Erythroid cell development in fetal mice: Ultrastructural characteristics and hemoglobin synthesis

Abstract

Erythroid cell development in fetal mice, with a total gestation period of 20 to 21 days, occurs, initially, in yolk sac blood islands (8 to 12 days) and, subsequently, in liver (12 to at least 16 days). Erythropoiesis from the eleventh through the fifteenth day of gestation of C57BL/6 J fetal mice was characterized by studies of the ultrastructure and determinations of the types of hemoglobin synthesized by circulating erythroid cells and liver erythroid cells. The circulating nucleated and non-nucleated erythroid cells were separated by centrifugation through silicone fluids. The ultrastructure of the cells was examined by electron microscopy. Hemoglobin types were characterized by electrophoresis in polyacrylamide gel. It is shown that as development of erythroid cells derived from yolk sac blood islands proceeds, the cytoplasmic ribosomes are lost, though the nucleus is retained. At 11 days of gestation these cells actively synthesize hemoglobin, which is predominantly of embryonic types. The capacity to synthesize embryonic hemoglobins is lost as the cytoplasmic ribosomes disappear, which occurs by the fourteenth to fifthteenth day of gestation. By contrast, the development of erythroid cells derived from the liver is characterized by the loss of the nucleus at a stage when the cells retain ribosomes and the capacity to form hemoglobin. The nucleated and non-nucleated erythroid cells derived from hepatic sites of erythropoiesis synthesize predominantly adult-type hemoglobin.