What We Do Not Know About Differentiation

The outstanding recent advances in the analysis of differentiation are in concept and method. In this paper examples are provided to demonstrate that formulation of the problem of differentiation in terms of biosynthesis and its control poses questions in new and more manageable ways. As examples, reference will be made to: (1) the question of control of the sets of specialized properties by which we define a cell type; (2) propagability of differentiated states; (3) developmental bias in relation to intracellular events; and (4) the mechanisms of extrinsic control of differentiation. Particular attention, also, will be focused on the relationship of morphogenetic to biosynthetic events.