Haemopoiesis in the human yolk sac

Haemopoiesis in human yolk sacs was examined using tissues obtained from a total of 27 cases in various stages of development from the fourth to eleventh week of pregnancy. In the early stages of development, the yolk sac was observed to be connected to the midgut by the vitelline duct, which became slender with later growth of the embryo. In the early stages of pregnancy, endodermal tissues were found to be a predominant component, whereas in the later stages, the mesenchymal tissues increased. The most immature blood cells and their mitotic figures were observed in the endodermal tissue. Haemopoiesis was found in endodermal tissue before mesenchymal tissue had developed. Electron microscopy revealed that maturation of the blood cells proceeded as the cells were formed in mesenchymal tissue and in blood vessels.

Preleukemia in Fanconi's anemia: hematopoietic cell multinuclearity, membrane duplication, and dysgranulogenesis

A 25-year-old male had Fanconi's anemia characterized by small stature, the onset of pancytopenia in the first decade of life, a high spontaneous breakage rate of the chromosomes, and the development of acute myeloblastic leukemia. In the preleukemic phase, marrow erythroblasts were multinucleated, and had duplicated nuclear and cytoplasmic membranes with frequent nuclear pockets and cytoplasmic vacuoles, respectively. All neutrophilic and eosinophilic granulocytes had severe quantitative and qualitative defects of granulogenesis; autophagy and nuclear pockets were also observed in the majority of granulocytic cells. Platelets had decreased granulation and extremely dilated canaliculi. Decreased titration scores with anti-I and anti-i were observed with the patient's erythrocytes and those of his clinically normal mother. The unusual morphologic and serologic findings in this patient appear to have resulted from a membrane abnormality affecting the cells of several hematopoietic lines and their organelles.

Ultrastructure of bone marrow in patients with visceral leishmaniasis

Ultrastructural studies were performed on bone marrow aspirates from three patients with visceral leishmaniasis. The patients were moderately anaemic but showed a suboptimal increase in the absolute reticulocyte count. Serum and red cell folate concentrations and serum vitamin B12 concentrations were normal in all three cases, and serum ferritin concentrations were normal or increased. The bone marrows were hypercellular and showed erythroid hyperplasia; a high proportion of the erythroblasts showed dyserythropoietic changes. Amastigote forms of Leishmania donovani were found within bone marrow macrophages and within occasional neutrophil and eosinophil granulocytes. Electron microscopy showed the presence of many abnormal cells, which probably represented immature erythroblasts with giant lysosomes. These cells were often large, usually contained immature nuclei with relatively little condensed chromatin, had 1-20 electron dense cytoplasmic granules with an average diameter of 0.5 micron, and regularly displayed substantial rhopheocytotic activity. A few abnormal cells and intermediate and late erythroblasts appeared to have been phagocytosed by macrophages. The data indicate that dyserythropoiesis and ineffective erythropoiesis have a role in the pathogenesis of the anaemia of at least some cases of kala-azar.

A karyometrical study of circulating erythroblasts of yolk sac origin in the mouse embryo

Circulating erythroblasts of embryonic mice were karyometrically examined by light microscopy. In the erythroid cells in embryonic blood vessels, mitoses were encountered from 9 to 12 days of gestation. At 9 days, the circulating blood cells consisted of proerythroblasts and less mature cells. The nuclear diameter ranged from 4.8 to 9.8 micron, the majority ranging between 6 and 8 micron. At 11 days, hemopoietic cells with a nuclear diameter larger than 6 micron disappeared from embryonic circulation, and more than 90% had a nuclear diameter of less than 5 micron. Between 12 and 16 days of gestation, the smallest orthochromatic erythroblasts measuring 3.4 micron nuclear diameter showed the highest peaks. The progress of primitive erythropoiesis in embryonic circulation is discussed in comparison with that of definitive erythropoiesis.

