68
A . M O S C O N A , O. A . T R O W E L L A N D E . N. W I L L M E R
of the foundation member of a clone is necessarily a matter of some
uncertainty except in a few rather exceptional instances.
The primary object of making clones of cells is to obtain a completely
uniform population of cells, which would normally be impossible by
the more usual culture methods. For some purposes the achievement
of this object is very desirable and indeed necessary, but, for others, the
method should be considered more critically. If it is important to know
the nature of the cell, and if that cell is to be considered as carrying on
its normal function while growing as a clone, then the method is very
suspect. On the other hand, for many studies on growth, on synthesis
of DNA, and on general cellular nutrition and metabolism, cultures
made from cell suspensions and clones can be of the greatest value,
though the results should in the first instance not be used as a base
from which to generalize, as they may be quite inapplicable to cells
of other strains or even to the same cells grown under other conditions.
Clones which have been divided and then cultured in different
laboratories certainly become different, though the reasons for these
differences are not yet fully understood. There is, of course, plenty
of opportunity in such cultures both for the occurrence of mutations
and for the subsequent selection of these. Chromosome abnormalities
and irregular mitoses are of frequent occurrence in cells in tissue and
cell cultures (Hsu and Pomerat, 1953b; Levan, 1956; Chu, Sanford and
Earle, 1958; Chu and Giles, 1959), particularly in those which are
growing most rapidly and in cultures which have been subjected to
abnormal temperature fluctuations (Stilwell, 1944, 1948), and to heterologous tissue extracts (Frederic and Corin, 1962).
2. Suspension Cultures
When suspensions of cells are made by any of the various methods
used for cell isolation they may subsequently be treated in several
different ways.
They may simply be allowed to settle down, as already described,
on the bottoms of flat flasks, dishes or Roux bottles, etc. from which,
after a period of growth, they may be removed and resuspended either
mechanically or by treatment with trypsin as before. They may then
be analysed or subcultured as required. In these cultures the cells are
fixed to the surface of the vessel and the fluid is relatively stagnant.
Second, they may be allowed to settle in roller tubes and then
treated like ordinary roller-tube cultures. In this method the cells
are fixed, but the fluid is in constant movement and thus the amount of
medium and the speed of rotation of the tubes are both important
(Earle, Schilling and Bryant, 1954).
Third, in contrast to the experience of the early tissue culturists,
A . M O S C O N A , O. A . T R O W E L L A N D E . N. W I L L M E R
of the foundation member of a clone is necessarily a matter of some
uncertainty except in a few rather exceptional instances.
The primary object of making clones of cells is to obtain a completely
uniform population of cells, which would normally be impossible by
the more usual culture methods. For some purposes the achievement
of this object is very desirable and indeed necessary, but, for others, the
method should be considered more critically. If it is important to know
the nature of the cell, and if that cell is to be considered as carrying on
its normal function while growing as a clone, then the method is very
suspect. On the other hand, for many studies on growth, on synthesis
of DNA, and on general cellular nutrition and metabolism, cultures
made from cell suspensions and clones can be of the greatest value,
though the results should in the first instance not be used as a base
from which to generalize, as they may be quite inapplicable to cells
of other strains or even to the same cells grown under other conditions.
Clones which have been divided and then cultured in different
laboratories certainly become different, though the reasons for these
differences are not yet fully understood. There is, of course, plenty
of opportunity in such cultures both for the occurrence of mutations
and for the subsequent selection of these. Chromosome abnormalities
and irregular mitoses are of frequent occurrence in cells in tissue and
cell cultures (Hsu and Pomerat, 1953b; Levan, 1956; Chu, Sanford and
Earle, 1958; Chu and Giles, 1959), particularly in those which are
growing most rapidly and in cultures which have been subjected to
abnormal temperature fluctuations (Stilwell, 1944, 1948), and to heterologous tissue extracts (Frederic and Corin, 1962).
2. Suspension Cultures
When suspensions of cells are made by any of the various methods
used for cell isolation they may subsequently be treated in several
different ways.
They may simply be allowed to settle down, as already described,
on the bottoms of flat flasks, dishes or Roux bottles, etc. from which,
after a period of growth, they may be removed and resuspended either
mechanically or by treatment with trypsin as before. They may then
be analysed or subcultured as required. In these cultures the cells are
fixed to the surface of the vessel and the fluid is relatively stagnant.
Second, they may be allowed to settle in roller tubes and then
treated like ordinary roller-tube cultures. In this method the cells
are fixed, but the fluid is in constant movement and thus the amount of
medium and the speed of rotation of the tubes are both important
(Earle, Schilling and Bryant, 1954).
Third, in contrast to the experience of the early tissue culturists,