338
J. S E E D
consistent with the u.v. photometric measurements (Seed, 1963a). In
HeLa cells a high continuous uptake into chromatin R N A was observed
to occur throughout interphase, whereas in the normal monkey kidney
cells there was a relatively low uptake in the period before D N A synthesis as compared, in each case, with the uptake during the period of
D N A synthesis. However, it was not possible, with certainty, to associate all the uptake into R N A with net synthesis, because of the existence of turnover of the R N A precursor (see p. 326).
B. C O M P A R I S O N OF C U L T U R E S W I T H G R O W T H IN
VIVO
It was clearly of some interest to extend the measurements of DNA,
total nucleic acid, and dry mass made on cell cultures to the growth of
cells in vivo. Although it was deemed impracticable to film a section of
a tissue in vivo in the same way as had been done in culture, it was
nevertheless thought possible to make useful deductions from the correlation plots of dry mass, total nucleic acid and D N A measured on a
population of individual cell nuclei without having a knowledge of the
cell ages: this approach had already been demonstrated for the measurements on cell cultures (Figs. 4 and 5) to lead to conclusions equivalent
to those ofthe timing measurements (Seed, 1963a).
Such measurements made on smears of normal and tumour-cell
nuclei are shown in Figs. 6 and 7. The smears of normal cells were
prepared from mouse-embryo limb-bud, and the smears of tumour
cells from the growing edge of a spontaneous tumour arising in the
flank of a C + strain mouse.
For the normal embryonic cell nuclei (Fig. 6) there is a similar high
degree of association between D N A and dry mass and between total
nucleic acid and dry mass, in the same way as was obtained for the
freshly prepared monkey kidney cells in culture (Fig. 4) and it would
appear therefore that similar conclusions may be drawn regarding the
coupling of the major parts of the three syntheses. On the other hand,
for the nuclei of spontaneous tumours (Fig. 7) the association between D N A
and dry mass is significantly worse than that between total nucleic
acid and dry mass. It would appear that during the interphase of
the spontaneous tumour cells, the nuclear protein and total nucleic
acid increase approximately together, whereas the nuclear protein and
D N A content increase independently to an appreciable extent. This
result in vivo is therefore similar to that obtained for HeLa (tumour)
cell nuclei in culture.
The above measurements on in vivo systems of animal cells may be
compared with those of McLeish (1960) on plant cell nuclei derived
J. S E E D
consistent with the u.v. photometric measurements (Seed, 1963a). In
HeLa cells a high continuous uptake into chromatin R N A was observed
to occur throughout interphase, whereas in the normal monkey kidney
cells there was a relatively low uptake in the period before D N A synthesis as compared, in each case, with the uptake during the period of
D N A synthesis. However, it was not possible, with certainty, to associate all the uptake into R N A with net synthesis, because of the existence of turnover of the R N A precursor (see p. 326).
B. C O M P A R I S O N OF C U L T U R E S W I T H G R O W T H IN
VIVO
It was clearly of some interest to extend the measurements of DNA,
total nucleic acid, and dry mass made on cell cultures to the growth of
cells in vivo. Although it was deemed impracticable to film a section of
a tissue in vivo in the same way as had been done in culture, it was
nevertheless thought possible to make useful deductions from the correlation plots of dry mass, total nucleic acid and D N A measured on a
population of individual cell nuclei without having a knowledge of the
cell ages: this approach had already been demonstrated for the measurements on cell cultures (Figs. 4 and 5) to lead to conclusions equivalent
to those ofthe timing measurements (Seed, 1963a).
Such measurements made on smears of normal and tumour-cell
nuclei are shown in Figs. 6 and 7. The smears of normal cells were
prepared from mouse-embryo limb-bud, and the smears of tumour
cells from the growing edge of a spontaneous tumour arising in the
flank of a C + strain mouse.
For the normal embryonic cell nuclei (Fig. 6) there is a similar high
degree of association between D N A and dry mass and between total
nucleic acid and dry mass, in the same way as was obtained for the
freshly prepared monkey kidney cells in culture (Fig. 4) and it would
appear therefore that similar conclusions may be drawn regarding the
coupling of the major parts of the three syntheses. On the other hand,
for the nuclei of spontaneous tumours (Fig. 7) the association between D N A
and dry mass is significantly worse than that between total nucleic
acid and dry mass. It would appear that during the interphase of
the spontaneous tumour cells, the nuclear protein and total nucleic
acid increase approximately together, whereas the nuclear protein and
D N A content increase independently to an appreciable extent. This
result in vivo is therefore similar to that obtained for HeLa (tumour)
cell nuclei in culture.
The above measurements on in vivo systems of animal cells may be
compared with those of McLeish (1960) on plant cell nuclei derived