Human globin chain separation by isoelectric focusing

Molecular diagnosis of inherited disorders: lessons from hemoglobinopathies

Hemoglobinopathies constitute a major health problem worldwide, with a high carrier frequency, particularly in certain regions where malaria has been endemic. These disorders are characterized by a vast clinical and hematological phenotypic heterogeneity. Over 1,200 different genetic alterations that affect the DNA sequence of the human alpha-like (HBZ, HBA2, HBA1, and HBQ1) and beta-like (HBE1, HBG2, HBG1, HBD, and HBB) globin genes are mainly responsible for the observed clinical heterogeneity. These mutations, together with detailed information about the resulting phenotype, are documented in the globin locus-specific HbVar database. Family studies and comprehensive hematological analyses provide useful insights for accurately diagnosing thalassemia at the DNA level. For this purpose, numerous techniques can provide accurate, rapid, and cost-effective identification of the underlying genetic defect in affected individuals. The aim of this article is to review the diverse methodological and technical platforms available for the molecular diagnosis of inherited disorders, using thalassemia and hemoglobinopathies as a model. This article also attempts to shed light on issues closely related to thalassemia diagnostics, such as prenatal and preimplantation genetic diagnoses and genetic counseling, for better-quality disease management.

Capillary electrophoretic analysis of proteins and peptides of biomedical and pharmacological interest

Capillary electrophoresis (CE) is an automated approach to electrokinetic separations that has had a deep impact in all fields of life sciences, including biomedical and biotechnological research and clinical and forensic practice. The present review highlights aspects of peptides and proteins separations, with particular emphasis on macromolecular analytes of biomedical interest. Among the various CE techniques available, a novel methodology is here illustrated consisting in separations in acidic, isoelectric buffers, which have the advantage of protonating the silica wall, thus minimizing interactions of proteinaceous material with the siliceous surface, while allowing delivery of high voltage gradients, due to their low conductivities. The review ends with applications of CE to the analysis of folding/unfolding/refolding/misfolding of proteins, a field which has deep implications in the biomedical arena, since it is connected to a host of disorders, such as prion protein diseases.

Capillary electrophoresis of peptides and proteins in acidic, isoelectric buffers: recent developments

The use of isoelectric buffers in capillary zone electrophoresis is here reviewed. Such buffers allow delivery of very high voltage gradients (up to 1000 V/cm in relatively large bore capillaries, e.g. 75-100 microm I.D.), permitting separations of the order of a few minutes and thus conserving (in fact favouring) very high resolution due to minimal, diffusion-driven, peak spreading. Isoelectric Asp (pI 2.77 at 50 mM concentration and 25 degrees C) provides a medium of high resolving power for generating peptide maps. In difficult cases, of coincident titration curves, the pH can be moved up to higher values (e.g. pH 3.0 for 30 mM Asp) thus eliciting separation of unresolved peptides at pH 2.77. This was illustrated by running peptide maps of tryptic digests of human beta globin chains. Also imino diacetic acid (pI 2.33 at 50 mM concentration) allows generation of high resolution peptide maps. Isoelectric Asp, in presence of 7 M urea and 0.5% hydroxyethyl cellulose (Mn = 27 000 Da) is also the preferred medium for fast separation and analysis of storage proteins in cereals, such as gliadins in soft and durum wheat and zeins in maize. A solution of 50 mM iminodiacetic acid (pI 2.23) containing 7 M urea and 0.5% hydroxyethylcellulose (apparent pH 3.2) is effectively used as background electrolyte for fast separation of heme-free, denatured globin (alpha and beta) chains. In the presence of neutral to neutral amino acid substitutions, it is additionally shown that the inclusion of 3% surfactant (Tween 20) in the sample and background electrolyte induces the separation of the wild-type and mutant chains, probably by a mechanism of hydrophobic interaction of the more hydrophobic mutant with the detergent micelle, via a mechanism similar to 'micellar electrokinetic chromatography'.

Detection of neutral and charged mutations in alpha- and beta-human globin chains by capillary zone electrophoresis in isoelectric, acidic buffers

A simple and reliable method, for screening for point mutations in alpha- and beta-human globin chains, is reported here, utilizing capillary zone electrophoresis in isoelectric, acidic buffers. A solution of 50 mM iminodiacetic acid (pI 2.23) containing 7 M urea and 0.5% hydroxyethylcellulose (apparent pH 3.2) is used as background electrolyte for fast separation of heme-free, denatured globin (alpha and beta) chains. Due to the low conductivity of such buffers, high voltage gradients (600 V/cm) can be applied, thus reducing the separation time to only a few minutes. In presence of neutral to neutral amino acid substitutions, it is additionally shown that the inclusion of 3% surfactant (Tween 20) in the sample and background electrolyte induces the separation of the wild-type and mutant chains, probably by a mechanism of hydrophobic interaction of the more hydrophobic mutant with the detergent micelle, via a mechanism similar to "micellar electrokinetic chromatography". At this low operative pH, however, charged mutants, involving substitutions of acidic amino acids (Glu and Asp) are not detected, since these residues are extensively protonated. Curiously, however, they are still separated in presence of detergent, due to the large variation in hydrophobicity involved in such mutations. Of the 19 mutants analyzed, all but one were resolved: Hb St Nazaire (beta 103 Phe-->Ile). This is due to the fact that the delta G (in kcal/mol) in the substitution Phe-->Ile is zero, thus no separation can possibly take place between two chains exhibiting the same hydrophobicity parameter.

