Hemoglobins in sheep: multiple differences in amino acid sequences of three beta-chains and possible origins

Genomic Tools for the Identification of Loci Associated with Facial Eczema in New Zealand Sheep

Facial eczema (FE) is a significant metabolic disease that affects New Zealand ruminants. Ingestion of the mycotoxin sporidesmin leads to liver and bile duct damage, which can result in photosensitisation, reduced productivity and death. Strategies used to manage the incidence and severity of the disease include breeding. In sheep, there is considerable genetic variation in the response to FE. A commercial testing program is available for ram breeders who aim to increase tolerance, determined by the concentration of the serum enzyme, gamma-glutamyltransferase 21 days after a measured sporidesmin challenge (GGT21). Genome-wide association studies were carried out to determine regions of the genome associated with GGT21. Two regions on chromosomes 15 and 24 are reported, which explain 5% and 1% of the phenotypic variance in the response to FE, respectively. The region on chromosome 15 contains the β-globin locus. Of the significant SNPs in the region, one is a missense variant within the haemoglobin subunit β (HBB) gene. Mass spectrometry of haemoglobin from animals with differing genotypes at this locus indicated that genotypes are associated with different forms of adult β-globin. Haemoglobin haplotypes have previously been associated with variation in several health-related traits in sheep and warrant further investigation regarding their role in tolerance to FE in sheep. We show a strategic approach to the identification of regions of importance for commercial breeding programs with a combination of discovery, statistical and biological validation. This study highlights the power of using increased density genotyping for the identification of influential genomic regions, combined with subsequent inclusion on lower density genotyping platforms.

Studies of haemoglobin types in barbary sheep (Ammotragus lervia)

1. Two haemoglobin types, haemoglobins Amm-C and Amm-B, were observed in five Barbary sheep (Ammotragus lervia). One animal was homozygous for haemoglobin Amm-C, a second was homozygous for haemoglobin Amm-B, and three were heterozygous for both. 2. Amino acid analyses of the globin from haemoglobin Amm-B showed that this type was related to, but not identical with, haemoglobin B of the domestic sheep. 3. The beta-chain of haemoglobin Amm-C was found to be composed of 141 amino acid residues. Its amino acid composition differed from that of the beta(C)-chain of the anaemic domestic sheep in at least 14 residues. The Amm-beta(C)-chain contained one isoleucyl residue. 4. The amino acid compositions of tryptic peptides T-1, T-2, T-13 and T-14 of the Amm-beta(C)-chain were similar to those of the sheep beta(C)-chain. Peptides T-3, T-4, T-6, T-7, T-8, T-11 and T-15 were the same as the corresponding peptides of the sheep beta(A)- and beta(C)-chains. Peptide T-5 and to a smaller extent peptide T-9 resembled the corresponding peptides of the sheep beta(A)-chain, and peptide T-10 was identical with peptide gammaT-10 of sheep haemoglobin F. Peptide T-12 was not recovered. 5. The results of these investigations were interpreted as being indicative that the structural Amm-beta(C)-gene is closely related to the beta(C)-gene of sheep, from which through domestication the present domestic sheep originated.

Tertiary conformational transition in sheep hemoglobins induced by reaction with 5,5 -dithiobis(2-nitrobenzoate) and by binding of inositol hexakisphosphate

We have determined the second-order reverse rate constant, k(R), for the reaction of 5,5 -dithiobis(2-nitrobenzoate) - DTNB - with sheep hemoglobins as a function of pH from values of the second-order forward rate constant, k(F), and the equilibrium constant, K(equ), at 25 degrees C: k(R)=k(F)K(equ). We demonstrate that (i) inositol hexakisphosphate (inositol-P(6)) decreases k(F) and k(R) by increasing K(rt), the rright harpoon over left harpoont tertiary conformation transition constant; (ii) the conformation favored for both the forward and reverse reactions is the r conformation. For stripped hemoglobin we obtain from the k(F) data a t isomer population of 34.6% (+/-14) prior to reaction with DTNB; from the k(R) data we calculate a t isomer population of 44.8% (+/-4) following reaction with DTNB. In the presence of inositol-P(6) the latter value is increased to 79.5% (+/-2). These results demonstrate that an allosteric transition occurs on reaction with DTNB and on inositol-P(6) binding.

Differences in the DNA restriction patterns between sheep with HbA and HbB

DNA samples obtained from sheep homozygous for HbA, for HbB and heterozygous were subjected to Southern blot analysis using a goat beta F and a rabbit beta 1-globin gene as probes. Sheep homozygous for HbA show a different restriction pattern from that of sheep homozygous for HbB with each of the used endonucleases. The DNAs from moufflon and sheep homozygous for HbA show indistinguishable restriction patterns with some endonucleases. By means of double digestions it has been possible to construct restriction maps of the beta B and beta C genes and to confirm the absence of the beta C gene in HbB sheep.