Haemopoietic cells of yolk sac and liver in the mouse embryo: a light and electron microscopical study

Haemopoietic cells in yolk sac and liver of mouse embryo were examined by light and electron microscopy with particular reference to nuclear and nucleolar structure. Mitotic index of yolk sac haemopoietic cells increased from 10 days of gestation, showing a peak at 11 days and, at 12 days, the lumen of the yolk sac vessels were full of erythroblasts with pachychromatic nuclei. In 10 and 11 days yolk sacs, the majority of haemopoietic cells were ultrastructurally large erythroblasts, and, in addition, there were a few extra large erythroblasts and free immature haemopoietic cells. These had reticulated nucleoli and nuclear membrane invagination and were classified as transitional forms between late angioblasts and extra large erythroblasts. After 12 days of gestation, not only these immature cells but extra large erythroblasts disappeared from yolk sac vessels. At 11 days of gestation, hepatic tissues contained haemopoietic cells which were classified as extra large erythroblasts as well as immature cells which resembled late angioblasts on the basis of their nuclear and nucleolar appearance. After 12 days of gestation, erythroblasts showing various stages of maturation appeared and the immature cells remained in the liver until 15 days of gestation. Free haemopoietic cells in the yolk sac and liver are discussed in relation to cells which have the properties of haemopoietic stem cells.

Ultrastructure of sinusoids in patients with agnogenic myeloid metaplasia

Four patients with agnogenic myeloid metaplasia underwent liver biopsies. Under light microscopy, sinusoidal infiltration was very mild or moderate, liver architecture was normal with sinusoids slightly dilated and the perisinusoidal collagen network was increased. Under electron microscopy, in perfusion-fixed sinusoids, the following abnormalities were noticed. a) Presence of hemopoietic cells (erythroid, megakaryocytic, lymphoid, myeloid) at different stages of maturation. More frequently observed in the lumen than in the Disse space, they were usually isolated and never exceeded 2 or 3 cells. In the Disse space, hepatocytes in contact with hemopoietic cells were devoid of microvilli. In the lumen they were close to endothelial cells and Kupffer cells. Kupffer cells were numerous with intense phagocytic activity. b) Numerous collagen bundles encircling sinusoids. c) Transformation of perisinusoidal cells into transitional cells with few lipids, prominent RER, long and thick processes containing filaments sometimes condensed below the plasma membrane. Although only one patient showed clinical evidence of portal hypertension of sinusoidal origin, these results suggest that hepatic vascular resistance might be raised in agnogenic myeloid metaplasia.

A paediatric case of sideroblastic anaemia. Ultrastructural studies of erythroblasts cultured from marrow BFU-E in a methylcellulose micromethod

We examined the morphological and functional characteristics of erythroblasts derived from marrow erythroid progenitor cells grown in a methylcellulose microculture, which were taken from a female child with rare atypical sideroblastic anaemia (SA) partially responsive to pyridoxine. Colony formation was within the normal range in three successive cultures (median values: 82.25 CFU-E and 16.4 BFU-E derived colonies/6.6 X 10(4) cells) compared to growth by normal cells (65-315 CFU-E and 9-40 BFU-E). We evaluated in vitro differentiation by biochemical microassay of a cytosol enzyme involved in the haem pathway: uroporphyrinogen I synthase (UROS). The UROS values in the erythroid colonies from SA marrow were at the lowere end of the normal range (median values: 6.7 +/- 0.3 and 14.4 +/- 3.8 pmol uroporphyrinogen/h in CFU-E and BFU-E-derived colonies respectively versus 17.4 +/- 7.3 and 25 +/- 7.2 pmol/h in CFU-E and BFU-E colonies from normal subjects. Ultrastructural examination of the SA erythroblasts from non-cultured bone marrow or derived from cultured BFU-E revealed the characteristic deposition of iron in mitochondria around the nucleus of most cells (ringed sideroblasts). However, the majority of cultured cells had marked dyserythropoietic features, with a large number of bilobulated or trilobulated erythroblasts, multiple cytoplasmic vacuoles, numerous abnormalities of the nucleus, and excessive membrane material beneath the plasma membrane, all features difficult to observe in non-cultured marrows.

