10
J. B. GURDON
algae are cut just above the nucleus. The two rhizoids, each containing
a nucleus, are exchanged and induced to fuse by sliding the cut end of a
rhizoid a short way into the recipient stalk and cap. It is possible to
graft several rhizoids to the branches of the rhizoid of one individual
and thus produce an alga with several nuclei which may be from
different species (Hämmerling, 1953). In practised hands 95% of the
rhizoid grafts are successful. This technique has proved very informative in analysing the release and stability of morphogenetic substances
from the nucleus (Section III, D).
6. Stentor
Tartar (1953) has developed a method of transplanting nuclei in a
ciliate protozoan called Stentor, most species of which are conical in
shape and have a string of macronuclear nodes extending along one side
of the organism (Fig. 2). Although these ciliates are only 0-1-0-3 mm
long, the favourable consistency of their endoplasm enabled Tartar to
cut out the string of nuclear nodes using fine glass needles. After the
wound has healed, a small piece of endoplasm containing two or three
nuclear nodes is cut out of another individual and pushed into a slit
made in the enucleated host. The operation is carried out in a viscous
solution of methyl cellulose (which is apparently harmless) dissolved in
sterile filtered lake water. An appreciable amount of cytoplasm is
transplanted with the nuclei as well as some of the very small micronuclei normally situated close to the macronuclei. The majority of
nuclear grafts are successful.
The kind of nuclear transfer experiments so far carried out in Stentor
result in alterations in the normal volume ratio of nucleus and cytoplasm, and also in the combination of nucleus and cytoplasm from different varieties (Section III, C). Greatly increased or decreased volume
ratios of nucleus and cytoplasm result only in retarded regeneration
(Tartar, 1960). Therefore the function of the cell is not dependent
upon a precise nucleo-cytoplasmic volume ratio. Regeneration following
excision of some of the macronuclear nodes has shown that each node
in the macronuclear string is functionally equivalent (Tartar, 1961).
There is therefore no evidence of any intranuclear differentiation along
the macronucleus in this organism.
B. Transfer of Isolated Nuclei
In all the cases discussed above where nuclei have been successfully
transplanted, some cytoplasm is injected with the nucleus, even though
this may be only a minute fraction of the volume of cytoplasm of the
host cell as in Amphibia. Indeed many authors have commented on the
fact that it is essential for the survival of the transplanted nucleus that
J. B. GURDON
algae are cut just above the nucleus. The two rhizoids, each containing
a nucleus, are exchanged and induced to fuse by sliding the cut end of a
rhizoid a short way into the recipient stalk and cap. It is possible to
graft several rhizoids to the branches of the rhizoid of one individual
and thus produce an alga with several nuclei which may be from
different species (Hämmerling, 1953). In practised hands 95% of the
rhizoid grafts are successful. This technique has proved very informative in analysing the release and stability of morphogenetic substances
from the nucleus (Section III, D).
6. Stentor
Tartar (1953) has developed a method of transplanting nuclei in a
ciliate protozoan called Stentor, most species of which are conical in
shape and have a string of macronuclear nodes extending along one side
of the organism (Fig. 2). Although these ciliates are only 0-1-0-3 mm
long, the favourable consistency of their endoplasm enabled Tartar to
cut out the string of nuclear nodes using fine glass needles. After the
wound has healed, a small piece of endoplasm containing two or three
nuclear nodes is cut out of another individual and pushed into a slit
made in the enucleated host. The operation is carried out in a viscous
solution of methyl cellulose (which is apparently harmless) dissolved in
sterile filtered lake water. An appreciable amount of cytoplasm is
transplanted with the nuclei as well as some of the very small micronuclei normally situated close to the macronuclei. The majority of
nuclear grafts are successful.
The kind of nuclear transfer experiments so far carried out in Stentor
result in alterations in the normal volume ratio of nucleus and cytoplasm, and also in the combination of nucleus and cytoplasm from different varieties (Section III, C). Greatly increased or decreased volume
ratios of nucleus and cytoplasm result only in retarded regeneration
(Tartar, 1960). Therefore the function of the cell is not dependent
upon a precise nucleo-cytoplasmic volume ratio. Regeneration following
excision of some of the macronuclear nodes has shown that each node
in the macronuclear string is functionally equivalent (Tartar, 1961).
There is therefore no evidence of any intranuclear differentiation along
the macronucleus in this organism.
B. Transfer of Isolated Nuclei
In all the cases discussed above where nuclei have been successfully
transplanted, some cytoplasm is injected with the nucleus, even though
this may be only a minute fraction of the volume of cytoplasm of the
host cell as in Amphibia. Indeed many authors have commented on the
fact that it is essential for the survival of the transplanted nucleus that