Nucleotide polymerases in the developing avian erythrocyte

Avian erythroid cells were separated into five developmental stages by sedimentation on discontinuous isotonic albumin gradients. Solubilized enzyme activities from whole cells were partially purified and characterized by ion exchange and ion filtration chromatography and velocity sedimenttation analysis. Three nucleotide polymerase types were investigated: (a) DNA-dependent RNA polymerases; (b) RNA-dependent terminal ribonucleotidyltransferases, and (c) DNA-dependent DNA polymerases. The two characteristic forms of eucaryotic DNA-dependent RNA polymerases, polymerase I (nucleolar) and polymerase II (nucleoplasmic), were identified. Polymerase III was only marginally detectable even in the earliest developmental populations. At least two species of RNA-dependent terminal ribosyltransferases were present. One apparently was the poly(A) polymerase observed in other systems. The other terminal transferase was present in two chromatographic forms, required an RNA primer, and used UTP and/or CTP as particularly efficient substrates. Three DNA polymerase activities were resolved, two of which were characteristic of the alpha and beta DNA polymerases described in other eucaryotic systems. The third polymerase was not the gamma polymerase but a separate entity. Poly(dC)-dependent RNA polymerase activity, associated with the alpha polymerase, was relatively enriched in the third DNA polymerase species. The activity levels of the nucleotide polymerases were monitored as a function of red cell maturation. Characteristic declining patterns of activity were obtained for each enzyme which correlate well with the synthetic rates of their in vivo products where these are known. These results correlate well with the synthetic rates of their in vivo products where these are known. These results are consistent with the postulate that the general transcriptive and replicative control processes operating during development may involve changes in the level of the requisite polymerases.

Alterations in the numerical density of perichromatin granules in different tissues during ageing and cell differentiation

Perichromatin granules (PG) were counted on electron micrographs of different tissues taken from young and old female Wistar rats as well as in the basal and spinous layers of adult human epidermis. A significant age-dependent decrease was observed in the following cell types: large brain cortical cells, cerebellar granular cells, hepatocytes, parotid gland cells. No significant decrease was found in the heart muscle nuclei and in the erythroblasts of identical maturation level. The number of PG decreased during the erythroblast maturation almost to zero, and increased in the cells of spinous layer of human epidermis as compared to the basal cells. There is a very wide variation in the number of PG per nucleus between the different tissues. The correlation between the transcriptional activity, the protein synthesis, ageing and cell differentiation is discussed.

Erythroid precursor fusion induced by Sendai virus

The ultrastructural events of the interaction of Sendai virus (SV) with fetal mouse erythroid precursors, and SV-induced fusion of erythroid precursors at different maturation stages are described. SV was shown to affect the erythroid nuclei causing interruption of the nuclear membrane, enlargement of the nucleolus and nuclear fusion. SV induced fusion also between dividing and non-dividing cells.

Comparative ultrastructure of late rabbit-embryo erythroid cells in liver and peripheral blood

A morphological study of hemoglobin biosynthesis activity in rabbit-embryo liver and peripheral blood was comparatively developed. Orthochromatic erythroblasts and reticulocytes of the same maturing degree were analysed through thin sections, as to their organellar constitution and behaviour regarding iron incorporation. It was found that peripheral blood erythroid cells contain mainly hemosomes, organelles taken as sites of final hemoglobin molecule biosynthesis. The ratio between the mean number of hemosomes in blood erythroid cell sections and that in liver erythroid cell sections reaches a little more than 6:1. Inversely, late liver erythroid cells are predominantly constituted by mitochondria that directly or indirectly participate in hemosome formation. The ratio between the mean number of mitochondria in blood erythroid cell sections and that in liver erythroid cell sections reaches 1:11. Besides this, the iron incorporation activity is higher in peripheral blood erythroid cells than in liver erythroblasts and reticulocytes. It is apparent that erythroid cells in the liver accumulate heme, given the ratio of the means of iron incorporation activity per cell to hemosome per cell (3.67), while blood erythroid cells, with a 1.08 ratio, synthesize heme, which is immediately afterwards integrated into the globin chains. The sudden increase in the formation of hemosomes when liver orthochromatic erythroblasts and reticulocytes enter the peripheral blood, reflecting an enhancement of hemoglobin synthesis, agrees with biochemical findings of other authors.