Globin chain synthesis analysis by high performance liquid chromatography in the screening of thalassemia syndromes

We applied reversed phase high performance liquid chromatography for globin chain synthesis analysis in screening for beta-thalassemia. The alpha/non-alpha-globin chain synthesis ratios have been determined in alpha-, beta-, and deltabeta-thalassemia carriers using the classical carboxymethyl cellulose chromatography as the reference method. Reversed phase high performance liquid chromatography is fast, accurate, and reproducible, and may be a suitable alternative for the traditional carboxymethyl cellulose chromatography.

Human globin chain separation by capillary electrophoresis in acidic isoelectric buffers

A simple and reliable method, utilizing capillary electrophoresis in uncoated capillaries in acidic isoelectric buffers, is reported for screening for thalassemia and other defects on the synthesis of human globin chains. A solution of 50 mM iminodiacetic acid (pI 2.23), containing 7 M urea and 0.5% hydroxyethylcellulose (apparent pH 3.2) is used as background electrolyte for fast separation of heme-free, denatured globin (alpha, beta and gamma) chains. Due to the low conductivity of such a buffer, high voltage gradients (600 V/cm) can be applied, thus reducing the separation time to only a few minutes. It is additionally shown that inclusion of 2% surfactant (Tween 20) in the background electrolyte induces the splitting of the gamma chains into two zones, called Agamma and Ggamma, which represent the products of two genes coding for Ala or Gly as residue 136 of the chain.

Screening of umbilical cord blood hemoglobins by isoelectric focusing in capillaries

Separation and quantitation of the three main hemoglobin components of umbilical cord blood (fetal, acetylated fetal and adult hemoglobins; Hb F, Fac, A) by capillary isoelectric focusing (IEF) in a pH 6-8 gradient is reported. Even in coated capillaries (with covalently bound chains of linear acrylamido derivatives, notably N-acryloylaminoethoxyethanol), no base line separation is obtained between Hb F and A, although this is routinely achieved in gel slab IEF. However, when the carrier ampholyte buffers were added to 3% short-chain liquid linear polyacrylamide, base line resolution and stabilization of peak transit times were obtained. This suggests that even in the best coating procedures, patches of the inner capillary surface could still be naked, so that the static coating is complemented by a dynamic coating on the unoccupied sites. An additional improvement in separation occurs if the above mixture, comprising 5% carrier ampholytes in the pH 6-8 range and 3% soluble polyacrylamide, is made to contain 50 mM beta-alanine, a "separator" known to flatten the pH gradient around pH 7. In the normal newborns analyzed (n = 30), the following average values were obtained: Hb F, 70.1% (range 65-75%); Hb A, 20.2% (range 15-25%); and HbFac, 9.5% (range 7-11%).

Isoelectric focusing as a tool for the investigation of post-translational processing and chemical modifications of proteins

It has been demonstrated that good agreement may be observed between computed and experimental isoelectric point (pI) values when proteins of known sequence are focused under denaturing conditions on immobilized pH gradient IPG slabs, at least in the pH range 4-7.5. Hence, discrepancies between expected and found in this experimental set-up may be reliably ascribed to some kind of post-transcriptional processing, or chemical modification, having taken place in the sample. This evaluation is made easier when the comparison is set between the pI of a parent molecule and that (or those) of one to several of its derivatives as resolved in a single experiment (for instance, as a spot row in two-dimensional maps); no previous knowledge is required in these cases about the amino acid composition of the primary structure. The effects on protein surface charge are discussed in this review mainly for two biologically relevant processes, glycosylation and phosphorylation. Then, the pI shifts are analysed for some protein modifications that may occur naturally but can also be artefactually elicited, such as NH2 terminus blocking, deamidation and thiol redox reactions. Finally, carboxymethylation and carbamylation are used to exemplify chemical treatments often applied in connection with electrophoretic techniques and involving charged residues. Procedures to be applied in order to verify whether a given modification has occurred, and often relying on the focusing of a treated specimen, are detailed in each section. Numerical examples on model proteins are also discussed. As an important field of application of the above concepts may be genetic engineering, an exhaustive bibliographic list dealing with pI evaluation and structural assessment on recombinant proteins is included.

