-210 Nottingham - Nottingham eTheses - The University of Nottingham

cytoplasm which contained the nucleus then resumed division and developed into a
separate but whole embryo. This experiment showed that at least in these early stages
of development, the nuclei maintained their ability to direct development of a
complete individual.
Robert Briggs and Thomas King (1952) began to establish a method to test whether
the nuclei in the dividing embryonic (blastula) cells are equivalent. They transplanted
a nucleus from a differentiated cell into an enucleated frog egg and some of the
developing embryos showed signs of gastrulation. But their subsequent experiments
showed that endoderm nuclei did not support development (Briggs and King, 1957).
However, in 1962 John Gurdon produced adult Xenopus following transplantation of
tadpole intestinal epithelial cells into enucleated eggs
(Gurdon, 1962). These
experiments brought about more experiments of differentiation (Appendix 1).
Even though John Gurdon demonstrated that differentiated cells can support
development suggesting that no changes had occurred in the genome, no adult frogs
have yet been produced using adult frog somatic cells until the end of last century
(Gurdon and Byrne, 2002; Gurdon, 2006).
1.1.2 Mammalian experiments
Embryo splitting was very popular during 1970s and 1980s and live young were
produced from isolated single blastomeres in several species including mice (Müllen
et at, 1970) and sheep (Willadsen, 1979). Offspring were also produced from
demi-embryos in mice (Tarkowski, 1959; Tsunoda and McLaren, 1983; Kim et al.,
1990), rabbits (Moore et at, 1968), sheep (Willadsen and Fehilly, 1983), goats
(Tsunoda et at, 1984), cattle (Ozil et at, 1982; Lehn-Jensen and Willadsen, 1983;
Loskutoff et at, 1989), horses (Allen and Pashen, 1984), pigs (Rorie et al., 1985) and
humans (Trounson and Mohr, 1983; Handyside et al., 1990). Normal animals were
also produced using embryos containing one-fourth of the original cell number in
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