The role of spatial organization of cells in erythropoiesis.

Erythropoiesis, the process of red blood cell production, occurs mainly in the bone marrow. The functional unit of mammalian erythropoiesis, the erythroblastic island, consists of a central macrophage surrounded by adherent erythroid progenitor cells (CFU-E/Pro-EBs) and their differentiating progeny, the erythroblasts. Central macrophages display on their surface or secrete various growth or inhibitory factors that influence the fate of the surrounding erythroid cells. CFU-E/Pro-EBs have three possible fates: (a) expansion of their numbers without differentiation, (b) differentiation into reticulocytes that are released into the blood, (c) death by apoptosis. CFU-E/Pro-EB fate is under the control of a complex molecular network, that is highly dependent upon environmental conditions in the erythroblastic island. In order to assess the functional role of space coupled with the complex network behavior in erythroblastic islands, we developed hybrid discrete-continuous models of erythropoiesis. A model was developed in which cells are considered as individual physical objects, intracellular regulatory networks are modeled with ordinary differential equations and extracellular concentrations by partial differential equations. We used the model to investigate the impact of an important difference between humans and mice in which mature late-stage erythroblasts produce the most Fas-ligand in humans, whereas early-stage erythroblasts produce the most Fas-ligand in mice. Although the global behaviors of the erythroblastic islands in both species were similar, differences were found, including a relatively slower response time to acute anemia in humans. Also, our modeling approach was very consistent with in vitro culture data, where the central macrophage in reconstituted erythroblastic islands has a strong impact on the dynamics of red blood cell production. The specific spatial organization of erythroblastic islands is key to the normal, stable functioning of mammalian erythropoiesis, both in vitro and in vivo. Our model of a simplified molecular network controlling cell decision provides a realistic functional unit of mammalian erythropoiesis that integrates multiple microenvironmental influences within the erythroblastic island with those of circulating regulators of erythropoiesis, such as EPO and glucocorticosteroids, that are produced at remote sites.

Fus deficiency in mice results in defective B-lymphocyte development and activation, high levels of chromosomal instability and perinatal death.

The gene FUS (also known as TLS (for translocated in liposarcoma) and hnRNP P2) is translocated with the gene encoding the transcription factor ERG-1 in human myeloid leukaemias. Although the functions of wild-type FUS are unknown, the protein contains an RNA-recognition motif and is a component of nuclear riboprotein complexes. FUS resembles a transcription factor in that it binds DNA, contributes a transcriptional activation domain to the FUS-ERG oncoprotein and interacts with several transcription factors in vitro. To better understand FUS function in vivo, we examined the consequences of disrupting Fus in mice. Our results indicate that Fus is essential for viability of neonatal animals, influences lymphocyte development in a non-cell-intrinsic manner, has an intrinsic role in the proliferative responses of B cells to specific mitogenic stimuli and is required for the maintenance of genomic stability. The involvement of a nuclear riboprotein in these processes in vivo indicates that Fus is important in genome maintenance.

Cytoskeletal distribution and function during the maturation and enucleation of mammalian erythroblasts.

