516
A. A. MOSCONA
C. DEVELOPMENT IN HETEROTYPIC CELL AGGREGATES
Heterotypic aggregates are compounded of cells derived from two or
more different tissues or organs and intermingled in suspension. The
cells may be from the same or from different species, from embryos in
similar or in different stages of development. The cells may be combined
in equal or different proportions; the combinations may include
neoplastic cells. Self-aggregation, centrifugation, and aggregation by
rotation have been used. Heterotypic cell aggregates have been employed in studies on the stability of histotypic traits in dissociated cells,
sorting out, regional grouping of cells in aggregates, and inductive
interactions. Theoretically, aggregates compounded of cells from
different tissues could show one of three results: the intermingled cells
might not become organized into recognizable structures; one of the
cell populations or cell types might predominate, inhibiting the other,
or imposing its developmental pattern on the rest; or, thirdly, the cells
might become sorted out in accordance with their type-specificities,
derivations, and functional identities. The available evidence supports
the third possibility, without altogether excluding the others.
Occurrence of sorting out and selective grouping of commingled
heterotypic cells was inferred from the histology of aggregates compounded from mixed suspensions of limb-bud and mesonephric cells
from 3-5 day chick embryos (Trinkaus and Groves, 1955; Moscona,
1956); in the composite aggregates, distinct areas of cartilage, cutaneous
of biosynthetic capacities, absence from the environment of necessary
precursors or co-factors, or the fact that cellular organization and
interaction are essential to specialized functions" (Eagle, 1959). That
the changes need not be irreversible was seen in monolayer-modified
skin cells which, when co-aggregated with freshly dissociated skin cells,
"reverted" to synthesizing keratin (Moscona, 1960). It is not known
whether this reversion was mediated by the dermal or epidermal cells
in the freshly dissociated material; co-aggregation with skeletogenic
mesenchyme cells did not cause differentiation of monolayer-modified
skin cells. It is possible that cultures of skin cells present in this respect a
special case; one may assume, in analogy with the process of wound
healing, that cells derived from the basal layer retain, at least for a time,
their developmental properties and can display them under suitable
conditions of aggregation. It would be rash, however, to speculate
further in the absence of more complete information on changes in
developmental and biosynthetic properties of embryonic cells grown in
monolayer.
A. A. MOSCONA
C. DEVELOPMENT IN HETEROTYPIC CELL AGGREGATES
Heterotypic aggregates are compounded of cells derived from two or
more different tissues or organs and intermingled in suspension. The
cells may be from the same or from different species, from embryos in
similar or in different stages of development. The cells may be combined
in equal or different proportions; the combinations may include
neoplastic cells. Self-aggregation, centrifugation, and aggregation by
rotation have been used. Heterotypic cell aggregates have been employed in studies on the stability of histotypic traits in dissociated cells,
sorting out, regional grouping of cells in aggregates, and inductive
interactions. Theoretically, aggregates compounded of cells from
different tissues could show one of three results: the intermingled cells
might not become organized into recognizable structures; one of the
cell populations or cell types might predominate, inhibiting the other,
or imposing its developmental pattern on the rest; or, thirdly, the cells
might become sorted out in accordance with their type-specificities,
derivations, and functional identities. The available evidence supports
the third possibility, without altogether excluding the others.
Occurrence of sorting out and selective grouping of commingled
heterotypic cells was inferred from the histology of aggregates compounded from mixed suspensions of limb-bud and mesonephric cells
from 3-5 day chick embryos (Trinkaus and Groves, 1955; Moscona,
1956); in the composite aggregates, distinct areas of cartilage, cutaneous
of biosynthetic capacities, absence from the environment of necessary
precursors or co-factors, or the fact that cellular organization and
interaction are essential to specialized functions" (Eagle, 1959). That
the changes need not be irreversible was seen in monolayer-modified
skin cells which, when co-aggregated with freshly dissociated skin cells,
"reverted" to synthesizing keratin (Moscona, 1960). It is not known
whether this reversion was mediated by the dermal or epidermal cells
in the freshly dissociated material; co-aggregation with skeletogenic
mesenchyme cells did not cause differentiation of monolayer-modified
skin cells. It is possible that cultures of skin cells present in this respect a
special case; one may assume, in analogy with the process of wound
healing, that cells derived from the basal layer retain, at least for a time,
their developmental properties and can display them under suitable
conditions of aggregation. It would be rash, however, to speculate
further in the absence of more complete information on changes in
developmental and biosynthetic properties of embryonic cells grown in
monolayer.