Comparative electron-microscopic study of the erythrocytic line in refractory anemia (preleukemia) and myelomonocytic leukemia

The bone marrow erythrocytic precursors of 12 patients with refractory anemia (preleukemia) or myelomonocytic leukemia were studied by transmission electron microscopy. The results were tabulated in a semiquantitative manner and a comparison was established between the two main diagnostic groups. The following results are reported. 1. Similar nuclear and cytoplasmic abnormalities of the normoblasts were observed in preleukemia and leukemia. 2. A nuclear lesion consisting of nuclear clefts and blebs was demonstrated in at least some of the normoblasts in all of the patients. Although not specific, this finding appears to be a new contribution in the field of preleukemia and myelomonocytic leukemia. 3. Iron overload, including the presence of pathologic sideroblasts, is common to both preleukemia and leukemia.

Congenital hypoplastic anaemia with unusual dyserythropoietic features. A case report

A case of severe congenital anaemia (Hb levels 3--4 g/dl) is presented. The patient, a 21-year-old female, requires, since the age of two, periodical blood transfusions, but is nevertheless able to lead a normal life as a housewife. Although the case has to be considered as a form of congenital hypoplastic disorder of the erythroid tissue, some of the clinical and haematological features are compatible with a congenital dyserythropoietic state. On the basis of clinical findings it is suggested that it may represent a previously undescribed form of anaemia which shares the features of both hypoplastic and dysplastic congenital affections of erythropoiesis.

Electron microscope and high resolution autoradiographic studies of megaloblastic erythropoiesis

Bone marrow fragments from 10 patients with a megaloblastic anaemia due to vitamin B12 or folate deficiency were studied by electron microscopy and electron microscope autoradiography. A proportion of the erythroblasts showed ultrastructural abnormalities. Some of the cells containing autophagic vacuoles, large siderosomes, iron-laden mitochondria, irregularly shaped nuclei, membrane-bound nuclear clefts, or incomplete nuclear membranes were found to be capable of DNA, RNA and protein synthesis. Other cells showed advanced degenerative changes such as the distension of the perinuclear space, the clumping of cytoplasmic organelles near the nucleus and a reduction in the electron density and ribosome content of the cytoplasm. Most of these grossly abnormal cells suffered from either a marked depression or an arrest in protein and RNA synthesis, and were presumably destined for phagocytosis by reticulum cells.

[Congenital dyserythropoietic anemia type II. Another case report]

Hematologic evaluation of a 29-year old man with jaundice since childhood demonstrated the characteristic findings of congenital dyserythropoietic anemia (CDA) type II. This type is characterized by ineffective erythropoiesis, multinuclearity of erythroblasts, electron-microscopic abnormalities of the red cell membrane, and abnormal serological reactions. Because of severe anemia repeated transfusions were necessary. After splenectomy thrombosis of the portal vein occurred. The patient died from hemorrhage due to ruptured esophageal varices.

The morphology of dyserythropoiesis in a patient with acute erythroleukaemia associated with multiple myeloma

A patient with multiple myeloma in whom acute erythroleukaemia developed 5 years following treatment with irradiation and melphalan is reported. Immunoglobulin synthesis and immunofluorescence investigations provided evidence that the blast cells in the peripheral blood did not belong to the plasma cell series; ultrastructure examination demonstrated their myeloid origin. Chromosomally abnormal cells were observed in both the bone marrow and peripheral blood. Light-and electron microscopy of erythropoiesis in this case showed distinct features of dyserythropoiesis, similar to those described in other entities. The erythroid cell abnormalities are discussed in the light of their being either indications of malignancy or of a reactive process.

