490
A . A . MOSCONA
I I . A G G R E G A T I O N OF C E L L S
A. G E N E R A L
Procedures for the dissociation of embryonic tissues into suspensions
of viable cells, with particular reference to the use of such
cell suspensions in developmental studies, have been described and
discussed in Chapter 2, p. 49. W e may continue here with the
general statement that freshly dissociated embryonic cells from various
avian and mammalian tissues or organ rudiments display, under
suitable in vitro conditions, a striking tendency to aggregate and to
restitute histotypic systems. This propensity varies in degree according
to the type and origin of the cells, their state of development, and
the environmental conditions to which they are exposed. Studies
on various cellular and environmental aspects of aggregation might
the cell that affect the construction of cellular groupings, formation of
histogenetic pattern and differentiation. The purpose of this article is to
take stock of some of the more recent information relevant to this topic
within a convenient framework of related problems. The emphasis is
more on factual aspects than on theoretical or speculative considerations. I have not attempted to list exhaustively all data and views that
could be of interest since many of these have been quite recently presented elsewhere (P. Weiss, 1958, 1961; Abercrombie, 1958, 1961;
Willmer, 1960, 1961; L. Weiss, 1960; Moscona, 1962b, c) or can be
found in other chapters of this volume.
Since this survey is concerned exclusively with work on higher vertebrate (avian and mammalian) cells, it should be recalled that the
phenomenon of cell aggregation was first discovered in experiments
with separated amphibian and sea-urchin blastomeres (Roux, 1894;
Herbst, 1900) and marine sponge cells (Wilson, 1908), and that it was
widely employed by Holtfreter (1943, 1948) in his classical studies on
amphibian gastrulation; it is also a normal feature in the life cycle of
various micro-organisms, particularly the slime moulds (Raper and
Thorn, 1941; Bonner, 1952; Sussman and Sussman, 1956; Shaffer,
1956; Gregg, 1960; Gerisch, 1960). It should also be stressed that,
although cell aggregation is treated here as an experimental discipline
for studying cellular dynamics under relatively simplified conditions it
represents, in several fundamental respects, a counterpart ofthe normal
processes of dissociation, dispersal, aggregation, and grouping of cells
that occur continuously in prenatal and postnatal development, as well
as in wound healing, regeneration, and various pathological processes.
A . A . MOSCONA
I I . A G G R E G A T I O N OF C E L L S
A. G E N E R A L
Procedures for the dissociation of embryonic tissues into suspensions
of viable cells, with particular reference to the use of such
cell suspensions in developmental studies, have been described and
discussed in Chapter 2, p. 49. W e may continue here with the
general statement that freshly dissociated embryonic cells from various
avian and mammalian tissues or organ rudiments display, under
suitable in vitro conditions, a striking tendency to aggregate and to
restitute histotypic systems. This propensity varies in degree according
to the type and origin of the cells, their state of development, and
the environmental conditions to which they are exposed. Studies
on various cellular and environmental aspects of aggregation might
the cell that affect the construction of cellular groupings, formation of
histogenetic pattern and differentiation. The purpose of this article is to
take stock of some of the more recent information relevant to this topic
within a convenient framework of related problems. The emphasis is
more on factual aspects than on theoretical or speculative considerations. I have not attempted to list exhaustively all data and views that
could be of interest since many of these have been quite recently presented elsewhere (P. Weiss, 1958, 1961; Abercrombie, 1958, 1961;
Willmer, 1960, 1961; L. Weiss, 1960; Moscona, 1962b, c) or can be
found in other chapters of this volume.
Since this survey is concerned exclusively with work on higher vertebrate (avian and mammalian) cells, it should be recalled that the
phenomenon of cell aggregation was first discovered in experiments
with separated amphibian and sea-urchin blastomeres (Roux, 1894;
Herbst, 1900) and marine sponge cells (Wilson, 1908), and that it was
widely employed by Holtfreter (1943, 1948) in his classical studies on
amphibian gastrulation; it is also a normal feature in the life cycle of
various micro-organisms, particularly the slime moulds (Raper and
Thorn, 1941; Bonner, 1952; Sussman and Sussman, 1956; Shaffer,
1956; Gregg, 1960; Gerisch, 1960). It should also be stressed that,
although cell aggregation is treated here as an experimental discipline
for studying cellular dynamics under relatively simplified conditions it
represents, in several fundamental respects, a counterpart ofthe normal
processes of dissociation, dispersal, aggregation, and grouping of cells
that occur continuously in prenatal and postnatal development, as well
as in wound healing, regeneration, and various pathological processes.