Hematopoietic commitment during embryonic stem cell differentiation in culture

We report that embryonic stem cells efficiently undergo differentiation in vitro to mesoderm and hematopoietic cells and that this in vitro system recapitulates days 6.5 to 7.5 of mouse hematopoietic development. Embryonic stem cells differentiated as embryoid bodies (EBs) develop erythroid precursors by day 4 of differentiation, and by day 6, more than 85% of EBs contain such cells. A comparative reverse transcriptase-mediated polymerase chain reaction profile of marker genes for primitive endoderm (collagen alpha IV) and mesoderm (Brachyury) indicates that both cell types are present in the developing EBs as well in normal embryos prior to the onset of hematopoiesis. GATA-1, GATA-3, and vav are expressed in both the EBs and embryos just prior to and/or during the early onset of hematopoiesis, indicating that they could play a role in the early stages of hematopoietic development both in vivo and in vitro. The initial stages of hematopoietic development within the EBs occur in the absence of added growth factors and are not significantly influenced by the addition of a broad spectrum of factors, including interleukin-3 (IL-3), IL-1, IL-6, IL-11, erythropoietin, and Kit ligand. At days 10 and 14 of differentiation, EB hematopoiesis is significantly enhanced by the addition of both Kit ligand and IL-11 to the cultures. Kinetic analysis indicates that hematopoietic precursors develop within the EBs in an ordered pattern. Precursors of the primitive erythroid lineage appear first, approximately 24 h before precursors of the macrophage and definitive erythroid lineages. Bipotential neutrophil/macrophage and multilineage precursors appear next, and precursors of the mast cell lineage develop last. The kinetics of precursor development, as well as the growth factor responsiveness of these early cells, is similar to that found in the yolk sac and early fetal liver, indicating that the onset of hematopoiesis within the EBs parallels that found in the embryo.

Hematopoietic commitment during embryonic stem cell differentiation in culture

We report that embryonic stem cells efficiently undergo differentiation in vitro to mesoderm and hematopoietic cells and that this in vitro system recapitulates days 6.5 to 7.5 of mouse hematopoietic development. Embryonic stem cells differentiated as embryoid bodies (EBs) develop erythroid precursors by day 4 of differentiation, and by day 6, more than 85% of EBs contain such cells. A comparative reverse transcriptase-mediated polymerase chain reaction profile of marker genes for primitive endoderm (collagen alpha IV) and mesoderm (Brachyury) indicates that both cell types are present in the developing EBs as well in normal embryos prior to the onset of hematopoiesis. GATA-1, GATA-3, and vav are expressed in both the EBs and embryos just prior to and/or during the early onset of hematopoiesis, indicating that they could play a role in the early stages of hematopoietic development both in vivo and in vitro. The initial stages of hematopoietic development within the EBs occur in the absence of added growth factors and are not significantly influenced by the addition of a broad spectrum of factors, including interleukin-3 (IL-3), IL-1, IL-6, IL-11, erythropoietin, and Kit ligand. At days 10 and 14 of differentiation, EB hematopoiesis is significantly enhanced by the addition of both Kit ligand and IL-11 to the cultures. Kinetic analysis indicates that hematopoietic precursors develop within the EBs in an ordered pattern. Precursors of the primitive erythroid lineage appear first, approximately 24 h before precursors of the macrophage and definitive erythroid lineages. Bipotential neutrophil/macrophage and multilineage precursors appear next, and precursors of the mast cell lineage develop last. The kinetics of precursor development, as well as the growth factor responsiveness of these early cells, is similar to that found in the yolk sac and early fetal liver, indicating that the onset of hematopoiesis within the EBs parallels that found in the embryo.

Isoelectric focusing in immobilized pH gradients: applications in clinical chemistry and forensic analysis

The applications of isoelectric focusing in immobilized pH gradients in clinical chemistry and forensic analysis are reviewed. Strong emphasis is given to the separation of serum proteins, in particular alpha 1-acidic glycoprotein, acid phosphatase, alkaline phosphatase, alpha 1-antitrypsin, apolipoproteins, complement component, factor B, factor XIIIB, group-specific component, lecithin:cholesterol acyltransferase, phosphoglucomutase, prealbumin, protein C and transferrin. The analysis of human parotid salivary proteins is discussed and an assessment is given of the state of the art in thalassaemia screening.

