16
J. B. GURDON
evidence favouring this idea comes from Briggs and King's work on
Rana pipiens which concerns the stability and specificity of the nuclear
transplant-embryo abnormalities.
The demonstration that transplanted nuclei from differentiating cells
have undergone stable changes was provided by the serial nuclear
transplantation experiments described in a classical paper by King and
Briggs (1956). The method of serial transplantation is shown diagrammatically in Fig. 1, and involves several nuclear transfers from a
blastula which has itself been derived from a transplanted nucleus of an
original donor embryo. The following points have been established by
Briggs and King's work on Rana pipiens. When nuclei are taken from
an original blastula donor, nearly all the serial transfer generations
contain many normal tadpoles. If, on the other hand, the original donor
nucleus comes from a gastrula or later developmental stage, then the
serial transfer generations often contain embryos all of which are
abnormal and many of which are abnormal in the same way. A second
serial transfer generation made from one of these embryos again contains many embryos which are abnormal in the same way, or are more
abnormal; they never develop more normally. This shows that the
transplanted nucleus from which these serial transfer generations are
derived has undergone some restriction in developmental capacity
which is stable under the conditions of serial transplantation. One other
conclusion can be drawn from these experiments. It is found that the
serial transfer generations derived from original donor nuclei of the
same embryo may develop quite differently. One gastrula endoderm
nucleus may give serial transfer embryos all of which are normal,
whereas another endoderm nucleus from the same gastrula may give
only arrested blastulae. This shows that nuclei from the same tissue of
one embryo do not all undergo the same stable change at the same time.
Results of this kind have been obtained in Xenopus (Gurdon, 1960b) as
well as in Rana (King and Briggs, 1956), but they do not establish the
time at which these nuclear changes take place—before or after transplantation.
The specificity of the nuclear changes should answer this question. If
FIG. 5. A-L. Lethal nuclear-transplant hybrids. From Gurdon (1962b). A-F, Arrested
post-neurula embryos characteristic of Xenopus tropicalis nuclei transplanted to
enucleated eggs of Xenopus laevis. G-L. Arrested early neurula development typically
supported by Xenopus laevis nuclei which have replicated several times in Xenopus
tropicalis egg cytoplasm before being transplanted back to enucleated X. laevis eggs.
M-P. Nuclear transplant embryos in Rana pipiens. From Briggs and King (1957).
M and O, Neurula and tail-bud embryos of Rana pipiens derived from the transplantation
of late gastrula nuclei to enucleated egg cytoplasm. These embryos show the endoderm
syndrome of abnormalities described in the text. N and P are control embryos from
fertilized eggs of the same age as M and O respectively.
J. B. GURDON
evidence favouring this idea comes from Briggs and King's work on
Rana pipiens which concerns the stability and specificity of the nuclear
transplant-embryo abnormalities.
The demonstration that transplanted nuclei from differentiating cells
have undergone stable changes was provided by the serial nuclear
transplantation experiments described in a classical paper by King and
Briggs (1956). The method of serial transplantation is shown diagrammatically in Fig. 1, and involves several nuclear transfers from a
blastula which has itself been derived from a transplanted nucleus of an
original donor embryo. The following points have been established by
Briggs and King's work on Rana pipiens. When nuclei are taken from
an original blastula donor, nearly all the serial transfer generations
contain many normal tadpoles. If, on the other hand, the original donor
nucleus comes from a gastrula or later developmental stage, then the
serial transfer generations often contain embryos all of which are
abnormal and many of which are abnormal in the same way. A second
serial transfer generation made from one of these embryos again contains many embryos which are abnormal in the same way, or are more
abnormal; they never develop more normally. This shows that the
transplanted nucleus from which these serial transfer generations are
derived has undergone some restriction in developmental capacity
which is stable under the conditions of serial transplantation. One other
conclusion can be drawn from these experiments. It is found that the
serial transfer generations derived from original donor nuclei of the
same embryo may develop quite differently. One gastrula endoderm
nucleus may give serial transfer embryos all of which are normal,
whereas another endoderm nucleus from the same gastrula may give
only arrested blastulae. This shows that nuclei from the same tissue of
one embryo do not all undergo the same stable change at the same time.
Results of this kind have been obtained in Xenopus (Gurdon, 1960b) as
well as in Rana (King and Briggs, 1956), but they do not establish the
time at which these nuclear changes take place—before or after transplantation.
The specificity of the nuclear changes should answer this question. If
FIG. 5. A-L. Lethal nuclear-transplant hybrids. From Gurdon (1962b). A-F, Arrested
post-neurula embryos characteristic of Xenopus tropicalis nuclei transplanted to
enucleated eggs of Xenopus laevis. G-L. Arrested early neurula development typically
supported by Xenopus laevis nuclei which have replicated several times in Xenopus
tropicalis egg cytoplasm before being transplanted back to enucleated X. laevis eggs.
M-P. Nuclear transplant embryos in Rana pipiens. From Briggs and King (1957).
M and O, Neurula and tail-bud embryos of Rana pipiens derived from the transplantation
of late gastrula nuclei to enucleated egg cytoplasm. These embryos show the endoderm
syndrome of abnormalities described in the text. N and P are control embryos from
fertilized eggs of the same age as M and O respectively.