Aggregation of cells from early chick blastoderms.

The aggregation of dissociated cells from chick blastoderms at Hamburger and Hamilton stages 1-5 was studied. Aggregation was measured during the first 4 h of culture by determination of the proportion of single cells in the medium. No difference in aggregation was found when cells dissociated by either trypsin or EDTA were studied. Similarly the presence or absence of serum in the medium had no appreciable effect on early phases of aggregation, although at 24 h and thereafter, aggregate size was reduced in serum-free cultures. It was found that at all of the stages studied, cells aggregate and sort out into two groups. One group forms a continuous phase of loosely associated cells while the other segregates into several localised areas of closely associated cells within the aggregate. Examination of aggregates up to 7 days in culture showed progressive differentiation within each phase and several identifiable cell types were observed. Basal laminae were present at the boundary between the compact phase and the loose phase.