Experimental induction of erythroblastemia using intravenous carbonyl iron particles

An experimental model is presented whereby erythroblastemia, the appearance of nucleated red cells in circulation, was induced reproducibly in rabbits by intravenous injection of 0.5 to 1 g/kg carbonyl iron particles (CIP). The phenomenon reached a peak in 24 to 48 hours and disappeared after a week. Erythroblastemia was associated with evidence for disseminated intravenous coagulation; both could be aborted by administration of heparin. Repeated injection of CIP was always followed by recurrence of erythroblastemia. For a period as long as 7 months, the animals tolerated repeated injections without evidence of lasting sequelae. Electron microscopic studies of marrow tissue indicated alterations in the red cell nuclei but no alterations in the endothelium of marrow sinuses into which the red cells migrate to reach the circulation. This model provides a means to study the mechanisms involved in nuclear elimination by mammalian red cells.

Xenogenization of rat erythroid cells by lymphatic leukemia virus: its role in induction of autoimmune hemolytic anemia

Newborn rats given injections of low doses of Friend lymphatic leukemia virus subsequently developed hemolytic anemia characterized by production of antierythrocyte autoantibody. Electron microscopy showed C-type virus particles budding from the cell membrane not only of lymphoid cells but also of erythrocyte percursor cells in bone marrow and spleen, suggesting that the erythroid cells were infected by the virus. In addition, erythrocyte precursor cells expressed virus-induced cell surface antigens detected by cytotoxicity tests. Normal syngeneic rats preimmunized with a Friend lymphatic leukemia virusinduced tumor and subsequently inoculated with bone marrow, spleen cells, or reticulocyte-rich fraction derived from other rats injected with high doses of the virus at birth produced cytotoxic antibody to the virus-induced tumor and antierythrocyte autoantibody. In contrast, rats subsequently inoculated with virus-infected thymus or lymph node cells produced cytotoxic antibody but not antierythrocyte autoantibody. These results indicate that "xenogenization," previously shown for tumor cells and normal lymphoid cells, is also observed for rat erythroid cells and, further, that xenogenization of erythroid cells by Friend lymphatic leukemia virus is one of the most important factors in induction of autoimmune hemolytic anemia.

Intercellular contacts between erythroid precursors in the bone marrow in dyserythropoiesis

The ultrastructure of the cellular interfaces between erythroid precursors has been studied in both congenital and acquired dyserythropoiesis. The types of cell-to-cell contacts found included highly convoluated interdigitating septate-like junctions as well as apparent confluence of the cellular membranes of adjacent erythroid cells. Such findings are not characteristic of the intercellular relationships found in the normal erythroblastic islands. The erythroid plasma membrane modifications are possibly related to the changes in the plasma membranes of erythroid cells known to occur in dyserythropoiesis and their presence may well contribute to the ineffective erythropoiesis with intramedullary cell destruction which characterizes many dyserythropoietic states.

[Congenital type II dyserythropoiesis]

The authors report a case of congenital dyserythropoieses, type II, the diagnosis of which was made in a young 15 year old girl with anemia, sub-clinical jaundice and splenomegaly. The following three criteria were found: erythroblastic hyperplasia with a high percentage of binuclear cells, a double peripheral red cell membrane under the electron microscope and a positive Ham-Dacle test. An isotopic study showed a double process or erythropoiesis which was inefficacious and peripheral hemolysis. In connection with this case, the authors then recall the main characteristics of the three types of congenital dyserythropoiesis. The origin and consequences of the peripheral membrane excess of the erythroblasts characteristic of type II are then discussed.

Changes in number, mobility, and topographical distribution of lectin receptors during maturation of chick erythroid cells

Plant lectins have been used to probe changes in cell surface characteristics that accompny differentiation in a complete series of chick erythroid cells. Dramatic differences in lectin receptor mobility were observed between the most immature cells of the series, the proerythroblasts, and cells at the next stage of maturation, the erythroblasts. Both concanavalin A and Ricinus communis agglutinin form caps on proerythroblasts, whereas they develop a patchy distribution on erythroblasts. Erythroid cells at later developmental stages show a homogeneous distribution of surface-bound R. communis agglutinin. Concanavalin A also shows a uniform distribution on the cell periphery, but appears to be concentrated in a ring above the perinuclear region of the cell. In addition to changes in mobility of lectin receptors, a large reduction (50-70%) in the number of lectin receptors per cell accompanies maturation of proerythroblasts to erythroblasts. Pretreatment of the cells with neuraminidase results in enhanced binding of R. communis agglutinin to proerythroblasts. The number of additional R. communis agglutinin receptors exposed by enzyme treatment remains relatively constant during subsequent cell maturation.