Studies of erythropoietic cells in heterozygotes and homozygotes for haemoglobin Constant Spring and in heterozygotes for both haemoglobin Constant Spring and alpha-thalassaemia 1 trait: extent of globin chain precipitation and cell cycle distribution

Electron microscope studies revealed that the average value for the percentage of erythropoietic cell profiles containing globin chain precipitates in heterozygotes for haemoglobin Constant Spring (HbCS) was similar to that in subjects with alpha-thalassaemia 2 trait and that the average values for this parameter in homozygotes for HbCS and patients with HbCS-H disease were similar to that in individuals with HbH disease. The explanation for the finding that the presence of two alpha cs genes (in homozygotes for HbCS) caused a degree of precipitation corresponding to that seen in patients with HbH disease, who have three deleted alpha genes, rather than to that seen in individuals with alpha-thalassaemia 1 trait, who have two deleted alpha genes, is uncertain. In all the patients with HbCS studied, the majority of the inclusions of precipitated globin chains had a stellate or branching appearance and were considered to consist of beta-chains. However, in the homozygotes for HbCS and to a lesser extent in the patients with HbCS-H disease there were small but significant numbers of erythropoietic cell profiles containing multiple rounded inclusions of the type seen in the beta-thalassaemia syndromes, or both branching and multiple rounded inclusions. It is argued that these rounded inclusions probably consisted either of precipitated HbCS or beta-chains rather than alpha-chains. The distribution of erythroblasts in the different stages of the cell cycle was normal in two homozygotes for HbCS and two patients with HbCS-H disease, indicating that there was little or no cell death during the proliferative phase of erythropoiesis in either of these conditions.

A variant of the congenital dyserythropoietic anaemia type II with structural abnormalities in the granulocytic series

Typical features of congenital dyserythropoietic anaemia (CDA) were found in a 13-year-old girl admitted for chronic recurrent multifocal osteomyelitis. The findings on light microscopy were in agreement with those described in CDA type II, whereas on electron microscopy, the ultrastructure findings were compatible with both types I and II. The acidified serum lysis test (Ham test) performed with eight normal sera was negative. The patient's red blood cells showed an increased agglutinability with anti-i antibodies. Morphological changes were also shown in the mature neutrophilic granulocyte suggesting that the primary disorder exists already in the multipotent stem cell.

Studies of erythroblast function in congenital dyserythropoietic anaemia, type I: evidence of impaired DNA, RNA, and protein synthesis and unbalanced globin chain synthesis in ultrastructurally abnormal cells

Two patients with congenital dyserythropoietic anaemia, type I (CDA) were studied. Their blood reticulocytes showed unbalanced globin chain synthesis with increased alpha:beta globin chain synthesis ratios. A high proportion of the erythroblasts displayed the characteristic "Swiss cheese" abnormality of the nuclear chromatin and some also showed cytoplasmic intrusions lined with nuclear membrane within the nucleus. Occasional erythroblast profiles contained intracytoplasmic inclusions that were ultrastructurally indistinguishable from precipitated alpha chains. The technique of combined Feulgen microspectrophotometry and 3H-thymidine autoradiography showed gross abnormalities of proliferation in the early polychromatic erythroblasts. The proliferative abnormalities included an arrest of DNA synthesis after the progress of cells through part of the S phase and the formation of several mononucleate and binucleate cells with hypertetraploid total DNA contents. The bone marrow cells gave a normal deoxyuridine suppressed value, indicating that there was no impairment of the methylation of deoxyuridylate. Electron microscope autoradiographic studies showed that a high proportion of the erythroblasts with the "Swiss cheese" nuclear abnormality suffered from a severe impairment, or arrest of DNA, RNA, and protein synthesis.

Nuclear bridging of erythroblasts in acquired dyserythropoiesis: an early and transient preleukemic marker

The clinical, hematologic, and histological characteristics of two patients who progressed from refractory anemia to acute leukemia are described. When first studied, nuclear bridging of erythroblasts, similar to that seen in congenital dyserythropoietic anemia type I and megakaryocytic dysplasia, were the only abnormalities. Within 6 years, both patients died, the first of acute nonlymphocytic leukemia, the second of erythroleukemia. Nuclear bridging of erythroblasts in the marrow of these patients was an early and transient phenomenon and was not observed during the terminal phase of leukemia.

