Embryonic Erythroid Cells Research Articles

The mouse beta h1 gene codes for the z chain of embryonic hemoglobin.

Beta h0 and beta h1 are two beta-like globin genes in the mouse beta-globin gene cluster whose functions have not previously been established. Transcripts of both beta h0 and beta h1 are found in yolk sac-derived erythroid cells from mouse embryos and in the murine erythroleukemic cell line GM979. S1 nuclease analysis shows that beta h1 is the more abundant of the two transcripts in both embryonic erythroid cells and the cell line GM979. Hybridization of a beta h1-specific probe to RNA from erythroid cells of 10-, 11-, 12-, 13-, and 14-day-old mouse embryos indicates that levels of beta h1 mRNA are high at 10 and 11 days and then decline during further fetal development. The in vitro translation product of hybrid-selected beta h1 mRNA was analyzed by acid/urea polyacrylamide gel electrophoresis. The beta h1 translation product has the electrophoretic mobility expected for the z chain. We conclude that beta h1 is a fully functional gene which codes for the embryonic z chain.

Analysis of rabbit β-like globin gene transcripts during development

We have analyzed the differential expression of a family of β-like globin genes during the development of rabbits, from four days post implantation to one week before birth. The family is composed of four genes, arranged 5′-β4-β3-Ψβ2-β1–3′ on the chromosome; Ψβ2 is an inactive pseudogene. Using the technique of hybrid-arrested translation in vitro, we have identified the embryo-specific globin polypeptides encoded by genes β3 and β4. The β3 and β4 globins are replaced by the adult β1 globin halfway through gestation; this corresponds temporally with the switch in site of erythropoiesis from the embryonic yolk sac to the fetal liver. The decline in production of β3 globin polypeptide precedes the decline in β4 globin. Transcripts from genes β1, β3 and β4 were analyzed at progressive stages of gestation by a blot-hybridization assay and by an S 1 nuclease protection assay. Mature messenger RNA and presumptive precursor RNAs from genes β3 and β4 are synthesized abundantly in embryonic erythroid cells but only at very low levels later in fetal development. Conversely, precursor and mature mRNA from gene β1 are found at very low levels in embryos but are abundant in fetal and adult erythroid cells. The co-ordinate appearance of precursor RNA, mRNA and polypeptide from all three active genes indicates that the primary developmental regulation of this gene family is exerted at the level of transcription. RNA species larger than the expected precursors were observed when the RNA was denatured with formaldehyde but not when methylmercury was the denaturant. These large RNAs are a formaldehyde-generated artifact, possibly a result of cross-linking globin transcripts to ribosomal RNA. We observe no extensive stable transcripts from the 5′ or 3′ flanking regions of these genes.

Translational control of ferritin synthesis by iron in embryonic reticulocytes of the bullfrog.

The regulation of ferritin synthesis by iron was examined in the reticulocytes of bullfrog tadpoles where the induction was 40- to 50-fold, increasing from 0.17 +/- 0.05% of total protein synthesis ([3H]leucine incorporation in cell suspension) to 7.4 +/- 1.6% following intraperitoneal injection of ferric ammonium citrate. No significant difference was observed between the levels of ferritin mRNA in control or iron-induced cells, determined by translation of isolated mRNA in a wheat germ system, demonstrating that ferritin induction by iron occurs by a post-transcriptional mechanism. Total protein synthesis in the wheat germ system was half-saturating at 10 micrograms of mRNA/ml whereas ferritin synthesis increased linearly up to 40 micrograms of mRNA/ml, demonstrating that the ferritin mRNA is translated with high efficiency relative to the total proteins synthesized. Studies with the cap analogue 7-methylguanosine-5'-monophosphate, suggest that cap binding is not directly involved in the high translational efficiency of the ferritin mRNA in the wheat germ system. The results indicate that iron-modulated changes in the availability of ferritin mRNA for translation, coupled with the high translational efficiency of the ferritin message, can account for the induction of ferritin synthesis by iron in embryonic erythroid cells.

Expression of Embryonic Haemoglobin in ts AEV-Transformed Embryonic Erythroid Cells During Temperature-Induced Differentiation

Cells prepared from 1-day-old chick blastoderms were infected with a temperature-sensitive mutant of avian erythroblastosis virus (tsAEV). Clonal strains of transformed erythroblasts were isolated from the infected blastoderm cells. By shift to the nonpermissive temperature, these cells could be induced to differentiate into erythrocyte-like cells which expressed embryonic haemoglobins. Embryonic haemoglobins could not be detected in tsAEV-transformed erythroblasts from adult bone marrow when induced to differentiate under the same conditions. In contrast to normal primitive erythrocytes, tsAEV-infected embryonic erythroblasts differentiated in vitro expressed also adult haemoglobin. These results suggest an influence of the haematopoietic environment on the switch from embryonic to adult erythrocytes.

Structural associations of synemin and vimentin filaments in avian erythrocytes revealed by immunoelectron microscopy

Intermediate filament structure and distribution were studied by antibody decoration and low-angle shadowing of sonicated chicken erythrocytes and embryonic erythroid cells. Intermediate filaments containing vimentin and synemin form a three-dimensional network in these cells, interlinking the nucleus and plasma membrane. This filament network is spatially segregated from the marginal band of microtubules, indicating that these two systems do not interact directly in the development or maintenance of cell shape. Incubation of sonicated cells with an antiserum specific for vimentin results in uniform decoration of the intermediate filaments; incubation with antisynemin results in decoration of periodically spaced foci. Measurement of the synemin periodicity under a specified set of sample preparation conditions gives average values of 180 nm for adult erythrocytes and 230 nm for 10 day old embryonic erythroid cells, suggesting some fundamental change in the structure of the filaments during erythropoiesis. Registration of these foci in laterally associated filaments, and decoration of bridges between slightly separated filaments, suggest that synemin mediates crosslinking of intermediate filaments through self-interaction.