We have used murine splenic erythrolasts infected with the anemia-inducing strain of Friend virus (FVA cells), as an in vitro model to study cytoskeletal elements during erythroid maturation and enucleation. FVA cells are capable of enucleating in suspension culture in vitro, indicating that associations with an extracellular matrix or accessory cells are not required for enucleation to occur. The morphology of FVA cells undergoing enucleation is nearly identical to erythroblasts enucleating in vivo. The nucleus is segregated to one side of the cell and then appears to be pinched off resulting in an extruded nucleus and reticulocyte. The extruded nucleus is surrounded by an intact plasma membrane and has little cytoplasm associated with it. Newly formed reticulocytes have an irregular shape, are vacuolated and contain all cytoplasmic organelles. The spatial distribution of several cytoskeletal proteins was examined during the maturation process. Spectrin was found associated with the plasma membrane of FVA cells at all stages of maturation but was segregated entirely to the incipient reticulocyte during enucleation. Microtubules formed cages around nuclei in immature FVA cells and were found primarily in the incipient reticulocyte in cells undergoing enucleation. Reticulocytes occasionally contained microtubules, but a generalized diffuse distribution of tubulin was more common. Vimentin could not be detected at any time in FVA cell maturation. Filamentous actin (F-actin) had a patchy distribution at the cell surface in the most immature erythroblasts, but F-actin bundles could be detected as the cells matured. F-actin was found concentrated between the extruding nucleus and incipient reticulocyte in enucleating erythroblasts. Newly formed reticulocytes exhibited punctate actin fluorescence whereas extruded nuclei lacked F-actin. Addition of colchicine, vinblastine, or taxol to cultures of FVA cells did not affect enucleation. In contrast, cytochalasin D caused a complete inhibition of enucleation that could be reversed by washing out the cytochalasin D. These results demonstrate that F-actin plays a role in enucleation while the complete absence of microtubules or excessive numbers of polymerized microtubules do not affect enucleation.

Erythropoietin retards DNA breakdown and prevents programmed death in erythroid progenitor cells.

The mechanism by which erythropoietin controls mammalian erythrocyte production is unknown. Labeling experiments in vitro with [3H]thymidine demonstrated DNA cleavage in erythroid progenitor cells that was accompanied by DNA repair and synthesis. Erythropoietin reduced DNA cleavage by a factor of 2.6. In the absence of erythropoietin, erythroid progenitor cells accumulated DNA cleavage fragments characteristic of those found in programmed cell death (apoptosis) by 2 to 4 hours and began dying by 16 hours. In the presence of erythropoietin, the progenitor cells survived and differentiated into reticulocytes. Thus, apoptosis is a major component of normal erythropoiesis, and erythropoietin controls erythrocyte production by retarding DNA breakdown and preventing apoptosis in erythroid progenitor cells.

Erythropoietin messenger RNA levels in developing mice and transfer of 125I-erythropoietin by the placenta.

Erythropoietin (EP) mRNA was measured in normal and anemic mice during fetal and postnatal development. Normal fetal livers at 14 d of gestation contained a low level of EP mRNA. By day 19 of gestation, no EP mRNA was detected in normal or anemic fetal livers or normal fetal kidneys, but anemic fetal kidneys had low levels of EP mRNA. Newborn through adult stage mice responded to anemia by accumulating renal and hepatic EP mRNA. However, total liver EP mRNA was considerably less than that of the kidneys. Juvenile animals, 1-4 wk old, were hyperresponsive to anemia in that they produced more EP mRNA than adults. Moreover, nonanemic juveniles had readily measured renal EP mRNA, whereas the adult level was at the lower limit of detection. Because of the very low level of fetal EP mRNA, placental transfer of EP was evaluated. When administered to the pregnant mouse, 125I-EP was transferred in significant amounts to the fetuses. These results indicate that in mice the kidney is the main organ of EP production at all stages of postnatal development and that adult kidney may also play some role in providing EP for fetal erythropoiesis via placental transfer of maternal hormone.

Anemia induces accumulation of erythropoietin mRNA in the kidney and liver.

Regulation of the production of erythropoietin occurs in the kidney and liver largely through control of accumulation of erythropoietin mRNA. Erythropoietin mRNA was first detected in kidneys at 1.5 h postanemia and reached a plateau value at least 200-fold above the control value by 4 to 8 h. A 20-base sequence immediately upstream from the reported erythropoietin mRNA initiation site is complementary to a hypervariable sequence in 18S rRNA.

Control of globin gene transcription by erythropoietin in erythroblasts from friend virus-infected mice.