Transition of haemoglobin between two tertiary conformations: Inositol hexakisphosphate increases the transition constant and the affinity of sheep haemoglobin for 5,5'-dithiobis(2-nitrobenzoate)

The equilibrium constant (K(equ)) for the reaction of 5,5'-dithiobis(2-nitrobenzoate) - DTNB - with the CysF9[93]beta sulphydryl group of the haemoglobins of the sheep decreases by about two orders of magnitude between pH approximately 5.6 and 9.2: from a mean of 7.2+/-1 to a mean of 0.044+/-0.01. Calculations from the pH dependence of K(equ) show that in the r-t tertiary conformational transition of haemoglobin the t isomer population is 50.7 and 61.8% for the major and minor haemoglobins, respectively. In the presence of inositol hexakisphosphate (inositol-P(6)), K(equ) increases for both haemoglobins by about an order of magnitude through most of the pH range. The t isomer population also increases to 82.1 and 79.6% for the major and minor haemoglobins, respectively. These results indicate that inositol-P(6) increases the affinity of the sulphydryl for DTNB by increasing the population of the t isomer. It is highly probable that a minimum four-state model that includes the r-t transition is required for a full understanding of haemoglobin function.

Electrospray ionization mass spectrometric analysis of blood for differentiation of species

The National Fish and Wildlife Forensic Laboratory is responsible for the determination of species of birds, reptiles, and mammals from the United States, as well as international species falling under the protection of CITES treaties. We have recently found electrospray ionization mass spectrometry to be an effective means of rapidly analyzing blood samples for species identification. Nearly 1000 individuals were analyzed which comprised 62 species represented by birds, mammals, and reptiles. Whole blood and dried blood samples were analyzed without purification to provide simultaneous molecular weights from the alpha- and beta-proteins present in each sample's hemoglobin. The combination of the two molecular weights for the hemoglobin proteins (i.e., alpha/beta-pairs) was used as species determining markers. In all, 133 distinctive alpha/beta-pairs were observed from the individuals analyzed. Despite the variability in the hemoglobins evaluated, 86% of these alpha/beta-pairs were found to be diagnostic for a particular species to the exclusion of all other species studied. No other single protein system studied by a single analytical technique can so effectively resolve species from a wide range of taxa as can the hemoglobin system when analyzed by electrospray ionization mass spectrometry.

A comparison of the beta A-and beta B-globin gene clusters of sheep

Domestic sheep have two common alleles at the adult beta-globin locus, beta A and beta B. Here we report the structure of the beta-globin locus of A-haplotype sheep. The locus consists of 12 genes, organized as a triplicated 4-gene set: 5' epsilon 1-epsilon II-psi beta I-beta C-epsilon III-epsilon IV-psi beta II-beta A-epsilon V-epsilon VI-psi beta III-beta F 3'. This arrangement is identical to that of the closely related goat locus. Sheep with the B haplotype have a locus arrangement consisting of a duplicated four-gene set, lacking the beta C gene as well as three other genes present in A sheep and goats. In order to understand the evolutionary history of the B sheep locus, we have sequenced the beta B gene from these sheep, and the beta C gene from A-haplotype sheep, and compared the sequences to those of the sheep beta A, goat beta C, and beta A, and cow adult beta genes. Our results indicate that the beta B gene has diverged recently from the beta A gene, and therefore the beta B locus structure may have resulted from a recent deletion from a triplicated locus.

Differences in the number of embryonic and pseudo-beta-globin genes between HbA and HbB sheep

DNA samples obtained from 8 goats, 1 moufflon, and 84 sheep with HbA, HbAB, and HbB belonging to different breeds were digested with BamHI, EcoRI, HindIII and PstI and probed with the 5' end of the goat epsilon IV- and psi beta Z-globin genes. Sheep homozygous for HbA show a different restriction pattern than sheep homozygous fo HbB with each of these endonucleases. The main difference is that HbB sheep lack the epsilon II and psi beta X genes. These results, in addition to those previously obtained using a probe specific for beta-globin genes, suggest that HbB sheep probably lack the preadult four-gene set. The DNAs from moufflon and sheep homozygous for HbA show indistinguishable restriction patterns. Furthermore, a number of restriction fragment length polymorphisms (RFLPs) are detected in the epsilon IV and psi beta Z DNA regions, and one HindIII RFLP in the epsilon VI DNA region.