In utero transplantation of hematopoietic stem cells in sheep: the role of T cells in engraftment and graft-versus-host disease

Transplantation of hematopoietic stem cells (HSC) from adult sheep into fetal lambs results in hematopoietic chimerism and graft-versus-host disease (GVHD). To evaluate the role of T cells in HSC engraftment and GVHD we depleted adult marrow HSC of T cells and observed the incidence of chimerism and GVHD in the fetal recipients. Using a naturally occurring polymorphism of the beta-globin locus to detect engraftment, bone marrow obtained from homozygous type A hemoglobin adult sheep were transplanted (2 x 10(9) cells/kg fetal weight) into 90 days' gestation fetal lambs homozygous for type B hemoglobin. Donor HSC were T-cell depleted by treatment with antisera (raised in rabbits against sheep thymocytes) in the presence of complement. T-cell depletion resulted in significant decrease in hematopoietic colony formation by donor HSC in vitro (305 +/- 49 v 134 +/- 21 colonies/10(5) cells) that normalized by the addition of autologous T cells (433 +/- 32 colonies/10(5) cells). Marrow depleted of T cells exhibited reduced engraftment in the recipient fetuses. When T cells were added back to donor HSC (depleted of T cells) at near-normal concentrations, engraftment improved but the lambs also developed GVHD. The addition of T cells to donor HSC (depleted of T cells) at concentrations below that present in unprocessed bone marrow resulted in significant engraftment but not GVHD. T cells play an important role in both the engraftment of adult HSC in fetal recipients and the development of GVHD in chimeric newborns. The elimination of T cells prevents GVHD but markedly reduces engraftment.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythropoiesis following bone marrow transplantation from donors heterozygous for beta-thalassaemia

This study shows a marked and protracted activation of HbF synthesis in homozygous beta.-thalassaemia patients transplanted from HLA identical siblings heterozygous for beta-thalassaemia, as compared to patients transplanted from normal donors. HbF synthesis in recipients was much higher in relation to the corresponding bone marrow donor values either normal or heterozygous for beta thalassaemia. gamma-chain synthesis and G gamma/A gamma ratio were also studied in peripheral blood BFU-E from recipients and their donors. BFU-E from donors heterozygous for beta-thalassaemia showed higher gamma chain synthesis as compared to normal donors. Peripheral blood BFU-E gamma/beta + gamma ratios and G gamma percentage were higher in recipients than in their corresponding donors both normal or heterozygotes. The marked and protracted reactivation of HbF synthesis in recipients of heterozygous beta-thalassaemia bone marrow most likely results from an increased erythropoietic stress on erythroid progenitors. In order to obtain adequate Hb levels heterozygous beta-thalassaemia bone marrow should produce more red blood cells to compensate for the low MCH. The magnitude of activation of HbF synthesis was very variable. This variability may result from inherited differences in the capacity of reactivation of HbF synthesis of red cell progenitors from heterozygous beta-thalassaemia under stressed erythropoiesis.

Rapid HPLC techniques for globin chain synthesis studies

Globin chain synthesis and alpha/beta ratios were determined in a number of normal subjects, alpha-thalassemia-2 homozygotes, and beta-thalassemia trait using three different techniques. Cation exchange high performance liquid chromatography on a Pharmacia Mono-S, HR 5/5 and reversed phase high performance liquid chromatography on a semi-preparative Vydac C4 column were compared with the traditional carboxymethylcellulose chromatography. Both high performance liquid chromatography columns give excellent results when 2 mg of hemoglobin was chromatographed in each analysis. By modifying the protocols for column equilibration and gradient shape for preparative Vydac C4 columns, conditions were found yielding excellent resolutions of the labeled globin chains in less than an hour without the need for substantial increase of the flowrate. This method was found to be superior to other methods and may be a suitable alternative for the classical carboxymethylcellulose chromatography. Up to five specimens could easily be analyzed in a single day with this system.

Erythropoietin changes the globin program of an interleukin 3-dependent multipotential cell line

B6SUtA is a factor-dependent murine cell line of adult origin displaying the functional properties of a multipotent hematopoietic stem cell. We analyzed the globin programs of B6SUtA cells undergoing erythroid differentiation in both suspension and clonal cultures. In the absence of added erythropoietin, a small number of hemoglobinized cells were present, and these expressed predominantly embryonic globin. Addition of erythropoietin increased the number and maturation of hemoglobinized cells and led to a preferential augmentation of adult globin. Analysis of individual B6SUtA erythroid bursts showed that embryonic and adult globin can be expressed in cells derived from a single progenitor. Furthermore, by studying globin expression in cultured cells from mouse embryos, we found that the globin programs of B6SUtA cells are similar to those of erythroid progenitors at the period of transition from yolk sac to fetal liver erythropoiesis. Since B6SUtA cells are derived from adult bone marrow and they have the capacity to express embryonic globin, we speculate that the globin locus is not irreversibly modified during development and that adult cells at early stages of erythroid differentiation can transiently express ontogenetically primitive globin programs.