Splenic erythroblasts of mice infected with the anemia-inducing strain of Friend virus can be isolated in large numbers with less than 5% contamination with other cell types. In short-term culture, the isolated cells will initiate globin synthesis and undergo other aspects of terminal differentiation only if erythropoietin (EP) is added to the medium. An early effect of the hormone on these cells is stimulation of total RNA synthesis. EP also causes initiation of transcription of the beta-globin genes after a lag period of 4 to 6 h. By 6 h, the transcription rate of beta-globin RNA is enhanced threefold, and by 12 h, it is nearly maximal at ca. 20 times the level of control cells which received no EP. Transcription rates of alpha and beta-globin genes are approximately equal to each other throughout the period of terminal differentiation. In the splenic erythroblasts, the chromatin structure in the vicinity of the beta-major globin gene was analyzed with two nucleases during these transcription rate changes. No S1 nuclease-hypersensitive site is detectable near the gene. The beta-major gene is quite sensitive to DNase I in comparison with the albumin gene; however, the level of sensitivity is the same before EP addition as it is during maximal gene transcription after EP addition. Also, a hypersensitive site near the 5' cap site of the beta-major gene is quantitatively equivalent both before and after EP addition. Analysis of cytosine methylation at two sites upstream from the gene showed no changes upon induction of beta-globin gene transcription by EP. Thus, the initiation of beta-globin transcription by EP appears to be at some step after chromatin structural alteration such as synthesis, release, or activation of a specific transcription initiation factor.

Apoptosis in erythroid progenitors deprived of erythropoietin occurs during the G1 and S phases of the cell cycle without growth arrest or stabilization of wild-type p53.

Erythropoietin (Epo) inhibits apoptosis in murine proerythroblasts infected with the anemia-inducing strain of Friend virus (FVA cells). We have shown that the apoptotic process in FVA cell populations deprived of Epo is asynchronous as a result of a heterogeneity in Epo dependence among individual cells. Here we investigated whether apoptosis in FVA cells correlated with cell cycle phase or stabilization of p53 tumor suppressor protein. DNA analysis in nonapoptotic FVA cell subpopulations cultured without Epo demonstrated little change in the percentages of cells in G1,S, and G2/M phases over time. Analysis of the apoptotic subpopulation revealed high percentages of cells in G1 and S, with few cells in G2/M at any time. When cells were sorted from G1 and S phases prior to culture without Epo, apoptotic cells appeared at the same rate in both populations, indicating that no prior commitment step had occurred in either G1 or S phase. Steady-state wild-type p53 protein levels were very low in FVA cells compared with control cell lines and did not accumulate in Epo-deprived cultures; however, p53 protein did accumulate when FVA cells were treated with the DNA-damaging agent actinomycin D. These data indicate that erythroblast apoptosis caused by Epo deprivation (i) occurs throughout G1 and S phases and does not require cell cycle arrest, (ii) does not have a commitment event related to cell cycle phase, and (iii) is not associated with conformational changes or stabilization of wild-type p53 protein.

Chronic myeloid leukemia-associated membranoproliferative glomerulonephritis that responded to imatinib mesylate therapy.

There is no known clinical association between chronic myelogenous leukemia (CML) and membranoproliferative glomerulonephritis (MPGN). We present a patient who was followed in the renal clinic for proteinuria of unknown etiology (3.2 g/24 h) and normal renal function who was diagnosed with CML as well as MPGN and acute renal failure at the same time. The patient's renal function and proteinuria improved when his CML was treated with imatinib mesylate, suggesting that CML either caused or exacerbated existing MGPN. To the best of our knowledge, this is the first reported case of MPGN associated with CML that improved with imatinib mesylate therapy.

Detection of mutations by automated fluorescence/RNA-based dideoxy fingerprinting (ARddF)

Dideoxy fingerprinting (ddF) is a hybrid technique which combines aspects of single strand conformational polymorphism (SSCP) and dideoxy sequencing to detect the presence of single base changes in a defined fragment of nucleic acid. ddF is no more technically demanding than SSCP, yet it is more sensitive in detecting point mutations. We describe here the adaptation of conventional ddF to an automated sequencing system using fluorescent Cy5 labeled primers. We show that automated RNA-based ddF (ARddF) has several advantages over conventional radioisotope-based ddF, including: (1) analysis of larger nucleic acid fragments (up to 10(3) bp), due to the ability to continuously analyse and compile sequencing information; (2) greater reliability for distinguishing mutant sequences from wild type sequences (particularly when the mutation leads to gain or loss of a dideoxy termination segment); (3) the use of fluorescent labeled primers, making ARddF less hazardous than methods requiring radionucleotides. The use of ARddF in conjunction with new methods for isolating RNA from a [corrected] small number of cells facilitates mutational analysis of small tissue biopsies and other limited samples, and will allow more widespread application of mutational screening in the setting of clinical diagnostic laboratories.

