TRANSPLANTATION OF CELL NUCLEI
7
been possible to prove by use of genetic mutants that the zygote nucleus
does not participate in development.
If it can be established that the injected nuclei are responsible for the
development of the eggs, then DuPraw's experiments are the first to
show that nuclear transplantation is feasible in insects. It should not
be impossible to refine the technique so as to inject only one nucleus
with correspondingly less cytoplasm. In the author's laboratory C. F.
Graham (unpublished) has looked into the possibility of transplanting
nuclei in Drosophila and Calliphora. So far no success has been obtained
in Drosophila. In Calliphora, injected nuclei sometimes appear to divide
a few times, but development does not proceed as far as the blastoderm
stage (Fig. 4, F, G). The relatively Mosaic' nature of many insect eggs
makes it difficult to obtain normal larvae after manipulation of the egg,
but there must be other reasons which are not yet apparent why nuclei
fail to divide after transfer.
3. Neurospora
As a result of the very careful preparation of micropipettes and the
use of certain structural and physiological peculiarities of Neurospora,
Wilson (1963) has been able to transplant nuclei in this fungus. Neurospora has chains (hyphae) of elongated cells each of which contains
twenty or more free nuclei (Fig. 3, D). The cells are separated by a
septum ; this is perforated by a pore which becomes sealed off if one of
the cells on either side of it dies. Some of the contents of one cell, including several nuclei, are sucked up into a micropipette. The pipette is
then inserted into a cell of the recipient hypha in such a way that the
contents of the pipette are disgorged through the septal pore into the
neighbouring cell. The volume of cytoplasm and number of nuclei
introduced in this way generally amounts to about one-tenth of that
already present in the recipient cell. After the pipette is withdrawn the
punctured cell dies, and if the operation is successful the septum seals
itself off. About one-third of the successful transfer-heterokaryons then
commence growth.
The successful transplantation of nuclei has been proved by injecting
nuclei from a strain unable to synthesize an amino acid (or vitamin) into
cells which are unable to synthesize a different'amino acid, and showing
that the resulting heterokaryons will grow on minimal medium lacking
both amino acids. Some strains always fail to grow after injection of
nuclei from certain other strains ; this can be attributed to incompatibility—a phenomenon which can be analysed further by this technique.
The main importance of these experiments is to demonstrate the
possibility of manipulating and transplanting nuclei in Neurospora.
This is the only organism in which nuclei can be transplanted and in
7
been possible to prove by use of genetic mutants that the zygote nucleus
does not participate in development.
If it can be established that the injected nuclei are responsible for the
development of the eggs, then DuPraw's experiments are the first to
show that nuclear transplantation is feasible in insects. It should not
be impossible to refine the technique so as to inject only one nucleus
with correspondingly less cytoplasm. In the author's laboratory C. F.
Graham (unpublished) has looked into the possibility of transplanting
nuclei in Drosophila and Calliphora. So far no success has been obtained
in Drosophila. In Calliphora, injected nuclei sometimes appear to divide
a few times, but development does not proceed as far as the blastoderm
stage (Fig. 4, F, G). The relatively Mosaic' nature of many insect eggs
makes it difficult to obtain normal larvae after manipulation of the egg,
but there must be other reasons which are not yet apparent why nuclei
fail to divide after transfer.
3. Neurospora
As a result of the very careful preparation of micropipettes and the
use of certain structural and physiological peculiarities of Neurospora,
Wilson (1963) has been able to transplant nuclei in this fungus. Neurospora has chains (hyphae) of elongated cells each of which contains
twenty or more free nuclei (Fig. 3, D). The cells are separated by a
septum ; this is perforated by a pore which becomes sealed off if one of
the cells on either side of it dies. Some of the contents of one cell, including several nuclei, are sucked up into a micropipette. The pipette is
then inserted into a cell of the recipient hypha in such a way that the
contents of the pipette are disgorged through the septal pore into the
neighbouring cell. The volume of cytoplasm and number of nuclei
introduced in this way generally amounts to about one-tenth of that
already present in the recipient cell. After the pipette is withdrawn the
punctured cell dies, and if the operation is successful the septum seals
itself off. About one-third of the successful transfer-heterokaryons then
commence growth.
The successful transplantation of nuclei has been proved by injecting
nuclei from a strain unable to synthesize an amino acid (or vitamin) into
cells which are unable to synthesize a different'amino acid, and showing
that the resulting heterokaryons will grow on minimal medium lacking
both amino acids. Some strains always fail to grow after injection of
nuclei from certain other strains ; this can be attributed to incompatibility—a phenomenon which can be analysed further by this technique.
The main importance of these experiments is to demonstrate the
possibility of manipulating and transplanting nuclei in Neurospora.
This is the only organism in which nuclei can be transplanted and in