The first reported case of successful cloning was in 1952 with a tadpole. Briggs and King (1952) used nuclei from Blastula stage embryos. The host unfertilized egg was first enucleated. The blastula stage donor nucleus was removed from the embryo blastomere using a micropipet and then microinjected into the enucleated egg cytoplasm. This experiment was repeated 100-200 times. The injected host eggs activated, started to cleave and in many cases (80%) developed into swimming tadpoles. The blastula nuclear genome was directing the development of the new embryo up to the tadpole stage. Therefore, blastula nuclei appear to be totipotent.
Gurdon (1962) used donor nuclei from older tadpole differentiated intestinal cells. The rest of the procedure was the same as shown above. A small number (2-5%) of the nuclear tranplants developed into swimming tadpoles. The problem is, did Gurdon inject an intestinal cell nucleus? Remember, the PGCs are migrating out of the gut of the tadpole. Gurdon may have used a PGC nucleus and not an intestinal cell nucleus in the transplant. Even with the poor results, Gurdon claimed that fully-differentiated intestinal nuclei are still totipotent
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