8
J. B . G U R D O N
which a wide range of genetic mutants have been isolated. Limitations
in the present form of the technique include the large amount of cytoplasm and the undefined number of nuclei that are injected. The
inability to enucleate the recipient cells is not a serious limitation, since
spores have been obtained from the injected nuclei as well as from the
host nuclei (Wilson, 1963).
4. Amoeba
Comandon and de Fonbrune (1939) devised a method of enucleation
and nuclear transplantation in Amoeba; this has been improved by
Lorch and Danielli (1953).f The amoebae to be operated on are placed
in a paraffin chamber in shallow hanging drops of Chalkley's saline
medium (including a minute amount of protein from one cytolysed
amoeba). An amoeba is enucleated by pushing its nucleus out with a
blunt glass needle (Fig. 3, A-C). Such enucleated amoebae soon lose
contact with the coverslip and show unco-ordinated streaming of the
endoplasm, but survive for 10 days or more. Nuclear transplantation is
carried out by holding two amoebae close together with a glass hook
and then pushing a nucleus from one to the other with a blunt glass
needle. After receiving a nucleus, an enucleated amoeba soon attaches
to the glass and recommences co-ordinated streaming. Reactivation
sometimes takes place within seconds but only does so after several
hours if damage was done during the operation. Only a small amount of
cytoplasm is usually carried over with the nucleus. Following nuclear
transfer there is an average delay of 1-2 days before division in addition
to the 3-4 days' delay in non-operated amoebae randomly selected
from the culture. About 95% of the nuclear transfers between individuals
of the same species are successful (Danielli et al., 1955). Nuclear transplantation in Amoeba has been extensively used by Danielli and cooperators to determine the relative contribution of nucleus and cytoplasm in the control of differentiation (Section I I I , C) as well as by
Goldstein to follow the movement of substances between nucleus and
cytoplasm (Section III, D).
5. Acetabularia
Acetabularia is a green alga which consists during most of its life cycle
of a branched rhizoid, containing a single large nucleus, a lengthy
stalk, and a cap the shape of which helps to distinguish one species from
another (Fig. 4, A, B). Two methods of transplanting nuclei have been
used in Acetabularia. One involves the transfer of an almost isolated
nucleus (Section II, B). The earlier method, which has been used more
extensively, consists of making rhizoid grafts (Hämmerling, 1934). Two
t The technique of nuclear transplantation in amoeba has been reviewed recently by
Goldstein (1963b).
J. B . G U R D O N
which a wide range of genetic mutants have been isolated. Limitations
in the present form of the technique include the large amount of cytoplasm and the undefined number of nuclei that are injected. The
inability to enucleate the recipient cells is not a serious limitation, since
spores have been obtained from the injected nuclei as well as from the
host nuclei (Wilson, 1963).
4. Amoeba
Comandon and de Fonbrune (1939) devised a method of enucleation
and nuclear transplantation in Amoeba; this has been improved by
Lorch and Danielli (1953).f The amoebae to be operated on are placed
in a paraffin chamber in shallow hanging drops of Chalkley's saline
medium (including a minute amount of protein from one cytolysed
amoeba). An amoeba is enucleated by pushing its nucleus out with a
blunt glass needle (Fig. 3, A-C). Such enucleated amoebae soon lose
contact with the coverslip and show unco-ordinated streaming of the
endoplasm, but survive for 10 days or more. Nuclear transplantation is
carried out by holding two amoebae close together with a glass hook
and then pushing a nucleus from one to the other with a blunt glass
needle. After receiving a nucleus, an enucleated amoeba soon attaches
to the glass and recommences co-ordinated streaming. Reactivation
sometimes takes place within seconds but only does so after several
hours if damage was done during the operation. Only a small amount of
cytoplasm is usually carried over with the nucleus. Following nuclear
transfer there is an average delay of 1-2 days before division in addition
to the 3-4 days' delay in non-operated amoebae randomly selected
from the culture. About 95% of the nuclear transfers between individuals
of the same species are successful (Danielli et al., 1955). Nuclear transplantation in Amoeba has been extensively used by Danielli and cooperators to determine the relative contribution of nucleus and cytoplasm in the control of differentiation (Section I I I , C) as well as by
Goldstein to follow the movement of substances between nucleus and
cytoplasm (Section III, D).
5. Acetabularia
Acetabularia is a green alga which consists during most of its life cycle
of a branched rhizoid, containing a single large nucleus, a lengthy
stalk, and a cap the shape of which helps to distinguish one species from
another (Fig. 4, A, B). Two methods of transplanting nuclei have been
used in Acetabularia. One involves the transfer of an almost isolated
nucleus (Section II, B). The earlier method, which has been used more
extensively, consists of making rhizoid grafts (Hämmerling, 1934). Two
t The technique of nuclear transplantation in amoeba has been reviewed recently by
Goldstein (1963b).