Embryonic-fetal erythroid characteristics of a human leukemic cell line.

We have studied a number of cell surface, enzyme, and protein markers in the human leukemic K562 cell line. We have confirmed previous observations that these cells accumulate human embryonic hemoglobins after exposure to hemin. In addition, our results demonstrated that these cells possess in the "ininduced" state i surface antigen, lactate dehydrogenase isoenzymes characteristic of embryonic or fetal erythroid cells, fetal and embryonic globin chains, and globin mRNAs. The levels if i antigen, embryonic globin chains, and embryonic globin mRNA increased substantially after exposure of the cells to hemin in suspension culture. In contrast, K562 cells lacked several surface, enzymatic, and functional properties typical of granulocytes, lymphocytes, monocytes, or adult erythroblasts, including HLA surface antigens, surface immunoglobulins, sheep erythrocyte rosetting, phagocytosis, terminal deoxynucleotidyl transferase, carbonic anhydrase, ABO and Rh blood groups, and adult hemoglobins. The K562 cell line therefore exhibits phenotypic properties of embryonic erythroid progenitor cells and a quantitative increase in the expression of some of these properties can be achieved by exposure of the cells to hemin.

Haemoglobin-oxygen affinity in developing embryonic erythroid cells of the mouse

Haemoglobin-oxygen equilibrium curves have been measured in developing embryonic mouse erythroid cells. At 11.5 days gestation, shortly after blood islands from the yolk sac have formed but before the placenta is complete, erythrocytes have a high affinity for oxygen and a reverse Bohr effect below pH ∼7.0 (Figs. 1, 2, 3). By 13.5 days both the Bohr shift and the shape of the equilibrium curves are similar to those obtained from adult mice. From 13.5 days onwards, 2,3-diphosphoglycerate plays an important role in regulating oxygen affinity (Figs. 2, 4). It is suggested that the oxygen equilibrium properties of embryonic erythrocytes are adapted to service the developing embryo with oxygen under hypoxic and hypercapnic conditions in the intra-uterine environment up until the time when the embryonic circulation makes contact with the placenta.

Antigenic marker of human erythrokaryocytes similar to mouse erythroblast antigen

Identical antigenic determinants are discovered on the surface of human erythrokaryocytes with antibodies against specific antigen of murine erythroblasts (Ag-Ed), previously revealed in study of Rauscher leukemia, in the immunofluorescent and cytotoxic tests. The antigen is present on the membranes of the majority of human embryonic liver and adult bone marrow nuclear erythroid cells, but is not found in fetal thymocytes, newborn kidney cells, adult human hepatic cells and in peripheral blood erythrocytes. Ag-Eb appears to possess an inter-species determinant, shared by mammalian nuclear erythroid cells, and may be used as their specific marker.

Translation of endogenous message in embryonic chick erythroid cell polysomes in a cell-free protein-synthesizing system.

Polysomes from 5.5-day and 6.5-day embryonic chick erythroid cells contain messenger RNA (mRNA) which can be translated into products in a cell-free protein-synthesizing system. The products of the cell-free system coelectrophoresed with carrier globin chains from the cells from which the polysomal pellet was isolated. Wheat germ S30 fraction increases by 1.5--2.0 fold [3H] leucine incorporation into trichloroacetic acid-precipitable material directed by the endogenous mRNA on chick erythroid cell polysomes. The wheat germ probably provides a specific factor or factors absent in a shortage in the incubation medium.

Changes in the composition of plasma membrane proteins during differentiation of embryonic chick erythroid cell.

Erythroid cells which are homogeneous with regard to stage of maturation are naturally available from the circulation of chick embryos at various times of development. This provides a convenient system for examining the changes in plasma membrane protein composition during red cell maturation. Plasma membranes are isolated from chick embryonic erythroid cells at various stages of maturation. Extensive characterization of the isolated membranes show that they are pure and their proteins undegraded. Analyses by sodium dodecyl sulfate/polyacrylamide gel electrophoresis show that both qualitative and quantitative changes occur in membrane protein composition during the early stage of erythroid differentiation. Specific proteins of red cell membrane such as "spectrin" and band three proteins are present in low levels in early erythroblasts but increase in their relative amounts with maturation. A steady-state membrane protein composition seems to be established by the late polychromatophilic erythroblast stage.

Kinetics of development of embryonic erythroid cells.

ABSTRACTEmbryonic erythropoiesis is an intrinsically non‐steady‐state process. A method of non‐steady‐state analysis is employed to approximately determine the kinetics of maturation of embryonic erythroid cells during the hepatic phase of erythropoiesis in the mouse.It appears from this analysis that embryonic erythroid cells have significantly shorter maturation times than their adult counterparts. In the embryo, there is insufficient time for more than three divisions between the proerythroblast and the orthochromatic erythroblast.

Stimulation of haem synthesis by erythropoietin in mouse yolk-sac-stage embryonic cells

ABSTRACT Cultures of disaggregated cells from mouse embryos at the stage of yolk-sac erythropoiesis have been used to test sensitivity of primary erythroid cells to erythropoietin, the hormone which controls adult red cell production. Synthesis of haem was stimulated by 89% in cells of 8-day embryos, 23 % in cells of 9-day embryos and by 19% in peripheral nucleated blood cells of 12-day embryos. Differentiation of primary embryonic erythroid cells may therefore be controlled by erythropoietin in situ. The haem precursor δ-aminolaevulinic acid (ALA) did not stimulate haem synthesis under similar conditions.