Arrest of cell division and hemoglobin synthesis in differentiating yolk sac erythroid cells

Abstract

Yolk sac derived erythroid cells of C57B1/Cas fetal mice which are X irradiated with 120 rads at the 10th day of fetal development perform three normal cell cycles and synthesize hemoglobin in a normal fashion until day 12. Between day 12 and 13 normal cells perform one final cell cycle and reduce to half the rate of hemoglobin synthesis per cell; conversely, irradiated erythroid cells do not divide and maintain the full rate of hemoglobin formation. At day 13 irradiated non-divided erythroid cells contain polyribosomes in the same amount and with the same size distribution as normally divided cells and yet synthesize hemoglobin at a two-fold faster rate. This difference of hemoglobin synthesizing capacity is not due to new formation of messenger RNA for hemoglobin, neither it is due to a faster rate of translation, but rather because at day 13 non-divided erythroid cells have maintained the full complement of messenger RNA-ribosomal complexes active for hemoglobin synthesis, while in normally divided erythroid cells the number of messenger RNA-ribosomal complexes active for hemoglobin synthesis is cleaved in the course of cell division. In the irradiated erythroid population the total amount of each globin chain produced in the course of differentiation is not decreased in spite of the arrest of cell division. These data suggest that the total amount of hemoglobin produced during the development of the progeny of a single erythroid cell is programmed in early stages of erythroid differentiation.