In 1997, Ian Wilmut announced that a sheep had been cloned from a somatic cell nucleus from an adult female sheep. This was the first time that an adult vertebrate had been successfully cloned from another adult. To do this, Wilmut and his colleagues 1997 took cells from the mammary gland of an adult (6-year-old) pregnant ewe and put them into culture.
The culture medium was formulated to keep the nuclei in these cells at the resting stage of the cell cycle (G0). They then obtained oocytes (the maturing egg cell) from a different strain of sheep and removed their nuclei. The fusion of the donor cell and the enucleated oocyte was accomplished by bringing the two cells together and sending electrical pulses through them. The electric pulses destabilized the cell membranes, allowing the cells to fuse together. Moreover, the same pulses that fused the cells activated the egg to begin development. The resulting embryos were eventually transferred into the uteri of pregnant sheep. Of the 434 sheep oocytes originally used in this experiment, only one survived: Dolly
DNA analysis confirmed that the nuclei of Dolly's cells were derived from the strain of sheep from which the donor nucleus was taken (Ashworth et al. 1998; Signer et al. 1998). Thus, it appears that the nuclei of adult somatic cells can be totipotent. No genes necessary for development have been lost or mutated in a way that would make them nonfunctional. This result has been confirmed in cows (Kato et al. 1998) and mice (Wakayama et al. 1998). In mice, somatic cell nuclei from the cumulus cells of the ovary were injected directly into enucleated oocytes. These renucleated oocytes were able to develop into mice at a frequency of 2.5% . Interestingly, nuclei from other somatic cells (such as neurons or Sertoli cells) that are similarly blocked at the G0 stage did not generate any live mice. Cumulus cell nuclei from cows have also directed the complete development of oocytes into mature cows
The culture medium was formulated to keep the nuclei in these cells at the resting stage of the cell cycle (G0). They then obtained oocytes (the maturing egg cell) from a different strain of sheep and removed their nuclei. The fusion of the donor cell and the enucleated oocyte was accomplished by bringing the two cells together and sending electrical pulses through them. The electric pulses destabilized the cell membranes, allowing the cells to fuse together. Moreover, the same pulses that fused the cells activated the egg to begin development. The resulting embryos were eventually transferred into the uteri of pregnant sheep. Of the 434 sheep oocytes originally used in this experiment, only one survived: Dolly
DNA analysis confirmed that the nuclei of Dolly's cells were derived from the strain of sheep from which the donor nucleus was taken (Ashworth et al. 1998; Signer et al. 1998). Thus, it appears that the nuclei of adult somatic cells can be totipotent. No genes necessary for development have been lost or mutated in a way that would make them nonfunctional. This result has been confirmed in cows (Kato et al. 1998) and mice (Wakayama et al. 1998). In mice, somatic cell nuclei from the cumulus cells of the ovary were injected directly into enucleated oocytes. These renucleated oocytes were able to develop into mice at a frequency of 2.5% . Interestingly, nuclei from other somatic cells (such as neurons or Sertoli cells) that are similarly blocked at the G0 stage did not generate any live mice. Cumulus cell nuclei from cows have also directed the complete development of oocytes into mature cows
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