Hemolysis caused by factor VIII concentrates.

Immune hemolytic anemia is a recognized complication of the use of factor VIII concentrates. Hemolysis is obscured often by the presence of active bleeding. Where hemolysis has been demonstrated, red blood cell (RBC) destruction has been attributed to anti-A antibodies found in the transfused material. We present two episodes of hemolysis associated with the use of factor VIII concentrate. In the first, a high titer of "immune" anti-A (1:256) was present in the factor VIII. In the second, the patient's RBCs were group B, and the hemolysis was caused by anti-B antibody in the factor VIII concentrate. In addition, the antibody titer in the material that was received was much lower than previously described. The RBC destruction presumably occurred because of the massive dosage of factor VIII concentrate administered on order to overcome a factor VIII inhibitor.

Morphological changes in erythroblasts during erythropoietin-induced terminal differentiation in vitro.

Immature murine erythroblasts infected with the anemia-inducing strain of Friend virus (FVA cells) differentiate in vitro under the influence of erythropoietin (EP). These cells were used as a model for the examination of morphological changes occurring during terminal erythroid differentiation. FVA cells differentiate more completely in vitro in response to EP than continuous erythroleukemia cell lines do in response to chemical induction. Because they can be isolated in much greater numbers and in much higher purity than bone marrow or spleen cells explanted from anemic mice, FVA cells are an attractive alternative for studies of mammalian terminal erythroid differentiation. FVA cells cultured with EP followed a sequence of differentiation events that included a progressive decrease in cell size, disappearance of nucleoli, condensation of nuclei, and accumulation of hemoglobin. After 45 h of culture most FVA cells enucleated, giving rise to vacuolated reticulocytes and free nuclei that were surrounded by a thin layer of cytoplasm and a plasma membrane. The ratio of nuclear to cytoplasmic volumes increased significantly by 24 h of culture but did not change significantly from 24 through 36 h of culture. Variation in the morphology of enucleating FVA cells indicated that not all cells proceeded through a rigorously defined series of morphological stages prior to enucleation. These results are discussed in terms of previous studies of erythroblast maturation.

Plasma S-adenosylhomocysteine is a more sensitive indicator of cardiovascular disease than plasma homocysteine.

BACKGROUND: Although plasma total homocysteine has been identified as an independent risk factor for vascular disease in a multitude of studies, there is a considerable overlap in values between patients at risk and control subjects. The difference in values can be used to distinguish statistically between the 2 groups, provided each group is large enough; however, discriminating between individual patients at risk and control subjects is difficult. OBJECTIVE: We investigated whether the precursor of homocysteine, S-adenosylhomocysteine, is a more sensitive indicator of risk. DESIGN: We measured plasma total homocysteine, S-adenosylhomocysteine, S-adenosylmethionine, creatinine, folate, and vitamin B-12 in 30 patients with proven cardiovascular disease and 29 age- and sex-matched control subjects. RESULTS: The homocysteine values (+/-SD) were 12.8 +/- 4.9 (95% CI: 11.0, 14.7) micromol/L for patients and 11.0 +/- 3.2 (9.8, 12.2) micromol/L for control subjects. The S-adenosylhomocysteine values were 40.0 +/- 20.6 (32.3, 47.7) nmol/L for patients and 27.0 +/- 6.7 (24.5, 30.0) nmol/L for control subjects (P = 0.0021). The S-adenosylmethionine values were 121.8 +/- 42.9 (105.8, 137.8) nmol/L for patients and 103.9 +/- 21.8 (95.6, 112.2) nmol/L for control subjects (P = 0.0493). The creatinine values were 110 +/- 27 (97, 120) micromol/L for patients and 97 +/- 9 (80, 100) micromol/L for control subjects (P = 0.0025). Values for folate and vitamin B-12 did not differ significantly between groups. CONCLUSIONS: Plasma S-adenosylhomocysteine appears to be a much more sensitive indicator of the difference between patients with cardiovascular disease and control subjects than is homocysteine. Both plasma total homocysteine and S-adenosylhomocysteine are significantly correlated with plasma creatinine in patients.

