28
J . B. GURDON
Altogether seven regions of the chromosome set were examined. In
three of these no change in puff pattern occurred after transplantation.
In two cases the same change was observed as would have taken place in
3 h of normal development, and in one case a puff which would normally
have appeared in 3 h of development failed to do so after transplantation. In these cases no positive effect of the changed nuclear environment was seen. However in the last case, chromosome II R section 22,
no puff appears in normal larval development, nor did it do so in the
incubated control salivary gland. However, after transplantation to
preblastoderm embryo exudate a large puff appeared in this region, but
did not do so if nuclei were transplanted to blastoderm exudate.
Although this puff appears to be specifically induced by a certain kind
of cytoplasm, this result must be interpreted cautiously since Becker
(1959) has shown puffs can occasionally be induced by culturing glands
in saline medium. However this very interesting experiment is at least
consistent with the reversible activation of genes during development.
C. Nuclear or Cytoplasmic Control of Differentiation
1. Amoeba
Two species of Amoeba have been extensively used by Danielli et ai.
(1955, etc.) to find out whether various characters which distinguish
different species or strains are determined by the nucleus or cytoplasm.
A nucleus from one species is transplanted to the enucleated cytoplasm
of another, using the methods outlined above (Section II). Although
95% of the nuclear transfers between individuals of the same species
are successful, less than 1% of those between different species give rise
to viable clones, which, however, remain viable for many hundreds of
divisions over several years. After such long periods the cytoplasmic
components of the original transplant individual must have been
diluted out, and the clones are then scored for their similarity to either
'parent species' in respect of different characters as summarized in
Table IV. All the characters of these heterotransfer clones show some
resemblance to both 'parent species'. However some, like the reaction
to antisera (which probably reflects the structure of surface proteins),
are most like those of the nuclear parent, while others, such as the size
of the nucleus, are most like those of the cytoplasmic parent. On the
basis of these results, Danielli et ai. (1955) have suggested the general
hypothesis that the nucleus determines the specific characters of the
macromolecules which are present in a differentiated cell, whereas the
organization of these macromolecules into functional units depends to
a very marked degree upon cytoplasmic inheritance. As these authors
point out, their results are consistent with other hypotheses than the
J . B. GURDON
Altogether seven regions of the chromosome set were examined. In
three of these no change in puff pattern occurred after transplantation.
In two cases the same change was observed as would have taken place in
3 h of normal development, and in one case a puff which would normally
have appeared in 3 h of development failed to do so after transplantation. In these cases no positive effect of the changed nuclear environment was seen. However in the last case, chromosome II R section 22,
no puff appears in normal larval development, nor did it do so in the
incubated control salivary gland. However, after transplantation to
preblastoderm embryo exudate a large puff appeared in this region, but
did not do so if nuclei were transplanted to blastoderm exudate.
Although this puff appears to be specifically induced by a certain kind
of cytoplasm, this result must be interpreted cautiously since Becker
(1959) has shown puffs can occasionally be induced by culturing glands
in saline medium. However this very interesting experiment is at least
consistent with the reversible activation of genes during development.
C. Nuclear or Cytoplasmic Control of Differentiation
1. Amoeba
Two species of Amoeba have been extensively used by Danielli et ai.
(1955, etc.) to find out whether various characters which distinguish
different species or strains are determined by the nucleus or cytoplasm.
A nucleus from one species is transplanted to the enucleated cytoplasm
of another, using the methods outlined above (Section II). Although
95% of the nuclear transfers between individuals of the same species
are successful, less than 1% of those between different species give rise
to viable clones, which, however, remain viable for many hundreds of
divisions over several years. After such long periods the cytoplasmic
components of the original transplant individual must have been
diluted out, and the clones are then scored for their similarity to either
'parent species' in respect of different characters as summarized in
Table IV. All the characters of these heterotransfer clones show some
resemblance to both 'parent species'. However some, like the reaction
to antisera (which probably reflects the structure of surface proteins),
are most like those of the nuclear parent, while others, such as the size
of the nucleus, are most like those of the cytoplasmic parent. On the
basis of these results, Danielli et ai. (1955) have suggested the general
hypothesis that the nucleus determines the specific characters of the
macromolecules which are present in a differentiated cell, whereas the
organization of these macromolecules into functional units depends to
a very marked degree upon cytoplasmic inheritance. As these authors
point out, their results are consistent with other hypotheses than the