Hemoglobin Tilburg: alpha 2-beta 2 73 (E 17) Asp----Gly. A new hemoglobin with reduced oxygen affinity

A new hemoglobin variant has been found in a Dutch Caucasian girl and detected also in members of three generations of her family. This variant is characterized by the substitution of an aspartic acid at position 73 (E 17) of the beta-chain with a glycine residue. Hemoglobin Tilburg makes up to 42% of the total hemoglobin in the blood of the proposita, it is stable at the isopropanol test, and not associated with significant hematological abnormalities in heterozygous carriers. The oxygen dissociation curve of the purified variant, carried out at different pH values, shows a definite reduction of the affinity for oxygen and a normal alkaline Bohr effect. Three more hemoglobins with a single amino acid substitution at the same site have been previously described: Hb Korle-Bu (Asp----Asn), Hb Mobile (Asp----Val) and Hb Vancouver (Asp----Tyr). In all these proteins the affinity for oxygen is lowered to an extent which is variable and characteristic of each mutant. In this paper we discuss the possible mechanism responsible for the abnormal behaviour of hemoglobins substituted at beta 73.

Mechanism of Hb F stimulation by S-stage compounds. In vitro studies with bone marrow cells exposed to 5-azacytidine, Ara-C, or hydroxyurea

The in vitro effect of S-stage-specific drugs on the fetal hemoglobin (Hb F) potential of erythroid precursors and progenitors was tested by exposing bone marrow cells to 5-aza-2'-deoxycytidine, Ara-C, or hydroxyurea in suspension cultures and reculturing the cells in drug-free clonal cultures. Analysis of Hb F in the erythroblasts present at the end of suspension cultures and in the erythroid colonies formed from treated progenitors showed that 1 X 10(-9)-5 X 10(-8) M 5-aza-2'-deoxycytidine produced a concentration-related increase in the proportion of Hb F-positive erythroblasts, of Hb F-positive erythroid CFU (CFUe) colonies, and at the higher doses used, an increased Hb F expression in erythroid burst-forming unit (BFUe)-derived colonies. Preincubation of bone marrow cells with Ara-C produced significant megaloblastic changes by the end of the 2-d incubation and increased the proportion of Hb F-positive erythroblasts, CFUe colonies, and e-clusters, but BFUe-derived progeny was unaffected. Hydroxyurea failed to produce significant changes in Hb F at the range of concentrations used. The data raise the possibility of more than one mechanism underlying the stimulation of Hb F by S-stage drugs.

Identification by fast atom bombardment mass spectrometry of Hb Indianapolis [beta 112(G14)Cys----Arg] in a family from Naples, Italy

We have characterized a beta 112 Arg hemoglobin in an individual from Naples, Italy, with minimal clinical problems. Blood tests revealed only slight reticulocytosis and hemoglobin instability. Furthermore, high value of alkali resistance tests for Hb F were observed. Isoelectricfocusing of globins showed the occurrence of a band migrating between the normal alpha and beta globin chains. The fairly stable variant chain was purified by fast protein liquid chromatography. A mass map of the tryptic digest was obtained by fast atom bombardment mass spectrometry clearly showing that we were dealing with a beta chain variant. However, the peptide 105-120 was missing and two new ones were present, i.e.: 105-112 and 113-120; we assumed these peptides to be generated because of the substitution of 112 Cys with an arginine residue. Further confirmation stemmed from the fast atom bombardment mass spectra of the tryptic digest submitted to a single Edman degradation step and to carboxypeptidase B further hydrolysis. The beta-globin chain variant was thus mass mapped to an extent of about 98%. Such a variant, named Hb Indianapolis, was first reported by Adams et al, as an extremely unstable variant producing the phenotype of a severe beta-thalassemia. Contrary to the findings of the above authors the occurrence of the same variant in a clinically normal individual from a Spanish family has recently been reported. Because the clinical manifestations in the latter case are similar to those observed by us, the conclusion can be drawn that beta 112 Arg hemoglobin is not a biologically unstable variant but should be regarded as belonging to the class of unstable hemoglobins giving rise to only marginal clinical problems.

Coexpression of embryonic, fetal, and adult globins in erythroid cells of human embryos: relevance to the cell-lineage models of globin switching

The cellular control of the switch from embryonic to fetal globin formation in man was investigated with studies of globin expression in erythroid cells of 35- to 56-day-old embryos. Analyses of globins synthesized in vivo and in cultures of erythroid progenitors (burst-forming units, BFUe) showed that cells of the yolk sac (primitive) erythropoiesis, in addition to embryonic chains, produced fetal and adult globins and that cells of the definitive (liver) erythropoiesis, in addition to fetal and adult globins, produce embryonic globins. That embryonic, fetal, and adult globins were coexpressed by cells of the same lineage was documented by analysis of globin chains in single BFUe colonies: all 67 yolk sac-origin BFUe colonies and 42 of 43 liver-origin BFUe colonies synthesized epsilon-, gamma-, and beta-chains. These data showed that during the switch from embryonic to adult globin formation, embryonic and definitive globin chains are coexpressed in the primitive, as well as in the definitive, erythroid cells. Such results are compatible with the postulate that the switch from embryonic to fetal globin synthesis represents a time-dependent change in programs of progenitor cells rather than a change in hemopoietic cell lineages.

