The effect of various stage maturity of erythrocytes upon proliferatio rate of erythroid cells in "crown" of erythroblastic islands

Joint cultivation of small amounts of young and mature erythrocytes with bone marrow erythroblastic islands during 24 hours in liquid culture system results in erythropoiesis stimulation due to increase of number of cells in the state of mitosis in island's "crown". Prolonged joint cultivation and/or joint cultivation with plenty of premature and mature erythrocytes leads to inhibition of the erythropoiesis in the state of mitosis in the island's "crown". The maximum of the inhibitory effect was shown by erythrocytes from polycythemia rats.     

Dynamic changes of erythropoietin and tumor necrosis factor-alpha levels in peripheral blood and their correlation with erythropoiesis changes in posttransfusion polycythemia in animals

Posttransfusion polyglobulia reveals elevated level of the tumor necrosis factor-alpha in peripheral blood, suppresses erythropoiesis in bone marrow erythroblastic islands by diminishing the newly forming erythroblastic islands, and suppresses erythropoietin production in rats.     

Erythropoietin and phagocyte activity of central macrophage of the erythroblastic island in rats

Administration of erythropoietin enhanced the intensity of the phagocytosis in the erythroblastic island. The effect was more evident in case of normal erythropoiesis. The phagocyte activation of the central macrophage erythroblastic island was shown to depend on the condition of erythropoiesis in the erythroblastic island crown.     

Activity of nucleolar organizers in central macrophage culture of bone marrow erythroblastic islands

The erythroblastic islands of the bone marrow are morphofunctional units of erythropoiesis. In this work the functional state of erythroblastic islands' cells of the bone marrow, for the first time, was defined by the estimation of the activity of the nucleolar organizers of central macrophages in the erythroblastic islands, cultivated during 24 and 48 hours with the presence of various doses of erythropoietin. The findings indicated that the increase in doses of erythropoietin was accompanied by the corresponding increase of the activity of nucleolar organizers in central macrophages of erythroblastic islands. The nucleolar organizers of central macrophages in cultures of erythroblastic islands responded to very small doses of erythropoietin by their activation.     

Klf1 affects DNase II-alpha expression in the central macrophage of a fetal liver erythroblastic island: a non-cell-autonomous role in definitive erythropoiesis

A key regulatory gene in definitive erythropoiesis is the erythroid Kruppel-like factor (Eklf or Klf1). Klf1 knockout (KO) mice die in utero due to severe anemia, while residual circulating red blood cells retain their nuclei. Dnase2a is another critical gene in definitive erythropoiesis. Dnase2a KO mice are also affected by severe anemia and die in utero. DNase II-alpha is expressed in the central macrophage of erythroblastic islands (CMEIs) of murine fetal liver. Its main role is to digest the DNA of the extruded nuclei of red blood cells during maturation. Circulating erythrocytes retain their nuclei in Dnase2a KO mice. Here, we show that Klf1 is expressed in CMEIs and that it binds and activates the promoter of Dnase2a. We further show that Dnase2a is severely downregulated in the Klf1 KO fetal liver. We propose that this downregulation of Dnase2a in the CMEI contributes to the Klf1 KO phenotype by a non-cell-autonomous mechanism.     

Absence of erythroblast macrophage protein (Emp) leads to failure of erythroblast nuclear extrusion

In mammals, the functional unit for definitive erythropoiesis is the erythroblastic island, a multicellular structure composed of a central macrophage surrounded by developing erythroblasts. Erythroblast-macrophage interactions play a central role in the terminal maturation of erythroblasts, including enucleation. One possible mediator of this cell-cell interaction is the protein Emp (erythroblast macrophage protein). We used targeted gene inactivation to define the function of Emp during hematopoiesis. Emp null embryos die perinatally and show profound alterations in the hematopoietic system. A dramatic increase in the number of nucleated, immature erythrocytes is seen in the peripheral blood of Emp null fetuses. In the fetal liver virtually no erythroblastic islands are observed, and the number of F4/80-positive macrophages is substantially reduced. Those present lack cytoplasmic projections and are unable to interact with erythroblasts. Interestingly, wild type macrophages can bind Emp-deficient erythroblasts, but these erythroblasts do not extrude their nuclei, suggesting that Emp impacts enucleation in a cell autonomous fashion. Previous studies have implicated the actin cytoskeleton and its reorganization in both erythroblast enucleation as well as in macrophage development. We demonstrate that Emp associates with F-actin and that this interaction is important in the normal distribution of F-actin in both erythroblasts and macrophages. Thus, Emp appears to be required for erythroblast enucleation and in the development of the mature macrophages. The availability of an Emp null model provides a unique experimental system to study the enucleation process and to evaluate the function of macrophages in definitive erythropoiesis.     