A developmentally stable chromatin structure in the human beta-globin gene cluster

The DNase I-hypersensitive sites in the human embryonic beta-globin gene region have been mapped in erythroid-enriched fractions of disaggregated fetal livers, in adult nucleated red blood cells, and in fetal brain tissue. Our analysis of a region extending 11 kilobases (kb) 5' of the epsilon-globin gene reveals many minor nuclease-hypersensitive sites and one major site located 6.1 kb upstream of the epsilon-globin gene. All of these hypersensitive sites are erythroid-specific, and the major site is stable throughout erythroid development. As assayed by nuclear runoff transcription, little or no epsilon-globin gene expression is detectable in fetal or adult erythroid cells. Thus, the presence of the major hypersensitive site 5' of the epsilon-globin gene in both fetal and adult erythroid cells demonstrates that this site is not specifically correlated with transcription of the gene or with a particular stage of development. Rather, this site may reflect an early event in erythroid differentiation. In addition, DNase I has been used to probe the overall sensitivity of epsilon-globin chromatin in fetal erythroid cells. Our findings indicate that the epsilon-globin gene as well as the other genes in the beta-globin cluster reside within the chromatin domain that is more DNase I-sensitive than "bulk" chromatin.

Prosomes. Ubiquity and inter-species structural variation

The "prosomes", a novel type of ubiquitous ribonucleoprotein particle of extraordinary stability and of defined electron microscopical structure, have been characterized in several cell types and species. Identified as a 19 S sub-component of free mRNA-protein complexes, including globin and other repressed mRNA, in the cytoplasm of duck, mouse and HeLa cells, they were previously found to inhibit protein synthesis in vitro. In all cells studied, electron microscopy shows an identical, seemingly ring-like but rather raspberry-shaped particle of 12 nm diameter, resistant to EDTA and 1% (w/v) Sarkosyl. Two-dimensional electrophoretic analysis of prosomal proteins shows a characteristic pattern in the 19,000 to 35,000 Mr range of pI 4 to 7, with an additional 56,000 Mr component specific to avian species. The prosomes found in globin mRNA-protein complexes contain about 25 protein components, 16 of which have identical molecular weight and pI values in duck and mouse, and which are also found in the prosomes of the heterogeneous free mRNPs of HeLa cells. Seral and monoclonal antibodies raised in mice against the prosomes of duck erythroblasts cross-react with some of the proteins of the mouse and HeLa cell particles. Prosomes isolated from duck and mouse globin mRNP, both contain small cytoplasmic RNAs of 70 to 90 nucleotides, which represent about 15% of the particle mass. The molecular weight and the 3'-terminal oligonucleotide of each one of these small cytoplasmic RNAs are identical in the two animal species; fingerprints of their oligonucleotides generated by RNase T1 show that more than 80% of spots are identical. In contrast, the prosomes of HeLa cells, associated with a large population of repressed mRNA, contain at least 12 small cytoplasmic RNA species. All prosomal RNAs tested so far hybridize to mRNA. The data available indicate that prosomes constitute a novel class of ubiquitous cellular ribonucleoprotein complexes, present in the nucleus and cytoplasm that, in its structural variations shown here, reflects function and species.

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.

Erythropoiesis and granulopoiesis in the West Indian manatee, Trichechus manatus (Mammalia: Sirenia)

The West Indian manatee, Trichechus manatus, has amedullary, pachyostotic long bones. Since marrow cavities of the long bones typically are the locations of hemopoiesis in adult mammals, the manatee has evolved an alternative primary site of hemopoiesis. Histological examinations of spleens, livers, kidneys, and vertebral bodies indicate that the last-named location is the main site of erythropoiesis and granulopoiesis in T. manatus. This conclusion is based on the presence in the vertebrae of bone-marrow-containing diagnostic cell types including erythroblasts, megakaryocytes, and myelocytes, which are the precursor cells of erythrocytes, platelets, and granular leukocytes, respectively. No developing lymphocytes were found, so that the location of lymphopoiesis remains unknown.