The reaction kinetics of four sheep haemoglobins with identical alpha-chains

Sheep haemoglobins A, B, C and F are known to have identical alpha-chains but differing beta-chains. Rate constants were determined for the combination of CO with these four deoxy haemoglobins (l') and for the dissociation of O2 from the fully saturated tetramers (k4) from 15 to 38 degrees C at physiological pH in the presence of CO2, and at pH 9.1 in the absence of CO2. The constant for the replacement of O2 from the tetramer by CO (m' infinity) and the ratio of the combination constants of CO and O2 with the three parts saturated tetramer (l'4/k'4), were also determined over this range of temperature at physiological pH in the presence of CO2. In no respect did Hb A differ from Hb C. Apart from this the values for l' differed significantly between each pair of haemoglobins. The constant k4 showed significant differences only when Hb B was compared with Hb A or Hb C. Values of m' infinity were similar for the four haemoglobins; and the values of the ratio l'4/k'4 were similar for Hbs A, C and F, and about half as great for Hb B. The results do not support the hypothesis of predominance of the alpha-chains in determining the rate of ligand combination with the desaturated tetramer. It is suggested that faster rate of release of O2 from Hb B may be due to its having lysine at position HCl in the beta-chain whereas the other haemoglobins have arginine.

Possible duplication of the hemoglobin alpha chain locus in sheep

Only one type of alpha chain has been described so far in the hemoglobins of adult domestic sheep. A variant (Hb D) of the alpha chain, characterized by a substitution glycine leads to aspartic acid at position 15, has been described in Yugoslavian sheep. In this paper we report the identification of a second alpha chain (alpha 2), observed in several sheep when the globin was analyzed by CM-cellulose chromatography or the total hemolysate submitted to isoelectric focusing. The ratio of this chain to the usual one (alpha 1) in the globin of different animals is equal to either 1 : 2 or 1 : 4. The structural difference between alpha 1 and alpha 2 chains consists in the replacement of a leucine residue by an histidine in the position 113 or 114 of the polypeptide chain. Preliminary data on the frequency of the alpha 2 chain in eight domestic breeds indicate that this chain is fairly common, being present in 15 out of 40 animals examined. The results of breeding experiments between sheep of an appropriate alpha chain phenotype suggest the possibility of a duplication of the hemoglobin alpha locus in the Ovinae.

Higher oxygen affinity of sheep Hb C compared to Hb A and Hb B

Sheep which have Hb A, synthesize the perinatal Hb C in response to severe tissue hypoxia. It is known that Hb A displays a higher oxygen affinity than Hb B. The results of this study indicate that Hb C exhibits an oxygen affinity and a Bohr effect higher than those of Hb A and Hb B.

Hemoglobin switching in sheep and goats. V. Effect of erythropoietin concentration on in vitro erythroid colony growth and globin synthesis

Erythroid colonies were generated in response to erythropoietin in plasma clot cultures of sheep and goat bone marrow cells. At low concentration erythropoietin only hemoglobin A (betaA globin) was synthesized in goat cultures, but at high concentrations 50% of the hemoglobin synthesized was hemoglobin C (betaC globin). This effect of erythropoietin on the expression of a specific beta globin gene was manifested only after 72 h in vitro and followed the development of erythroid colonies. Sheep colonies behaved differently from those of goat in that little or no betaC globin synthesis occurred even at high erythropoietin concentration. To investigate this difference, sheep marrow cells were fractionated by unit gravity sedimentation. The erythroid colony-forming cells sedimented more rapidly (3.5-6mm/h) than the hemoglobinized eththroid precursors (1-3.5 mm/h), suggesting that the colonies were formed from an early erythroid precursor, However, the colonies formed from the sheep marrow fractions synthesized only betaA globin even at concentrations of erythropoietin sufficient to stimulate betaC globin synthesis in goat colonies. Morphologically, the goat colonies were larger and more mature than those of the sheep. By 96 h in vitro three-fourths of the goat colonies contained enucleated red cells compared to only 3% of the sheep colonies. Thus, erythropoietin had an equivalent effect in stimulating erythroid colony growth from the marrow of both species although there were both biochemical and morphological differences between the colonies. Hemoglobin switching appeared to require exposure of an early precursor to high erythropoietin concentration, but the results with sheep marrow suggested that the rate of colony growth and cellular maturation might also be important.

Activation of hemoglobin C synthesis in sheep marrow culture

Erythropoietin preferentially stimulates hemoglobin C synthesis in suspension cultures of marrow cells from sheep homozygous for hemoglobin A; the amount of synthesis is dependent on the dose of erythropoietin and is blocked by antiserum to erythropoietin. The results provide the first in vitro evidence that erythropoietin mediates the hemoglobin A --> C "switch" in sheep and indicate that bone marrow cultures may be used to investigate the mechanisms involved in the preferential gene activation characteristic of the hemoglobin A --> C system.

