12
J . B. GURDON
buffer below 0-002M, as well as Chalkley's medium, allowed up to 30%
survival. These experiments provide a more stringent test of nuclear
media than does the injection of the media into whole cells, an approach
which Burnstock and Philpot also tried.
Following some preliminary experiments by Hämmerling (1955),
Werz (1962) has tried re-nucleation experiments in Acetabularia after
exposing the nucleus to various media. He found that the nuclear
membrane develops vesicles in saline and weak sucrose solutions (Fig.
4, C-E), but that this is progressively alleviated by adding sucrose to
the medium. He found that an isolated nucleus can be kept for 12 min
in a 20% sucrose solution and yet can promote normal morphogenesis
when transplanted back to an enucleated Acetabularia.
So far no artificial medium has been found in which isolated amphibian
nuclei can be kept alive for even short periods. Preliminary results in
the author's laboratory suggest that sucrose media may be less damaging
to exposed Xenopus nuclei than the currently used saline media. It is
of course very difficult to try and determine what the conditions really
are in living cytoplasm and hence how to devise an entirely harmless
nuclear medium. The empirical testing of media by nuclear transplantation seems as hopeful an approach to this problem as any other.
C. Summary
We have seen that living cell nuclei have been successfully transplanted to a new eytoplasmic environment in several quite different
organisms—Amphibia, insects, Neurospora, Amoeba, Acetabularia, and
Stentor. In Amoeba, Acetabularia, and Amphibia the technique has been
fully developed in that a single nucleus can be transplanted to an
enucleated cell and the resulting cell or organism behaves entirely
normally in a high percentage of cases.
The transplantation of nuclei from differentiating cells has only been
achieved so far in Amphibia. Nuclei from certain kinds of fully differentiated cells can be used, but it is not possible to transplant nuclei to any
other kind of cytoplasm than that of an egg, since only the egg is large
enough to withstand enucleation and penetration by a pipette. In order
FIG. 4. A-E. Acetabularia species and isolated nuclei. A, Acetabularia mediterranea,
young plant showing typical cap (c.s.) and rhizoid (r). B, Acicularia schenckii showing
typically divided cap. C, Nucleus of Acetabularia immediately after isolation in 0*1%
sucrose solution. D, Same nucleus 30 sec after isolation. E, Same nucleus 1 min after
isolation, showing vesicles on the nuclear membrane.
F-G. Injection of nuclei into Calliphora eggs. F, Blastoderm stage of Calliphora; nuclei
(dark areas) are situated peripherally. G, Feulgen stained nuclei (dark spots) in an unfertilized egg of CaUiphora 3 h after it had received a few transplanted blastoderm nuclei.
A and B from Hämmerling (1953); C-E from Werz (1962); F and G from Graham
(unpublished).
J . B. GURDON
buffer below 0-002M, as well as Chalkley's medium, allowed up to 30%
survival. These experiments provide a more stringent test of nuclear
media than does the injection of the media into whole cells, an approach
which Burnstock and Philpot also tried.
Following some preliminary experiments by Hämmerling (1955),
Werz (1962) has tried re-nucleation experiments in Acetabularia after
exposing the nucleus to various media. He found that the nuclear
membrane develops vesicles in saline and weak sucrose solutions (Fig.
4, C-E), but that this is progressively alleviated by adding sucrose to
the medium. He found that an isolated nucleus can be kept for 12 min
in a 20% sucrose solution and yet can promote normal morphogenesis
when transplanted back to an enucleated Acetabularia.
So far no artificial medium has been found in which isolated amphibian
nuclei can be kept alive for even short periods. Preliminary results in
the author's laboratory suggest that sucrose media may be less damaging
to exposed Xenopus nuclei than the currently used saline media. It is
of course very difficult to try and determine what the conditions really
are in living cytoplasm and hence how to devise an entirely harmless
nuclear medium. The empirical testing of media by nuclear transplantation seems as hopeful an approach to this problem as any other.
C. Summary
We have seen that living cell nuclei have been successfully transplanted to a new eytoplasmic environment in several quite different
organisms—Amphibia, insects, Neurospora, Amoeba, Acetabularia, and
Stentor. In Amoeba, Acetabularia, and Amphibia the technique has been
fully developed in that a single nucleus can be transplanted to an
enucleated cell and the resulting cell or organism behaves entirely
normally in a high percentage of cases.
The transplantation of nuclei from differentiating cells has only been
achieved so far in Amphibia. Nuclei from certain kinds of fully differentiated cells can be used, but it is not possible to transplant nuclei to any
other kind of cytoplasm than that of an egg, since only the egg is large
enough to withstand enucleation and penetration by a pipette. In order
FIG. 4. A-E. Acetabularia species and isolated nuclei. A, Acetabularia mediterranea,
young plant showing typical cap (c.s.) and rhizoid (r). B, Acicularia schenckii showing
typically divided cap. C, Nucleus of Acetabularia immediately after isolation in 0*1%
sucrose solution. D, Same nucleus 30 sec after isolation. E, Same nucleus 1 min after
isolation, showing vesicles on the nuclear membrane.
F-G. Injection of nuclei into Calliphora eggs. F, Blastoderm stage of Calliphora; nuclei
(dark areas) are situated peripherally. G, Feulgen stained nuclei (dark spots) in an unfertilized egg of CaUiphora 3 h after it had received a few transplanted blastoderm nuclei.
A and B from Hämmerling (1953); C-E from Werz (1962); F and G from Graham
(unpublished).