4. CELL T Y P E S
155
has been shown to depend on the Ca++ content of the medium (Fig. 4 ) ;
these cells when growing in a normal calcium-containing medium are
round and become spindle-shaped when the C a
++ is reduced, though
the growth rates in the two media are much the same (Owens, 1957).
Removal of divalent ions by the chelating agent E D T A (Versene)
causes blebs to emerge from the surface of cells, an action which is
reversible on adding C a
++ ions (Dornfeld and Owczarzak, 1957).
Remarkable outgrowths and nerve-like processes can be caused to
form on the surfaces of rat fibroblasts in vitro by the application of
ribosenucleoproteins obtained from the ribosomes from the liver
(Murray, 1957) (Fig. 5). L-Strain cells in suspension cultures in synthetic medium 199 under certain conditions attach themselves together
as sheets of cells, while the addition of serum or of methyl cellulose to
the 199 causes them to remain in suspension as separate cells (Kuchler,
Marlowe and Merchant, 1960).
A realization of the reactivity and variability of the surfaces of cells
and their organelles is certainly one of the conspicuous fruits of the
Tissue Culture method. Events of a more subtle kind, but of the same
sort, are seen when cultures of kidney or salivary-gland epithelia are
grown on one side of a millipore filter and cultures of spinal cord or of
the appropriate mesenchyme are planted on the other. The epithelial
cells then change from flat, rather amorphous cells, to columnar cells
arranged in definite tubules (see p. 479). This is thought to be due to
chemical factors emanating from the "inducing tissues" and penetrating
through the millipore filter. Presumably the many other examples of
epithelial differentiation being dependent on the underlying mesenchyme cells are explicable on similar lines.
It is clear, from what has been said so far, that cells can alter their
form to a remarkable extent in culture, and that both internal and
external factors are at work. It is true that the HeLa cell is an abnormal
and peculiarly resistant type of cell, but nevertheless its morphological
versatility, even under similar external conditions, in culture (see p. 149)
must be regarded as a cautionary tale.
Diagnosis of the class to which a cell belongs by the shape of the cell
alone is thus precarious, if not impossible. Moreover, cells in all the
classes so far mentioned (e.g. epitheliocytes, mechanocytes, amoebocytes etc.) are liable to have their shapes and movements modified to
a greater or less extent by such external factors as have already been
discussed and probably by many others besides, and in order to group
cells into these classes with certainty it is necessary to have much more
information about them than can be gleaned from studying only their
outward form.
155
has been shown to depend on the Ca++ content of the medium (Fig. 4 ) ;
these cells when growing in a normal calcium-containing medium are
round and become spindle-shaped when the C a
++ is reduced, though
the growth rates in the two media are much the same (Owens, 1957).
Removal of divalent ions by the chelating agent E D T A (Versene)
causes blebs to emerge from the surface of cells, an action which is
reversible on adding C a
++ ions (Dornfeld and Owczarzak, 1957).
Remarkable outgrowths and nerve-like processes can be caused to
form on the surfaces of rat fibroblasts in vitro by the application of
ribosenucleoproteins obtained from the ribosomes from the liver
(Murray, 1957) (Fig. 5). L-Strain cells in suspension cultures in synthetic medium 199 under certain conditions attach themselves together
as sheets of cells, while the addition of serum or of methyl cellulose to
the 199 causes them to remain in suspension as separate cells (Kuchler,
Marlowe and Merchant, 1960).
A realization of the reactivity and variability of the surfaces of cells
and their organelles is certainly one of the conspicuous fruits of the
Tissue Culture method. Events of a more subtle kind, but of the same
sort, are seen when cultures of kidney or salivary-gland epithelia are
grown on one side of a millipore filter and cultures of spinal cord or of
the appropriate mesenchyme are planted on the other. The epithelial
cells then change from flat, rather amorphous cells, to columnar cells
arranged in definite tubules (see p. 479). This is thought to be due to
chemical factors emanating from the "inducing tissues" and penetrating
through the millipore filter. Presumably the many other examples of
epithelial differentiation being dependent on the underlying mesenchyme cells are explicable on similar lines.
It is clear, from what has been said so far, that cells can alter their
form to a remarkable extent in culture, and that both internal and
external factors are at work. It is true that the HeLa cell is an abnormal
and peculiarly resistant type of cell, but nevertheless its morphological
versatility, even under similar external conditions, in culture (see p. 149)
must be regarded as a cautionary tale.
Diagnosis of the class to which a cell belongs by the shape of the cell
alone is thus precarious, if not impossible. Moreover, cells in all the
classes so far mentioned (e.g. epitheliocytes, mechanocytes, amoebocytes etc.) are liable to have their shapes and movements modified to
a greater or less extent by such external factors as have already been
discussed and probably by many others besides, and in order to group
cells into these classes with certainty it is necessary to have much more
information about them than can be gleaned from studying only their
outward form.