Multiple vacuoles formation in erythroblasts in an erythroleukaemic patient

Peculiar erythroblasts with multiple vacuoles were observed in the bone marrow of an erythroleukaemic patient. Some erythroblasts contained more than 80 vacuoles on a thin section. The contents of vacuoles were amorphous with low electron density. No transitional form from mitochondria or other organelles was observed. Since these vacuolated erythroblasts were clearly distinguishable from megaloblastoid erythraemia cells, multiple vacuoles formation is presumably attributable to the disturbance of microconnection net work in the normal red cell series.

[Heterogeneity of the cellular distribution of erythrocytic A antigens. Ultramicroscopic study]

A and A1 antigens have been detected on cells of the human erythrocyte series by immunoelectron microscopy. These antigens have been revealed by an indirect method involving various anti-A and anti-A1 antibodies (allo, auto, hetero-antibodies) and peroxidase-conjugated anti-immunoglobulin antibodies. Immunologic labelling has been carried out with erythrocyte or bone marrow cell suspensions which were fixed prior to incubation with reagents. Cells from various A phenotypes were examined. A and A1 antigens were visualized on maturing normoblasts, at every developmental stage. In addition cell to cell variations of the surface labelling of erythrocytes was found in normal phenotypes, suggesting the existence of several populations of cells according to antigenic load.

Congenital dyserythropoietic anemia type II. Radioautographic, ultrastructural and cytogenetical study in two familial cases

The case of two sisters is reported in whom morphological (multinucleated erythroblasts in the bone marrow) and serological (positive Ham test, negative sucrose and water-sugar tests) characteristics of a congenital dyserythropoietic anemia type II were found. Radioautographic, cytogenetic and electron microscope studies confirmed the presence of an inefficient erythropoiesis and of a membrane defect, common in this disease. The finding of a nil LAP score has never been reported so far.

Cellular composition of erythropoietic cell populations and aggregate cell cultures derived from early chick blastodiscs

Light and electron microscopy of suspensions of cells prepared by dispersing chick blastodiscs at primitive-streak and head-fold stages showed the presence of numerous yolk granules, yolk-rich endodermal cells and occasional presumed ecto- and mesodermal cells. Several cell fractions prepared from this suspension by sedimentation through discontinuous Ficoll gradients were of similar composition. No enrichment of any particular cell type which might account for either differential sedimentation or erythropoietic potential of the fractions could be recognized. Two fractions, EP 1, and EP 2, were cultured as cell aggregates on vitelline membranes. EP 1 produced highly organized blood islands containing developing erythrocyte cells, organized endothelium, fibroblasts, thrombocytes and occasional granulocytes. Blood islands derived from EP 2, on the other hand, contained essentially only aggregates of erythroblasts embedded in endoderm. It is tentatively suggested that EP1 contains young multipotential hematopoietic precursors while EP 2 has only older blood-cell precursors committed to erythrocyte development. No cellular basis for the resolution of EP 1 into two complementary subfractions could be recognized.

The erythroid cells of anaemic Xenopus laevis. I. Studies on cellular morphology and protein and nucleic acid synthesis during differentiation

Phenylhydrazine has been used to induce anaemia in Xenopus laevis. The dosage used causes the complete destruction of all mature erythrocytes within twelve days. The anaemia results in the initiation of a wave of erythropoiesis and large numbers of immature erythroid cells are released into the circulation. The morphological and biosynthetic changes which these cells undergo as they differentiate in circulation are described. The origin of the circulating erythroid cells is also discussed.