Hemoglobin switching in sheep and goats: change in functional globin messenger RNA in reticulocytes and bone marrow cells

ANEMIA CAUSES A CHANGE IN THE TYPE OF CIRCULATING HEMOGLOBIN IN GOATS AND CERTAIN SHEEP: HbA (alpha(2)beta(2) (A)) is replaced by HbC (alpha(2)beta(2) (C)). We have isolated globin mRNA from erythroid cells of anemic and nonanemic animals to investigate the mechanism whereby anemia causes this switch. To study several stages in transition from beta(A) to beta(C) synthesis, active globin mRNA was isolated from bone marrow cells, as well as from reticulocytes. By assaying these globin mRNAs in a rabbit reticulocyte cell-free system, we have demonstrated that the switch from beta(A) to beta(C) globin synthesis is mediated via a change in functional globin mRNA.

Gene selection in hemoglobin and in antibody-synthesizing cells

Close linkage of mutually exclusive genes occurs in the non-alpha chain hemoglobin genes and in the immunoglobulin genes of man and other mammals. The expression of one gene in the cluster precludes the expression of any other linked gene. A simple, testable theory of gene selection called "looping-out excision"which was designed only to explain this mutual exclusivity in the hemoglobin system is described. The theory is closely concordant with a wide range of previously unexplained findings concerning hematopoiesis- including the developmental changes of hemoglobins, the increases in immature or fetal forms of hemoglobin that accompany anemia, and with the distribution of adult and fetal hemoglobins among erythrocytes during normal embryogenesis and in various pathological conditions. One corollary of this theory is that erythroid tissue in the normal adult bone marrow is constantly recapitulating the developmental stages of its embryogenesis. Another corollary is that the selection from among the linked globin genes occurs independently on the two chromosomes of the diploid organism. Both of these corollaries are supported by the available data. The same theory of gene selection is also remarkably consistent with known data for immunoglobulin synthesis; it could explain not only the mutually exclusive activation of linked variable genes but also the splicing which occurs between genetically linked variable and constant region genes for the immunoglobulin polypeptide chains. The agreement between these two different tissues is considered to be strong evidence that the proposed mechanism is correct at least in broad outline. Evidence from the genetics of maize and of drosophila also supports this theory of somatic tissue variegation. On the basis of these comparisons, I suggest that looping-out excision probably occurs also in other tissues and may be one means of gene selection and activation in differentiating cells.

Silent hemoglobin alpha genes in apes: potential source of thalassemia

Small quantities of unusual hemoglobins were found in 1 of 37 chimpanzees and 2 of 6 gorillas. In each genus these hemoglobins contain unique alpha chains that differ from the ordinary by eight to nine scattered amino acid changes. The unusual chains arise from a hitherto undetected hemoglobin (3)alpha locus. No (3)alpha products are found in most apes; accordingly, (3)alpha is considered synthetically inactive in all but a few reversion mutants. Indirect evidence that the inactive (3)alpha locus is juxtaposed to an active alpha locus together with the supposition that (3)alpha exists in man provides a setting wherein thalassemia might be produced by nonhomologous recombination between two loci.

Erythropoietic kinetics in sheep studied by means of induced changes in hemoglobin phenotype

This investigation is concerned with the kinetics of the reciprocal relationship between sheep hemoglobin (Hb) A and Hb C formation in response to anemia. The relative synthesis of the hemoglobin types was assessed at various times in bone marrow erythroid cells incubated in vitro with (59)Fe. The changeover from Hb A to Hb C formation lagged by about 3 days behind the development of anemia and was complete within about 11 days. After recovery from anemia the reciprocal change back to preanemic conditions proceeded at a much slower rate, Hb C formation gradually declining to unmeasurable levels over about 25 days. Infusions of plasma with high erythropoietin titre induced the formation of relatively large quantities of Hb C in erythroid cells of nonanemic sheep, demonstrating the central importance of a humoral mechanism in the change of expression of the hemoglobin genes. THE FOLLOWING CONCLUSIONS WERE DRAWN: hemoglobin phenotype is determined at a stem cell level. Erythroid stem cells appear to undergo gradual renewal. The identity of the plasma factor which induces Hb C formation is not yet known; it is not present in plasma from nonanemic sheep, and its production is not dependent upon hemoglobin genotype. If the plasma factor turns out to be erythropoietin, then this hormone must have an important influence on the pool of erythroid stem cells.