2
J. B. GURDON
In Section IV the conclusions reached from nuclear transfer experiments are compared with relevant results from other kinds of experiments. Rather few other experimental approaches yield results which
can be directly compared to those obtained from the manipulation of
living nuclei, but it is at least possible to determine how far the results
of nuclear transplantation are consistent with those of other experiments.
II. Techniques of Nuclear Transplantation
A. Transfer of Nuclei with Cytoplasm
The successful transplantation of living cell nuclei to a new cytoplasmic environment has now been achieved in several different
organisms each of which offers certain advantages for this kind of
operation. However each organism also presents some technical problems the solution of which always depends to a considerable extent on
the dexterity of the operator, as well as on the development of special
methods.
It should be pointed out at this stage that the same result as is
achieved by nuclear transplantation can sometimes be realized by
appropriate hybridization experiments. Astaurov and OstriakovaVarshaver (1957), for example, heated eggs of Bombyx mandarina
fertilized with sperm of Bombyx mori to 40° C for over 2 h. This prevented the egg nucleus in the second meiotic metaphase from leaving
the egg periphery and allowed the fusion of two sperm nuclei to give
diploid androgenetic hybrids. This method can only be used to combine
egg cytoplasm with sperm nuclei. Nuclear transplantation must therefore be employed to introduce different kinds of somatic cell nuclei to
egg cytoplasm.
1. Amphibia
Briggs and King (1952) were the first to obtain really satisfactory
results from the transplantation of blastula cell nuclei to enucleated
frog eggs. The principle of their method has been followed in all subsequently successful work with Amphibia (Fig. 1). Further details of
the techniques outlined below may be found in the following references :
Briggs and King (1953) and King and Briggs (1955) for Bana; Gurdon
(1960b) and Elsdale et al (1960) for Xenopus; Signoret et al (1962) for
Ambystoma; Signoret and Picheral (1962) for Pleurodeles.
Unfertilized eggs are laid by frogs several hours after they have received an injection of anterior pituitary glands or of gonadotrophic
hormone. In some species, unfertilized eggs require activation before
they will respond to an injected nucleus. In Xenopus no activation is
J. B. GURDON
In Section IV the conclusions reached from nuclear transfer experiments are compared with relevant results from other kinds of experiments. Rather few other experimental approaches yield results which
can be directly compared to those obtained from the manipulation of
living nuclei, but it is at least possible to determine how far the results
of nuclear transplantation are consistent with those of other experiments.
II. Techniques of Nuclear Transplantation
A. Transfer of Nuclei with Cytoplasm
The successful transplantation of living cell nuclei to a new cytoplasmic environment has now been achieved in several different
organisms each of which offers certain advantages for this kind of
operation. However each organism also presents some technical problems the solution of which always depends to a considerable extent on
the dexterity of the operator, as well as on the development of special
methods.
It should be pointed out at this stage that the same result as is
achieved by nuclear transplantation can sometimes be realized by
appropriate hybridization experiments. Astaurov and OstriakovaVarshaver (1957), for example, heated eggs of Bombyx mandarina
fertilized with sperm of Bombyx mori to 40° C for over 2 h. This prevented the egg nucleus in the second meiotic metaphase from leaving
the egg periphery and allowed the fusion of two sperm nuclei to give
diploid androgenetic hybrids. This method can only be used to combine
egg cytoplasm with sperm nuclei. Nuclear transplantation must therefore be employed to introduce different kinds of somatic cell nuclei to
egg cytoplasm.
1. Amphibia
Briggs and King (1952) were the first to obtain really satisfactory
results from the transplantation of blastula cell nuclei to enucleated
frog eggs. The principle of their method has been followed in all subsequently successful work with Amphibia (Fig. 1). Further details of
the techniques outlined below may be found in the following references :
Briggs and King (1953) and King and Briggs (1955) for Bana; Gurdon
(1960b) and Elsdale et al (1960) for Xenopus; Signoret et al (1962) for
Ambystoma; Signoret and Picheral (1962) for Pleurodeles.
Unfertilized eggs are laid by frogs several hours after they have received an injection of anterior pituitary glands or of gonadotrophic
hormone. In some species, unfertilized eggs require activation before
they will respond to an injected nucleus. In Xenopus no activation is