TISSUE RECONSTRUCTION FROM DISSOCIATED CELLS 



213 



The general validity of this result was substantiated by extensive 

 observations on a variety of such heterotypic cell combinations. The 

 over-all evidence led to the conclusion that cells in composite aggre- 

 gates went through a process of reshuffling and became sorted out into 

 distinct groupings in accordance with cell-type specificities and func- 

 tional affiliations. However, persuasive as this evidence was, it was in- 

 direct, and its firm acceptance hinged upon further proof of the basic 

 premise: that the cells persisted, indeed, in their original identities 

 throughout dissociation and aggregation; that what appeared to be a 

 result of selective grouping was not actually a site-dependent transfor- 

 mation of cells around centers of morphogenetic influence or dominance. 

 The possibility was not to be disregarded that relatively young embry- 

 onic cells, though presumably determined, might, when removed from 

 the stabilizing effects of their tissue and assimilated in a new frame- 

 work, become diverted in novel directions (Grobstein and Zwilling, 

 1953; Trinkaus, 1956; Moscona, 1957b ) . Needed was a marking system 

 —a means of localizing cells and identifying them as to their origins, not 

 only by their ultimately collective performance but also individually, 

 throughout the course of aggregation and tissue formation. However, 



Figure 11. Section through a L^^. \T. 



group of composite aggre- -^j^ •"• 'vriv.'. 



gates compounded from me- t K' .•■-«■ t ''-ti 



sonephros and cartilage-form- A 



ing cells. Note the central ■ 



core of cartilage and outer 4^ 4 



capsule of nephric epithelium. SSi J 



X-s-r'jff^^' ■■■. 