Stimulation of fetal hemoglobin synthesis by erythropoietin in baboons

Stimulating the production of fetal hemoglobin may benefit patients with sickle cell anemia by inhibiting sickling. We gave pulsed treatments with high doses of recombinant human erythropoietin to baboons in order to test the hypothesis that the resultant rapid erythroid regeneration would stimulate F cells--i.e., cells that contain fetal hemoglobin. In normal animals, this treatment caused sharp increments in F-reticulocyte levels, which rose from 1 to 2 percent before treatment to 40 to 50 percent afterward. In two animals with chronic anemia and high levels of endogenous erythropoietin, recombinant human erythropoietin induced further increments in F-reticulocyte levels, which rose in one animal from 6 to 8 percent before treatment to 23 percent after treatment, and in the other from 20 percent before to 50 percent afterward. The time course of F-reticulocyte stimulation suggested that these cells were the products of mobilized early erythroid progenitors. These results raise the possibility that pulses of erythropoietin could be used to stimulate F-cell formation in patients with sickle cell disease.

Resolution of G gamma and A gamma foetal haemoglobin tetramers in immobilized pH gradients

Intact tetramers of foetal haemoglobin (G gamma, A gamma and the mutant A gamma T) can be separated by isoelectric focusing in immobilized pH gradients over a very shallow pH interval (pH 7.35-7.55). The G gamma tetramer exhibits a lower pI (7.450) than the A gamma tetramer (pI 7.453); the delta pI between the two species is barely 0.003 of a pH unit, close to the theoretical resolution limit of the technique, delta pI = 0.001. Haem-free, denatured gamma chains exhibit a reversal in pI order, the A gamma chain being more acidic than the G gamma chains: this is attributed to preferential binding of detergent micelles to the more hydrophobic A gamma polypeptide. The advantage of the present technique is the simultaneous analysis of several samples (30-40 per gel slab) and the recovery of intact, haemoglobin tetramers for subsequent studies.

Transplantation of fetal hematopoietic stem cells in utero: the creation of hematopoietic chimeras

Transplantation of normal, immature, fetal hematopoietic cells into a preimmune fetal recipient with a congenital hemoglobinopathy may allow partial reconstitution of normal hemoglobin production without the complications associated with postnatal bone marrow transplantation (immunosuppression and the occurrence of graft versus host disease). In order to test this hypothesis the naturally occurring polymorphism at the beta-hemoglobin locus of the sheep was used as a marker for engraftment and hematopoietic chimerism. Intraperitoneal injection of allogeneic fetal stem cells into normal fetal lambs resulted in hematopoietic chimerism in three of four surviving recipients. This chimerism has been sustained for 6 months after birth and 9 months after engraftment, without evidence of graft versus host disease, and without the use of immunosuppressive therapy.

Analysis of human hemoglobin switching in MEL x human fetal erythroid cell hybrids

The switch from fetal to adult globin synthesis in man was studied using heterospecific cell hybrids between human fetal erythroblasts and mouse erythroleukemia cells. When erythroblasts from first trimester fetuses were used the hybrids expressed a fetal program of human globin expression. While in continuous culture, these hybrids switched from predominantly fetal to almost exclusively adult globin expression, providing direct evidence that switching can occur within a single cell lineage. Sequential studies of globin expression at a single cell level and subcloning experiments suggested that the switch reflects a progressive increase in the generation of beta + cells from gamma + cells. Hybrids formed with erythroblasts of second trimester fetuses switched faster than those produced with cells of first trimester fetuses. The findings suggest that the human gamma to beta switch is controlled by a developmental clock-like mechanism, which appears to be associated with chromosome 11.

Antenatal diagnosis of beta-thalassemia by isoelectric focusing in immobilized ph gradients

A new method for antenatal diagnosis of thalassemias is reported based on the analysis of the major Hb components of fetal cord blood, sampled at week 18 of pregnancy under ultrasonic guidance, by isoelectric focusing in immobilized pH gradients (IPG). In an IPG gel encompassing a pH 6.7-7.6 span, HbA and HbFac are separated by a distance nine times greater than in a conventional carrier ampholyte pH 6-8 gel and three times greater than in an ampholine gel with separators (an equimolar mixture of beta-alanine and 6-amino caproic acid). Band evenness (in terms of uniform protein concentration within a zone) and straightness (in terms of parallel alignment of the bands to the electrodes), because of insensitivity of IPG gels to salt distortions, allows for accurate and reproducible quantitation of HbF, -A, and -Fac levels. The possibility of greatly overloading IPG matrices in total Hbs increases the sensitivity of the technique to the detection of only 0.5% HbA in the total Hb mixture, the lower limit of conventional IEF being only 2.5% HbA. Of 15 fetuses from couples at risk analyzed in the region of Ozieri, three were found to be homozygous beta-thalassemic, eight heterozygous, and four normal with no false-positives or -negatives.

