In the nuclear transplantation experiment, nuclei from a frog blastula, skin cell or gut epithelial cell were transferred to an unfertilized egg without a nucleus. The nucleus was removed via: irradiation (UV exposure) that destroyed the nucleic information within the unfertilized egg; or surgical excision. Very rarely, the fertilized egg with the transferred nucleus would develop into a mature tadpole.
Similarly, the cloned sheep Dolly was created by injecting an enucleated oocyte with the nucleus of a cell scraped from an udder. These engineered oocytes were implanted into hundreds of surrogate mothers, similarly revealing the totipotency (can give rise to whole individual) of adult mammalian nuclei. As a side-note, in a revealing look at the role of nurture (as opposed to nature) Dolly looked different than the nucleus donor.
|Enucleation||Exposing ova to UV radiation enucleates them by destroying genetic material.|
|Transplant||Transplant nuclei from a frog blastula into an enucleated ovum.|
|Observe||Upon fertilization, the ovum develops normally despite the transplanted nucleus.|
|Transplant||Transplant nuclei from a differentiated cell (dermal, epithelial, etc) into enucleated ovum.|
|Observe||The ovum can still give rise to an embryo regardless of the nucleic donor's tissue type.|
|Conclusion||Enucleation and nucleic transplantation almost always kills the ovum, but the rare cases of survival still show that the nucleus is the agent responsible for blastomere totipotency.|