THE RELATIONSHIP BETWEEN CELL MATURATION and PROLIFERATION IN the ERYTHROID SYSTEM of the RAT

Calculations have been made of the change with time in the tritiated thymidine labelling index of erythroid cells in normal and anaemic rats, on the basis of two different models of the erythroid system. In the first model it is assumed that cells pass from one stage of maturation to the next at all phases of the cell cycle, whereas in the second model the cells can only progress to the next stage when they reach a certain point in the cell cycle. the changes in labelling index predicted on the basis of these two models are markedly different, especially in the non-dividing stages of the system, and the change in labelling index as a function of time therefore provides an experimental method for distinguishing between the two models. the experimental data favours the model in which cells cross compartmental boundaries at all stages of maturation. Some important consequences of this model are discussed.