Explain role of spemann’s organizers in frog.
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The first instance of cloning dated back over one hundred years ago in 1885 with the cloning of a sea urchin by Hans Dreisch. From here Hans Speman conducted the first nuclear transfer experiment in 1902 by splitting a two-celled salamander embryo into separate cells using a single strand of hair from his own child's head. In 1952 Robert Briggs and Thomas King used the nuclear transfer technology found by Speman to clone frogs from adult donor cells. However, it was only in 1963 when the word 'clone' was introduced by J.B.S. Haldane. In 1973 Tong Dizhou created the first inter-species clone by inserting Asian carp DNA into a European crucian carp. Through the many years of researching cloning Ian Wilmut cloned the very first mammal from an adult cell in 1997 with a sheep named Dolly. The cloning of Dolly was a breakthrough in cloning research and started many public debates about cloning of humans.
The Spemann-Mangold organizer, also known as the Spemann organizer, is a cluster of cells in the developing embryo of an amphibian that induces development of the central nervous system. Hilde Mangold was a PhD candidate who conducted the organizer experiment in 1921 under the direction of her graduate advisor, Hans Spemann at the University of Freiburg in Freiburg, Germany. The discovery of the Spemann-Mangold organizer introduced the concept of induction in embryonic development. Now integral to the field of developmental biology, induction is the process by which the identity of certain cells influences the developmental fate of surrounding cells. 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.
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