Detection of electrophoretically silent mutations by immobilized pH gradients

The detection of neutral amino acid mutants, by isoelectric focusing in immobilized pH gradients (IPGs), is exemplified by the separation of hemoglobin (Hb) Beirut (126 beta Val----Ala) from Hb A in a shallow pH 7.2-7.6 IPG gradient with 2% Ampholine pH 6-8. The mechanism of these separations appears to involve minute alterations in the pK values of ionizable groups bordering the mutation site, which are in turn reflected in tiny alterations in the net surface charge, delta pI. The delta pI values are of the order of 0.01 to 0.001 pH units, outside the resolving limits of conventional isoelectric focusing, and correspond to changes of the order of 0.1-0.01 unit charge (a proton or an electron).

Reversed-phase high-performance liquid chromatography of human haemoglobin chains

A reversed-phase high-performance liquid chromatographic method for the separation of human haemoglobin chains has been devised. Using a LiChrospher 100 CH-8/2 column and a ternary eluent (acetonitrile-methanol-0.155 M NaCl, pH 2.7) improved resolution was achieved between (delta beta) Lepore, beta A, beta S, alpha, G gamma and A gamma chains within a 60-min linear gradient. The A gamma T chain can also be separated by increasing the gradient time and decreasing the flow-rate. Silanophilic interactions play an important role in the retention mechanism, and NaCl addition was necessary in order to suppress adsorption on free silanols. Increasing the methanol concentration to 10% caused a slight increase in chain retention, probably owing to solvation of the stationary phase. The recovery was 82% and the reproducibility of retention times was as good as +/- 1.5%. Quantitation of chains is likely to be possible by peak area measurement. Owing to its sensitivity, the proposed method may be useful in the diagnosis of haemoglobinopathies and in the study of haemoglobin variants.

Adult and fetal human globin genes are expressed following chromosomal transfer into MEL cells

Somatic cell hybridization of mouse erythroleukemia (MEL) cells and HEL cells, a human erythroleukemia line that produces fetal (gamma) but fails to express adult (beta) globin, was used to test whether the expression of the two human globin genes is regulated cis or trans. An experimental approach using anti-human globin monoclonal antibodies for detection, efficient cloning, and monitoring of hybrids of interest was employed. Further characterization of hybrids used isoelectric focusing for detection of human globins and S1 nuclease mapping. In contrast to the parental HEL line, all chromosome 11-retaining HEL-MEL hybrids expressed human beta-globin, suggesting that the HEL beta-globin genes (i) are transcriptionally competent, (ii) become activated in response to a positive trans-acting element within the MEL environment, and (iii) fail to express into the HEL environment because of either the absence of a positive trans-acting element or the presence of a trans-acting inhibitor of beta-globin gene expression. In addition to beta-globin, the primary HEL-MEL hybrids co-expressed gamma-globin; however, gamma-globin expression segregated by subcloning so that secondary and tertiary clones either expressed only beta-globin or co-expressed gamma- and beta-globin. The results of subcloning can be explained by assuming that gamma-globin gene expression is controlled by a HEL cell-derived transacting element encoded by a gene not syntenic to chromosome 11 or by postulating that the HEL gamma-globin genes become randomly modified during the continuous proliferation of hybrids.

Isoelectric focusing and two-dimensional electrophoresis of tubulin using immobilized pH gradients under denaturing conditions

Modifications of the LKB Immobiline isoelectric focusing (IEF) technique are described for use under conditions that solubilize and denature most proteins (8 M urea and 2% Nonidet-P40). This procedure permits pH gradients that are four- to fivefold shallower than previously available with conventional ampholine-IEF procedures. It can also be used as a first dimension in two-dimensional gel electrophoresis. The advantage of the stable ultranarrow pH gradient is demonstrated by directly comparing the resolution of vertebrate brain tubulins using (i) denaturing conventional ampholine-IEF and (ii) denaturing Immobiline-IEF. Analysis of tubulin on the Immobiline-IEF gel increases the separation distance between the individual tubulins and distinguishes differences among tubulin samples that could not be resolved by conventional ampholine isoelectric focusing.

A haemoglobin switching activity modulates hereditary persistence of fetal haemoglobin

During human development there is a switch from fetal to adult haemoglobin formation, reflecting the differential expression of fetal (G gamma and A gamma) and adult (beta and delta) globin genes. Mutations that inhibit this switch produce variants of the syndrome of hereditary persistence of fetal haemoglobin (HPFH). Adult heterozygotes for these mutants produce 15-30% fetal haemoglobin (HbF) in their red cells. The general assumption is that the mutations result in a permanent switching on of gamma-globin genes. Here, however, we show that fetal globin expression can be turned off in cultures of HPFH cells by an uncharacterized factor in fetal sheep serum. This is the first demonstration that mutations affecting the developmental expression of globin genes can be modulated by exogenous factors. The findings raise the possibility that the phenotype of HPFH is not simply the direct result of mutations in or around globin genes but the consequence of the mutations on the interaction of globin genes with trans-acting regulatory factors.