Effect of acute congestive splenomegaly on erythropoiesis in rats

Spleen veins ligature (SVL) led to acute congestive splenomegaly in rats with subsequent normochromic anaemia disappearing on the 21st day after the SVL. An appreciable depression of the bone marrow erythropoiesis, particularly of the so called "proliferating erythroblastic islets" number, was evident on the 7th and 14th days of post-SVL period. The post-SVL anaemia was also associated with occurrence of the "islets" missing central macrophages and eosinophil-enriched "islets" in bone marrow.     

the effect of colonystimulating macrophage factor on activity of the nuclear organisers in central macrophages of the cultures of the bone marrow erythroblastic islands

Erythroblastic islands of the bone marrow are morpho-functional units of erythropoiesis. The functional state of erythroblastic islands' cells of the bone marrow was for the first time defined by estimation of activity of the nuclear organisers of the central macrophages in the erythroblastic islands cultivated for 24 hrs in presence of various doses of the colony-stimulating macrophage factor. The findings indicate that increased doses of the colonystimulating macrophage factor was accompanied by a respective enhancement of the activity of nucleolar organisers in central macrophages of erythroblastic islands.     

Hybrid Model of Erythropoiesis

A hybrid model of cell dynamics is presented. It is illustrated by model examples and applied to study erythropoiesis (red blood cell production). In this approach, cells are considered as discrete objects while intra-cellular proteins and extra-cellular biochemical substances are described with continuous models. Spatial organization of erythropoiesis occurring in specific structures of the bone marrow, called erythroblastic island, is investigated.     

Sites of aluminum accumulation in bone marrow: study using electron microscopy, ionic microscopy and X-ray microanalysis

Two methods of analytical microscopy have been used to study the distribution of aluminum in bone marrow of rats intoxicated by aluminum gluconate. Images of the distribution of aluminum in a field of 250 microns in diameter were obtained by analytical ion microscopy. They show that this element was concentrated in spots, associated with iron or alone, in the cytoplasm of some cells. Electron Probe Microanalysis (EPMA) has shown that aluminum concentration occurred in cells of the reticulo-endothelial system, principally in the reticular cells of erythroblastic islets. In cells of the reticuloendothelial system, aluminum was observed in intracytoplasmic organelles having ultrastructural characteristics of lysosomes or phagolysosomes. In these organelles, aluminum is always associated with phosphorus and sometimes with iron. No cytoplasmic or nuclear aluminum accumulation was detected in any other variety of bone marrow cells. The consequences of the selective accumulation of aluminum in the cytoplasm of reticular cells of erythroblastic islets for the maturation of erythrocytes are discussed.     

THe dynamics of erythropoiesis inhibition in posttransfusion polycythaemia in the rat

The dynamics of erythropoiesis inhibition as the consequence of polycythaemia induced in rats by four to six transfusions of homologous erythrocytes was studied in detail. It was found, that, in rats with polycythaemia elicited by two transfusions of erythrocytes, erythropoiesis inhibition occurs 67h after the first transfusion and it is most pronounced in the period between 115-187 h. The hemopoietic system is not completely free from the inhibitory influence of polycythaemia up to 283 h after the first transfusion. Maintenance of a state of polycythaemia for 17 days by repeated transfusions strongly and durably inhibits the haemopoietic system. The red blood cell system remained for this whole period under the inhibitory effect.     

Ultrastructural Aspects of Erythropoietic Differentiation in Long-term Bone Marrow Culture

Long-term liquid cultures of mouse bone marrow produce stem cells (CFU-S) and differentiated granulocytes for many months. Addition of AMS (anaemic mouse serum) to the cultures almost entirely eliminates the granulopoietic activity and stimulates erythropoiesis, with full erythroid maturation and the production of adult haemoglobin. Ultrastructural analsysis of in situ fixed material reveals the cell shape and surface morphology of the erythroid maturation series, and the generation of erythroblastic islands in vitro. Each erythroblastic island consists of one or more synchronously maturing cohorts of erythroid cells undergoing four or five divisions between proerythroblast and normoblast. Each island is centered on a macrophage, which interacts with the developing erythroid population in several ways. Expelled nuclei are phagocytosed by the macrophage, which also has large areas of closely apposed membrane with the erythroid cells, gap junctions, and possible reciprocal vesicular activity. Changes in the adherent layer (stromal cells) also occur with the transition from granulopoiesis to erythropoiesis. There is a reduction in the endothelial cell cover, and mobilisation of lipid from the granulopoietic associated apidocytes.     

