Patterns of Globin Chain Synthesis in Erythroid Colonies Grown from Sheep Marrow of Different Developmental Stages

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Abstract
Erythroid colonies were grown from fetal sheep bone marrow at different stages of development and from adult marrow. Colony numbers increased with erythropoietin concentration, but fetal erythroid cells were more sensitive to the hormone than adult cells. Hb synthesis was characterized in the colonies and compared to that in control marrow incubations. No .beta. chain synthesis was detectable in marrow incubations or erythroid colonies from fetal marrow at 87-96 d [day] gestation. Incubations of 115-120 d marrow showed 5% .beta. chain synthesis while erythroid colonies synthesized up to 20% .beta. chains. Incubations and erythroid colonies from 125 d marrows showed about 27% .beta. chain synthesis, despite a similar increase in colony numbers with erythropoietin as the other marrows. Later in gestation, .beta. chain synthesis was lower in erythroid colonies than in marrow incubations and declined further in erythroid colonies as erythropoietin concentration increased. Adult marrow showed no detectable .gamma. chain synthesis but erythroid colonies produced up to 12% .gamma. chains, the identity of which was confirmed by peptide mapping. All changes in globin synthesis in vitro were correlated with colony numbers. In adult marrow, the maximal level of .gamma. chain production was inversely related to the cloning efficiency of the marrow samples studied. Potential uses of this model for studying globin gene expression are discussed.

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