Characterization of the erythropoietic precursors (BFU-E) in a patient with juvenile chronic myelogenous leukaemia by the analysis of G gamma and A gamma globin chains

In order to investigate the pathogenesis of juvenile chronic myelogenous leukaemia (J-CML) we examined the biosynthetic rates of G gamma and A gamma globin chains in the erythropoietic bursts from the bone marrow of a patient with J-CML. Globin chains were labelled with 14C-labelled amino acids, separated by isoelectric focusing and quantitated by fluorography. The synthesis of gamma-chains in the erythropoietic bursts comprised 89.0% of the total non-alpha-chains. The G gamma:A gamma ratio was 0.67, which is within the ratios obtained in newborns. Furthermore, individual erythropoietic bursts contained varying ratios of both gamma and beta chains and all revealed more G gamma than A gamma chain synthesis. The relative proportions of G gamma and total gamma chain biosynthesis in 62 separate erythropoietic bursts were 0.69 +/- 0.06 and 0.86 +/- 0.06, respectively. Cumulative frequency distributions of individual bursts differing in the ratios of gamma/(gamma + beta) and G gamma/(G gamma + A gamma) approached normal frequency distributions. These results suggest that the levels of Hb F in J-CML are controlled by qualitative changes in a single population of erythropoietic precursors, in which normal switching of the G gamma:A gamma ratio has not occurred, rather than by the abnormal proliferation of an F-cell clone.

The synthesis of adult hemoglobins during hepatic erythropoiesis in the calf fetus

We investigated hemoglobin synthesis in suspension cultures of liver erythroid cells obtained from calf fetuses of 103 to 198 days. A significant amount of radioactivity was associated with adult hemoglobins which were separated from the fetal hemoglobins by isoelectric focusing, even after purification of the cell hemolysates by chromatography on Sephadex G-100. A radioactive beta-globin fraction was isolated by chromatography on carboxymethyl-cellulose from hemolysates, which were first fractionated on Sephadex G-100. Fingerprint analysis of peptides obtained by trypsinolysis of radioactive beta-globin chains revealed that its structure was closely related to that of beta-globin, isolated from cow bone marrow cells. The amount of beta-globin which was synthesized by calf liver cells varied from 0.3 to 3.5% of the non-alpha globin chains and remained at a low level for all the fetuses which were studied. Our results indicate that the bovine fetal liver is a valuable model to investigate the switch from fetal to adult hemoglobin synthesis.

Development of a screening system for detection of somatic mutations. I. Enzyme immunoassay for detection of antibodies against specific hemoglobin determinants

A solid-phase enzyme immunoassay for the detection of antibodies, specific for hemoglobin (Hb) is described. The application of glutaraldehyde resulted in a sensitive assay and allowed the use of urea, which is an important advantage if polypeptides not soluble in aqueous buffers are to be used. Mutation-carrying Hb chains can be purified, solubilized in urea and used in the immunoassay to monitor the purification and selection of antibodies specific for these variants. Specific antibodies are the main tools for the development of a hemoglobin-locus mutation system for detection of potentially mutagenic environmental agents. With erythrocytes as target cells, this system permits in vivo monitoring of subjects under exposure. Conventional antibody production, however, frequently turns out to be unsuccessful. The production of monoclonal antibodies has several advantages over conventional antibody production, but a sensitive antibody screening system is essential. Because of the sensitivity and the ease with which a large panel of antibody fractions against a vast panel of Hb antigens can be examined, the described immunoassay has potential value for the screening of hybridoma cultures.

Neonatal screening of beta-thalassemias by thin layer isoelectric focusing

As an alternative to the recently proposed screening for beta-thalassemias by isoelectric focusing (IEF) of denatured globin chains in urea-detergent gels [6], IEF of intact hemoglobins, obtained from umbilical cord blood in neonatal units, is reported here. For maximum separation, IEF should be performed in nonlinear pH gradients, in gels containing 0.2 M beta-alanine and 0.2 M 6-amino caproic acid, which flatten the pH gradient around pH 7, thus increasing the resolution between HbA and HbFac. The method can unambiguously detect homozygous and heterozygous beta-thalassemic conditions. A bimodal distribution of HbA at birth has been found: In heterozygous patients, HbA values of 9.02% (range 6.8-9.98%) have been found while in normal newborns HbA levels of 20.34% (range 11.02-30.6%) have been demonstrated.