8 



Microenvironmental 



Influences in 



Cytodifferentiation 



Clifford Grohstein 



Department of Biological Sciences 

 Stanford University, Stanford, California 



My objective is to present some facts which suggest that the materials 

 between, and normally closely associated with, the surfaces of cells 

 may be important in controlling cytodifferentiative behavior. Since 

 cytodifferentiation and organismal diversification are opposite faces 

 of the developmental coin, controls for the one must underlie the 

 regularities of the other. There is a large bodv of information indicat- 

 ing that cytodifferentiation is sensitive to extrinsic influence. How- 

 ever, my emphasis here is not on extrinsic factors generally, but on 

 those which reside in the immediate vicinity of the cell, in the large- 

 molecular materials which are produced by the cell or its close neigh- 

 bors and which may continuously interact with their source subse- 

 quent to production, ft is in these terms that I define what is referred 

 to in this discussion as the microenvironment. 



I shall limit myself to consideration of two of the several available 



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