The anemia-induced switch from hemo. In eukaryotes, the molecular mechanisms involved in gene activation and in the subsequent production of specific cell proteins are largely unknown. To study gene activation in mammals, a cell population is needed that can be stimulated to transcribe the messenger RNA for a particular protein in response to a defined stimulus. We have studied the erythropoietin-dependent synthesis of hemoglobin C (HbC) in goat (and sheep) bone-marrow cultures for this purpose. Erythropoietin, a glycoprotein hormone, appears to stimulate precursor blood cells in the bone marrow to differentiate into cells that produce hemoglobin (1-3). The type of hemoglobin produced by these cells is determined by the genetic makeup of the animal and by its stage of development. For example, sheep and goats homozygous for hemoglobin A (HbA) pass through a series of developmental stages during which they produce HbF (a2Y2), then HbC (aZ2c), andfinally-the adult HbA (aZ82A) (4-9). However, in response to severe anemia, an adult goat making HbA completely switches from the synthesis of HbA to HbC (4). There is a lag of 3 days between the induction of anemia and the detection of Oc globin synthesis in the marrow (10), suggesting that flc globin is produced by a newly stimulated population of precursor cells. As the anemia is relieved, HbA again is synthesized. The switch from MA to tic synthesis can be elicited in normal, nonanemic animals by injection of partially purified erythropoietin preparations (10-13).We have shown (14) that sheep and goats that are synthesizing HbA have only the mRNA for MA (and a) globin in their erythroid cells, while animals synthesizing HbC have only the mRNA for flc (and a)
METHODSSource and Preparation of Cells. Goats used in this study were over 6 months old and had only HbA detectable in their peripheral blood, as determined by thin-layer electrophoresis on cellulose acetate (14). The animals were anesthesized by intravenous injection of sodium pentobarbital (60 mg/ml, 0.5 ml/kg) and exsanguinated through a femoral artery. The femurs and humeri were removed, their proximal and distal ends were cut off to expose the marrow cavity, and the marrow was extruded by flushing medium (Eagle's minimum essential medium for suspension culture; Microbiological Associates, Bethesda, Md.) through the bones. The cells were separated by being expelled from a 50-ml syringe through a. 20-gauge needle, were washed once with Eagle's medium, and then were resuspended in NCTC-109 medium (Microbiological Assoc.) and disaggregated by expulsion through 'successively smaller-bore syringe needles down to 25-gauge. The concentration of nucleated cells was adjusted to 0.5 to 1 X 101 cells.per ml by the addition of appropriate volumes of a culture medium (16) containing 5 ml of fetal-bovine serum, 2.5 ml of 7.5% NaHCO3, 1 ml of 200 mM iglutamine, 2 ml of penicillinstreptomycin (5000 units of each per ml), 86.7 ml of NCTC-109 medium (all of the preceding components were obtained from Microbiological ...