus taeniatus and Triturus cristatus). Spemann also developed the microtools needed for early experimental embryology, namely glass needles and micropipettes. To make a glass needle, Spemann held a glass rod over a burner and pulled it apart so that it became incredibly thin in the middle. The thin needle-like part of the rod was broken off, and then placed over a smaller burner called a micro-burner, another one of Spemann’s inventions. When heated and drawn a second time, the needle had an even finer point that allowed experimental embryologists to take embryos out of the jelly membranes in which they were ensconced. Additionally, Spemann created micropipettes that relied on the suction created by a piece of rubber covering the top of the hollow, thin glass rod. The rubber could be depressed by the thumb of the user to create a minute amount of suction and was useful for transplantation experiments. Experimental embryologists used micropipettes to remove cells from developing gastrulas, and transplant the cells to new sites. ![]() Prior to the Spemann-Mangold organizer experiment, Spemann had focused on constricting salamander eggs at the blastopore lip by tying single strands of his baby son’s hair around the tiny eggs. Spemann observed that when the hair tightly constricted the eggs at the dorsal end, across the blastopore lip, two embryos developed. Spemann also tested the degree to which constricting the embryo with hair led to different levels of conjoinment. For example, when Spemann constricted the eggs only a little, two heads formed, but if he pulled the hair strand tighter, the embryos developed separate heads and sets of forelimbs. However, when Spemann conducted the same experiment but separated the dorsal end from the ventral end by constriction, only the dorsal end developed, while the other half was left in a vegetative state.īuilding on those initial experiments, Spemann investigated how cell fates were determined during embryogenesis. Spemann was particularly interested in exploring the mechanism of neural plate induction. The neural plate is the embryonic structure that gives rise to the central nervous system during development. ![]() To explore neural plate induction, Spemann first performed a transplant experiment that was nearly identical to the later organizer experiment. Spemann transplanted the blastopore lip from one newt gastrula into another, and noticed a second notochord that developed at the site of transplantation. However, the newts were of the same species and it was difficult to determine whether the host tissue or transplanted tissue was acting to create the second nervous system.īased on the intra-species transplantation experiments, Spemann hypothesized that the cells at the blastopore lip were composed of ectoderm. The rationale was that the transplanted cells appeared to assimilate with the ectoderm of the host’s cells to form neural structures. Spemann also believed the cells at the blastopore lip became determined in their fate first, and that fixed determination then spread outward from that blastopore lip across the ectoderm. Spemann was mistaken, however, as the organizer experiment would later demonstrate. The mesoderm cells of the blatopore lip invaginate over the course of gastrulation and are subjacent to the ectoderm.Ĭells at the blastopore lip are not ectoderm, but mesoderm. ![]()
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