Abstract
1. 1. This report examines the possibility of compounding cells in suspension into histoformative aggregates, under controllable, replicable and potentially quantitative conditions. 2. 2. A cell aggregation procedure based on readily standardizable manipulations is described, whereby cells dissociated enzymatically from embryonic tissues may be aggregated in various combinations and concentrations into developmentally effective multicellular structures; it is suitable for analyzing mutual reactions of cells and their responses to diverse environmental conditions. 3. 3. The characteristics of aggregates produced by cells of different types or origins varied markedly under otherwise identical conditions. The number, size distribution, shape and internal structure of aggregates formed in 24 hours by cells of a given type or by a cell population of a known composition was termed the aggregation pattern of the cells in testing (cell type-dependent aggregation pattern) for the specified set of conditions. 4. 4. Aggregation patterns of the two types of cells studied were not noticeably affected by gross variations in cell concentrations. It is suggested that they represent a typical, reproducible and measurable expression of cell behavior, providing useful “baselines” for further analysis. For comparative purposes, they may be conveniently expressed as the ratio between average diameter and number of aggregates, which provides an index of aggregation for the given culture and conditions. 5. 5. The histoformative effectiveness of this procedure was established by studying the differentiation of aggregates. In all experiments the re-assembled cells resumed development in accordance with their pre-established directions. 6. 6. Type-specific grouping of cells in heterotypic cell aggregates, compounded by the present procedure, was examined in combinations of embryonic chick and mouse cells. In spite of their initial random bunching and irrespective of species origin, the aggregated cells became sorted out and associated in accordance with their histogenetic identities and compatibilities, thus confirming prior findings on “self-assembled” aggregates. 7. 7. The size distribution of aggregates could be effectively controlled by varying the frequency of rotation of cultures. The possibility of a measurable relationship between the forces applied to cells and cell cohesiveness is discussed. 8. 8. The rate and effectiveness of aggregation processes in this system was found to decrease at suboptimal temperatures. At 15 °C, the two types of cells examined showed no aggregation; transferred to 38 °, these cells aggregated readily. The possibility is considered that normal bonding and formative association of cells depend on thermo-sensitive synthetic activities, related, perhaps, to elaboration of surface products, and that their rate is slowed down or otherwise modified at suboptimal temperatures.
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