14. CELL AGGREGATES
501
neural retina and other trypsin-dissociated cells may therefore be due
to a functional impairment of polysaccharide-containing products of
the cell surface involved in cell-binding. Similarly, the interference of
D-glucosamine with cell aggregation (Garber, 1962, 1963) could be due
to direct or indirect blocking of cell surface groupings prerequisite for
normal attachment of cells. Cell-type-specific inhibition of aggregation
is caused by heat-inactivated serum from rabbits immunized with dissociated cells (Moscona and Moscona, 1962); thus, in anti-serum
against liver cells, freshly dissociated liver cells remain dispersed while
retina cells aggregate normally. Inhibited liver cells, when washed and
resuspended in normal medium, aggregate. O f particular interest with
respect to the mechanism of cell binding, are the findings (Moscona and
Moscona, 1963) that inhibition of protein synthesis at the R N A level by
puromycin blocks, reversibly, the capacity of dissociated cells for
mutual reattachment and aggregation. Actinomycin D which interferes
with protein synthesis by suppressing R N A - D N A polymerase also
inhibits cell aggregation. Some protein synthesis appears thus to be
essential for the reattachment and aggregation of cells. An evaluation of
these and related effects on the mechanism of cell contact is beyond the
task of this article; they are mentioned here primarily to illustrate
the type of studies to which aggregation of dissociated cells by rotation
lends itself effectively.
E. CELLULAR FACTORS IN
ROTATION-MEDIATED AGGREGATION
O f the factors that affect aggregation of dissociated cells, the origin,
developmental state, and population composition of the suspension are
of obvious significance. Cells from different tissues ofthe same embryo
differ in their manner and result of aggregation and form distinct cellor tissue-specific aggregation patterns which reflect the cumulative
properties of the cell population under test (Moscona, 1961a, c) (Fig.
2 a-d). The features ofthe pattern (shape, size distribution, number,
and internal structure of aggregates) vary for cells from the same tissue
in different states of development. (Moscona 1962 c ; Kuroda, 1963).
However, under a uniform set of conditions such patterns are remarkably consistent and reproducible; furthermore, they change
little across a wide range of cell concentrations, provided that the
relative proportions of various cell types in the population are retained.
The external features of aggregates are usually stabilized in 24 h, in that
no further major changes in number, size distribution or general shape
of aggregates occur thereafter; subsequent increase in size of or changes
in shape of aggregates are due to growth, and only rarely to attach-
501
neural retina and other trypsin-dissociated cells may therefore be due
to a functional impairment of polysaccharide-containing products of
the cell surface involved in cell-binding. Similarly, the interference of
D-glucosamine with cell aggregation (Garber, 1962, 1963) could be due
to direct or indirect blocking of cell surface groupings prerequisite for
normal attachment of cells. Cell-type-specific inhibition of aggregation
is caused by heat-inactivated serum from rabbits immunized with dissociated cells (Moscona and Moscona, 1962); thus, in anti-serum
against liver cells, freshly dissociated liver cells remain dispersed while
retina cells aggregate normally. Inhibited liver cells, when washed and
resuspended in normal medium, aggregate. O f particular interest with
respect to the mechanism of cell binding, are the findings (Moscona and
Moscona, 1963) that inhibition of protein synthesis at the R N A level by
puromycin blocks, reversibly, the capacity of dissociated cells for
mutual reattachment and aggregation. Actinomycin D which interferes
with protein synthesis by suppressing R N A - D N A polymerase also
inhibits cell aggregation. Some protein synthesis appears thus to be
essential for the reattachment and aggregation of cells. An evaluation of
these and related effects on the mechanism of cell contact is beyond the
task of this article; they are mentioned here primarily to illustrate
the type of studies to which aggregation of dissociated cells by rotation
lends itself effectively.
E. CELLULAR FACTORS IN
ROTATION-MEDIATED AGGREGATION
O f the factors that affect aggregation of dissociated cells, the origin,
developmental state, and population composition of the suspension are
of obvious significance. Cells from different tissues ofthe same embryo
differ in their manner and result of aggregation and form distinct cellor tissue-specific aggregation patterns which reflect the cumulative
properties of the cell population under test (Moscona, 1961a, c) (Fig.
2 a-d). The features ofthe pattern (shape, size distribution, number,
and internal structure of aggregates) vary for cells from the same tissue
in different states of development. (Moscona 1962 c ; Kuroda, 1963).
However, under a uniform set of conditions such patterns are remarkably consistent and reproducible; furthermore, they change
little across a wide range of cell concentrations, provided that the
relative proportions of various cell types in the population are retained.
The external features of aggregates are usually stabilized in 24 h, in that
no further major changes in number, size distribution or general shape
of aggregates occur thereafter; subsequent increase in size of or changes
in shape of aggregates are due to growth, and only rarely to attach-