Onset Of Hemoglobin Synthesis Research Articles

Regulation of β-adrenergic responses during in vitro differentiation of mouse erythroleukemia cells

Dimethyl sulfoxide (DMSO)-induced erythroid differentiation of Friend mouse erythroleukemia (MEL) cells is associated with a marked transient modulation of catecholamine sensitivity. Within 24 h after induction and well before the onset of hemoglobin synthesis, we observed a 3-fold increase in β-receptor density and a more than 10-fold increase in receptor-coupled cAMP formation. During the following 4 days, in parallel with the development of normoblast-like cells, receptor numbers returned to preinduction levels while catecholamine-dependent cAMP formation remained significantly elevated. Simultaneously, the apparent potency of the β-adrenoceptor agonist isoprenaline increased 10-fold. Improved receptor—cyclase coupling is probably due to a major shift in the expression of G i and G s regulatory proteins. Bacterial toxin-mediated ADP-ribosylation of membrane proteins suggests that the dominating species in native cells is G i (G sα:G iα = 1:7). By contrast, G s predominates in differentiated cells (G sα:G iα = 1.8:1). Receptor-independent forskolin-stimulated cAMP formation showed a pronounced, albeit transient, decrease during differentiation. We suggest that these changes in cellular cAMP responses may be important for transient positive or negative cooperative interactions between hormones and growth factors in the course of erythroid cell development.

Immunofluorescence examination of beta tubulin expression and marginal band formation in developing chicken erythroblasts.

Chicken erythrocyte beta tubulin, a tubulin variant with unique biochemical and assembly properties, is found to be specifically contained in two chicken blood cell types--erythrocytes and thrombocytes. The beta tubulin variant is absent or present in low amounts in a variety of white blood cell types and other body tissues, as determined by immunofluorescence microscopy and a semi-quantitative immunoblotting procedure. During differentiation in the marrow the beta tubulin variant appears suddenly in mid-stage erythroblasts at the onset of hemoglobin synthesis, and forming marginal bands are seen in all subsequent polychromatophilic erythroblast stages. The developmental sequence of events in marginal band formation entails microtubule nucleation at the centrosome, followed by microtubule elongation, consolidation of loose parallel microtubules into a compact bundle, and microtubule association with the cell membrane.

Expression of Blood Group A Antigens in Human Bone Marrow Cells

We have studied the appearence of blood group A-activity during hematopoiesis in human bone marrow cells by the use of the blood group A-specific lectin from Vicia cracca. Cells that bound the lectin were identified using antiserum against the lectin followed by rosetting with protein A-containing Staphylococcus aureus cells. Only cells of the erythroid lineage from blood group A individuals formed staphylococcal rosettes. A-activity occurred in basophilic normoblasts and later stages of erythropoiesis, whereas pronormoblasts were negative. The appearance of blood group A-activity coincided roughly with the onset of hemoglobin synthesis and slightly later than the expression of the major sialoglycoprotein of erythrocytes, glycophorin A. Glycophorin A did not, however, contain blood group A-activity when analyzed by immunoprecipitation and gel electrophoresis.

Expression of blood group A antigens in human bone marrow cells

We have studied the appearance of blood group A-activity during hematopoiesis in human bone marrow cells by the use of the blood group A-specific lectin from Vicia cracca. Cells that bound the lectin were identified using antiserum against the lectin followed by rosetting with protein A-containing Staphylococcus aureus cells. Only cells of the erythroid lineage from blood group A individuals formed staphylococcal rosettes. A-activity occurred in basophilic normoblasts and later stages of erythropoiesis, whereas pronormoblasts were negative. The appearance of blood group A-activity coincided roughly with the onset of hemoglobin synthesis and slightly later than the expression of the major sialoglycoprotein of erythrocytes, glycophorin A. Glycophorin A did not, however, contain blood group A-activity when analyzed by immunoprecipitation and gel electrophoresis.

The tRNA content of non-hemoglobinized red cell precursors: Evidence that tRNA content is controlled by tRNA utilization

The content of tRNA's accepting several amino acids was determined for the non-hemoglobinized early precursors of rabbit red cells and was compared with the tRNA content of rabbit reticulocytes and liver. The specialization of the tRNA content for hemoglobin synthesis seen in reticulocytes was not seen in the earlier precursors, suggesting that tRNA specialization does not occur before the onset of hemoglobin synthesis. The results favor hypotheses that the tRNA content develops in response to tRNA utilization in translation.