The use of in situ hybridization to study erythropoietin gene expression in murine kidney and liver.

In situ hybridization has been used to localize erythropoietin (EPO)-producing cells in murine kidney and liver. Peritubular interstitial cells were the only cell type that produced EPO in the kidney. The EPO-producing cells were primarily concentrated in the inner cortex but were also seen in the outer medulla and outer cortex. EPO-producing cells represented less than 10% of the total interstitial cell population. The number of EPO-producing cells per square centimeter of cortex directly correlated with the amount of renal EPO mRNA and varied in an inverse exponential manner with hematocrit. These results suggest that EPO is expressed in an all-or-none fashion in peritubular interstitial cells and that the oxygen carrying capacity of blood is the major regulator of renal EPO production. Peritubular interstitial cells were also identified as the renal source of human EPO in transgenic mice that expressed human EPO mRNA is a regulated fashion in the kidney. Transgenic mice exhibiting inducible supranormal liver expression of human EPO were used to identify EPO-producing cells in the liver. Hepatocytes surrounding central veins produced human EPO in these mice. Individual hepatocytes were able to modulate their production of human EPO depending upon the severity of anemia to which they were subjected. Two types of widely scattered cells produced EPO in severely anemic nontransgenic mice. Eighty percent of EPO-producing cells were hepatocytes and 20% were classified as being nonepithelial based on their nuclear morphology and location in venous sinusoids.

A manual therapy approach to evaluation and treatment of a patient with a chronic lumbar nerve root irritation.

The purpose of this case report is to familiarize the reader with the basic principles of the approach to manual therapy evaluation and treatment pioneered by Maitland, an Australian physical therapist. This approach involves a complete subjective examination to determine the severity, irritability, nature, and stage of the patient's complaints. In this way, the therapist may reach conclusions as to the amount and vigor of the physical examination and proceed with treatment in an analytical manner. Methodical reassessment is used to justify treatment progression. Comprehensive treatment and the rationale for this approach are discussed. Though most physical therapists are familiar with the straight-leg-raising test as a means of assessing low back pain and chronic lumbar nerve root irritation, they are often not familiar with other tests that examine neural tissues, such as the slump test. The proposed anatomical and biomechanical bases for these tests are discussed. The patient in this case study was a 50-year-old man with a physician's diagnosis of a chronic lumbar nerve root irritation. The patient was evaluated and treated in eight visits using techniques designed to evaluate neural tissues. Reassessment indicated significant symptom reduction, and the treatment was modified accordingly. Patient management, including home exercises, is discussed.

Needle aspiration and biopsy in the diagnosis and monitoring of bone marrow diseases.

OBJECTIVE: To review the procedures required to perform and evaluate needle aspiration and biopsy of bone marrow. DATA SOURCES: Journal articles, monographs and authors' experience. DATA SYNTHESIS: The performance of bone marrow needle aspiration and biopsy requires close cooperation between the physician and the clinical laboratory scientist (CLS). Several tests require special handling when obtaining and processing bone marrow samples. Serial bone marrow aspiration and biopsy studies can help in the management of some bone marrow diseases. This article reviews the procedures required to obtain and to process bone marrow aspirates and biopsies. It also reviews the interpretation of light microscopic studies of bone marrow samples. CONCLUSION: Current procedures for obtaining and procuring bone marrow needle aspirates and biopsies require close interaction between the CLS and the physician. Multiple specialized assays require special handling at the time marrow samples are obtained. Serial bone marrow needle aspirates and biopsies can be very useful in guiding the clinical care of certain patients.