Erythropoietic function of the kidneys under conditions of abnormally high oxygen pressure]

Three to five hours after 5-hour exposure of rabbits to high oxygen pressure (2 ata) the erythropoietin proved to disappear from both the arterial and the venous blood plasma of the kidneys. At the same time the blood plasma from the renal vein began to suppress the mitotic activity of erythroblastic cells in the bone marrow culture. These data testify to the fact that under hyperbaric hyperoxia the kidneys secreted the inhibitor of erythropoiesis. No erythropoiesis inhibitor was revealed 24 hours after the hyperoxia.     

Kupffer cells support extramedullary erythropoiesis induced by nitrogen-containing bisphosphonate in splenectomized mice

Our previous study indicated that injecting nitrogen-containing bisphosphonate (NBP) induced the site of erythropoiesis to shift from the bone marrow (BM) to the spleen. This was due to the depletion of BM-resident macrophages, which support erythropoiesis. In this study, we examined NBP treatment-induced extramedullary hematopoiesis in splenectomized mice, focusing on hepatic hematopoiesis. NBP-treated mice did not display anemia or significant change in erythropoietin production, while megakaryopoiesis and erythropoiesis were constantly observed in the liver. Erythroblastic islands were detected in the sinusoidal lumen. Kupffer cells expressed VCAM-1 following NBP treatment, which is an important factor for erythroblast differentiation. Cl₂MBP-liposome treatment depleted the erythroblastic islands, and decreased the number of hematopoietic cells in the liver, as determined by colony forming assays. Together, these results indicate that Kupffer cells support erythropoiesis, acting as stromal cells in the liver, and that they might act as a niche for hematopoietic precursor cells in an emergency.     

Classification of erythroblastic islets of the bone marrow and the study of their cellular composition

Cell composition of erythroblastic islands (EI), normal and at the phase of stimulation and inhibition of erythropoiesis at modelling of heat adaptation has been studied on hemopoietic tissue of 108 rats. In the hemopoietic tissue, together with EI of the 1st, 2nd and 3d classes of maturity, that have in their composition correspondingly up to 8, from 9 up to 16 and above 16 nuclei-containing erythroid cells, there are involutive and reconstructing EI. The involutive EI are presented as nuclei-containing erythroid cells, that are not able to divide and are at late stages of differentiation: polychromatophilic and oxyphilic normoblasts, as well as reticulocytes. The reconstructing EI have in their composition both erythroid cells, that are not able to divide, and erythroid cells (pro-, erythroblasts and basophilic normoblasts), that are at early stages of differentiation. Application of the EI classification suggested, takes into account the rate, with which the erythroid cell-predecessors are drawn into erythropoiesis and intensity of erythroid differentiation. Therefore, it is possible to obtain earlier and more exact data on the state of hemopoiesis in comparison with traditional hematological methods.     

Occurrence of microtubules during erythropoiesis in Llama, Lama glama

Studies on the ellipsoid erythroblasts of Llama, L a m gluma, L. during erythropoiesis showed the appearance of the marginal band composed of approximately 29 microtubules. As the maturation of erythrocytes goes on, the number of marginal band microtubules diminishes. No microtubules were found in mature erythrocytes of Llama.     

The switch from larval to adult globin gene expression in Xenopus laevis is mediated by erythroid cells from distinct compartments

The transition of hemoglobins during metamorphosis of Xenopus laevis involves replacement of the larval erythrocytes by adult ones, suggesting that the developmental control of this event depends upon the growth characteristics of the precursor cells. To identify the erythroid precursor cells and to investigate their developmental fate, we analyzed the distribution of stage-specific globin mRNAs by northern blotting in dorsal and ventral fragments of stage 32 embryos after in vitro culture as well as presumptive erythropoietic tissues of tadpoles during metamorphosis. The histological analysis shows that erythrocytes differentiate only in ventral fragments, suggesting that the ventral blood islands and most likely also the dorsolateral mesoderm are the primary sites of erythropoiesis. We also demonstrate that the first generations of erythrocytes, already express the predominating larval-specific alpha-globin mRNAs. The globin mRNA patterns obtained from presumptive erythropoietic tissues suggest an important role of circulating precursor cells in larval erythropoiesis, whereas the liver appears to be the main site of formation and maturation of the adult erythrocytes. Tentatively we propose that anuran erythropoiesis is dependent upon a self-perpetuating stem-cell line and that the larval and the adult erythrocytes are derived from successive generations of erythroid precursors, whose commitment may be imposed by the erythropoietic sites.     

The content of ribonucleoproteids in the bone marrow erythroblastic islands in various functional states of erythropoiesis

Erythroblastic islands of the bone marrow are morpho-fuctional units of erythropoiesis. The functional state of the erythroblastic islands' erythrokariocytes and central macrophages of the bone marrow was first studied by estimation of the content of ribonucleoproteids in its cells (Brashe reaction). Acute blood loss and posttransfusion polycytemia lead to enhancement of the content of ribonucleoproteids in erythrokariocytes and central macrophages of the bone marrow of the rates.