Abstract
Abstract Three embryonic hemoglobins are formed in erythroid cells derived from yolk sac blood islands in fetal mice of the C57BL/6J strain. These cells provide a suitable model to study the rates of synthesis of specific proteins during the differentiation of cells. Erythroid cells differentiate initially in yolk sac blood islands from the 8th to the 10th day of gestation. (Fetal mice have a 20- to 21-day period of gestation.) These cells enter the fetal circulation and continue to develop as a relatively homogeneous population until Day 14 or 15, as indicated by a progressive decrease in the size of the nucleus, increasing pycnosis of nuclear chromatin, increasing content of hemoglobin in the cytoplasm, and decreasing content of ribosomes in the cytoplasm. The relative rates of synthesis of the three embryonic hemoglobins, Hb Ei, Hb Eii, and Hb Eiii, change as these erythroid cells differentiate. The synthesis of Hb Ei, the most abundant of the hemoglobins present at Day 10, decreases markedly after Day 11, while the synthesis of Hb Eii proceeds at a relatively linear rate over the entire period and by Day 12 is present in the largest amount. Hb Eiii is formed at a slower rate than Hb Ei or Hb Eii during the entire period from Day 10 to Day 14. Hemoglobin formation in yolk sac erythroid cells is not inhibited by actinomycin D from Day 10, while the antibiotic does inhibit RNA formation and non-heme protein synthesis in these cells. It is suggested that changes in rates of synthesis of the three embryonic hemoglobins which occur as yolk sac erythroid cells develop between Days 10 and 14 may be largely determined by factors regulating protein formation which do not require the immediate or continued synthesis of RNA.
Highlights
Since column chromatography was not suitable for analysis of multiple fetal mouse blood samples required in this study, the correspondence between the four hemoglobins separated by electrophoresis (Fig. 1) and the four hemoglobins separated by carboxymethyl cellulose column chromatography in our previous studies (I) was determined
Twelve-day fetal mouse yolk sac erythroid cells were labeled with 14C-valine, or 14C-lysine and 3Harginine, lysates were prepared from these cells, and hemoglobins in these lysates were separated by electrophoresis in polyacrylamide gel
This paper provides evidence pertinent to the question of whether, in a single population of erythroid cells which form three distinct types of hemoglobins, the relative rates of synthesis of these proteins change as the cells differentiate
Summary
Animals-Threeto four-week-old female mice of C57BL/6J inbred strain, and two- to five-month-old males of the same strain were purchased from the Jackson Laboratory, Bar Harbor, Maine. The method for obtaining dated fetal development was based on timed matings of hormonally primed immature females [13]. The 1st day of gestation was counted as the morning following mating. Preparation of Erythroid Cells-At the 10th day of gestation, erythroid cells were prepared from the peripheral blood of fetuses as follows. The pregnant uteri were removed and placed in a. 1:l mixture of Tyrode’s solution and y-globulin-free fetal calf serum (Solution A).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
