Generation-dependent control mechanisms in cell proliferation and differentiation--the power of two

There is evidence that the proliferation of cells is controlled by the number of divisions after leaving a multi-potent (stem) cell. A detailed study of the growth of tissue in the small intestinal tract, more precisely the growth of crypts and villi, suggests that not only the proliferation but also the differentiation of cells obey the same biological law. We postulate a theory of a cellular internal control mechanism: the cell-generation control of differentiation and proliferation. This basic mechanism, together with external influences, determines the kinetic behaviour of the crypt-villus system.