Transplantation Experiments: Each cell contains a full set of genetic instructions Created by: GPS • A test was carried out in 1952 by American Embryologists Robert Briggs and Thomas King • Tested the hypothesis resulting from the Hammerling’s experiments • The nucleus is the location of all heredity information in a cell •The Procedure •Briggs and King removed the nucleus from a frog egg using a glass pipette and a microscope. Could also be destroyed by UV light. •The egg did not develop •When the nucleus was replaced with one removed from a more advanced frog embryo cell… •The egg developed into an adult •Result: The nucleus was directing the eggs development into an adult frog Can every nucleus in an organism direct the development of an entire adult individual? •This was not answered definitely, because the nuclei they transplanted from frog embryos into eggs often caused the eggs to develop abnormally •Soon afterward, two more experiments were performed Successfully Transplanting Nuclei •John Gurdon (worked with South African clawed frogs ("Xenopus laevis") at Yale and Oxford) transplanted nuclei from a tadpole cell into eggs from which the nuclei had been removed. •It was necessary to synchronize the division cycles of donor and host. •In many of these experiments, the eggs developed normally. •Indicates that the nuclei of cells in later stages of development retain genetic information necessary to direct development of all other cells in an individual. John Gurdon •In 1962, Gurdon announced that he had used the nucleus of fully differentiated adult intestinal cells to clone South African clawed frogs ("Xenopus laevis"). This was the first demonstration in animals that the nucleus of a differentiated somatic cell retains the potential to develop into all cell types. Is totipotent and paved the way for future somatic cell nuclear transfer experiments, including the 1996 cloning of the sheep, Dolly. •Gurdon believed that the tadpoles were old enough so that cells taken from them would be differentiated. He exposed a frog egg to ultraviolet light, which destroyed its nucleus, then removed the nucleus from the tadpole intestinal cell and implanted it in the enucleated egg. The egg grew into a tadpole that was genetically identical to the DNA-donating tadpole, but the tadpoles cloned in early experiments never survived to adulthood. In later work, however, Gurdon successfully produced sexually mature adult frogs from eggs into which genetically marked nuclei had been transplanted from differentiated tadpole cells. Totipotency in Plants •F.C. Steward (Cornell University in 1958) placed small fragments of fully developed carrot tissue (isolated from part of the phloem) in a flask containing liquid growth medium. •Observed that when individual cells broke away from the fragments, they divided and developed multicellular roots. Totipotency in Plants Continued.. •Steward immobilized the roots by placing them in a solid growth medium. •The roots developed normally into entire, mature plants •Results: Even in adult tissues, the nucleus of individual plant cells are “totipotent” meaning that each contains a full set of heredity instructions and can generate an entire adult individual.