TISSUE RECONSTRUCTION FROM DISSOCIATED CELLS 203 



limb-buds aggregated into numerous regular spheroids (see Figure 

 4 ) . Thus, in spite of the identity in environmental conditions and of the 

 mechanical forces acting upon the cells, each type of cells or each cell 

 population displayed diagnostically distinct grouping properties and 

 patterns of association. 



The interest in these difiFerential aggregation patterns and their 

 significance was considerably amplified by the finding that their major 

 features were remarkably little affected by gross differences in cell con- 

 centration (Moscona, 1961). For instance, the average diameter of 

 retina cell aggregates was not appreciably altered across a concentra- 

 tion range from six million to 60,000 cells per three ml. of culture 

 medium; the total number of aggregates fell, of course, accordingly 

 (Figure 5). In the case of liver cells, which under the observed con- 

 ditions aggregated into a single cluster per culture, the aggregate di- 

 ameter decreased relative to the fall in cell concentration, but its typical 

 shape was not altered. 



Of equal interest was the finding that the major featiires of aggre- 

 gation patterns were not narrowly species-specific, i.e., that embryonic 

 mouse cells and embrvonic chick cells' if derived from similar tissues 

 at a comparable stage of development, produced strikingly similar 



Number of aggregates per culture 

 mm 33 19 9 11 7 



^ 1 +■ 



• ••• 



• •.' • •• 



03 

 Oi 



re 

 u 



re 



0.5- - 



••• 



1 



12 4 6 8 10 



Dilution factor 



Figure 5. Cell concentration and size distribution of aggregates: neural-retina cells, 7- 

 day chick embryo. All cultures in a standard medium, 70 r.p.m., at 38° C. for 24 hours. 



