Control of Hemoglobin Synthesis in the Cultured Chick Blastoderm

Richard D Levere,S Granick

doi:10.1016/s0021-9258(18)96086-2

Abstract

Abstract The early, de-embryonated chick blastoderm, cultured in vitro, closely simulates a phased culture of erythroid cells. This fact permits the study of hemoglobin synthesis from colorless erythroblast precursor cells to fully hemoglobinated erythrocytes. When δ-aminolevulinic acid is added to colorless blastoderms, thereby by-passing δ-aminolevulinic acid synthetase, copious amounts of porphyrins, and presumably of heme, are formed. This result indicates that in the erythroid precursor cells of the early blastoderms heme synthesis is limited by the activity of δ-aminolevulinic acid synthetase. The addition of δ-aminolevulinate also results in an increase in globin synthesis and hemoglobin formation. The enhancing effect of δ-aminolevulinic acid on hemoglobin formation is not abolished by actinomycin D but is prevented by puromycin. This result suggests that δ-aminolevulinic acid forms heme which stimulates globin synthesis at the ribosome level. It is conjectured that heme may be necessary for the appropriate folding of the globin polypeptide in the completion of its synthesis. The hypothesis is proposed that the formation of δ-aminovulinic acid synthetase, which is under repressor control, is the limiting and controlling reaction in the formation of hemoglobin. Such a hypothesis would explain the fact that no free globin is formed and that monomeric globin and heme are formed in a 1:1 ratio.

Highlights

SUMMARYThe early, de-embryonated chick blastoderm, cultured in vitro, closely simulates a phased culture of erythroid cells
This fact permits the study of hemoglobin synthesis from colorless erythroblast precursor cells to fully hemoglobinated erythrocytes
These results indicate that all of the enzymes of the heme biosynthetic chain exclusive of the first one, Le

Summary

SUMMARY

The early, de-embryonated chick blastoderm, cultured in vitro, closely simulates a phased culture of erythroid cells. The hematopoietic tissue of the early blastoderm starts with colorless cells at a stage prior to initiation of hemoglobin synthesis and these differentiate in 24 to 48 hours into fully developed erythrocytes This tissue may be regarded as a phased culture of erythroid cells and its differentiation studied with respect to time. O’Brien [5] has shown that when young blastoderms, i.e. prior to the fifth to sixth somite stage, are de-embryonated and grown on a simple glucose agar medium there is inhibition of cell migration and maturation in all cells except the developing hematopoietic mesoderm This hematopoietic mesoderm is arranged in clusters of syncytial tissue called blood islands, and is found in the horseshoe-shaped area where hemoglobin will eventually appear.

UROGENASE

AND METHODS

and Methods”

Average

Somite tive streak

DISCUSSION