Erythroid cell-development in fetal mice: synthetic capacity for different proteins.

Abstract

Abstract Fetal mice of the C57BL/6J strain were used in a study of the rates of synthesis of RNA, total protein and hemoglobin by developing erythroid cells derived from two different sites of erythropoiesis, namely, yolk-sac blood islands and liver. In fetal mice, erythropoiesis proceeds initially in yolk-sac blood islands (8 to 12 days of gestation) and, subsequently, in liver (12 to at least 16 days). In yolk-sac erythroid cells, RNA content and RNA synthesis decrease markedly between the eleventh and thirteenth days of gestation. The rate of synthesis of non-heme protein in these cells declines rapidly from day 12 to 13, while the rate of hemoglobin formation remains essentially unchanged from day 11 through day 13. Actinomycin D inhibits the synthesis of RNA and non-heme protein, but not hemoglobin formation by yolk-sac erythroid cells of the 11-day fetus. In erythroid cells developing in liver, the rate of hemoglobin synthesis, averaged per cell, remains essentially unchanged between day 13 and 15. The rate of hemoglobin synthesis in circulating non-nucleated liver-derived erythroid cells is about threefold that in the population of nucleated erythroid cell precursors in the liver. Actinomycin inhibits hemoglobin synthesis by liver erythroid cells prepared from the liver of the 13-day fetus but not from 14-, 15- or 16-day fetuses. These data suggest that in yolk-sac erythroid cells, non-heme protein formation is limited by a relatively short-lived component essential to protein synthesis, which may be messenger RNA. Hemoglobin formation in yolk-sac erythroid cells after day 11 and in liver erythroid cells after day 14 appears to proceed without a dependence on new RNA synthesis.