Expression of triplicated and quadruplicated alpha globin genes in sheep

Quintuple α-Globin Gene: A Novel Allele in a Sudanese Man

Multiple alpha-globin repeats have previously been discovered in humans and other mammals. A quintuple alpha-globin gene (alphaalpha/alphaalphaalphaalphaalpha) was found in a Sudanese male undergoing evaluation for microcytosis.

Three new alpha-globin variants: Hb Itapira [alpha30(B11)Glu-->Val (alpha1)], Hb Bom Jesus Da Lapa [alpha30(B11)Glu-->Ala (alpha1)] and Hb Boa Esperança [alpha16(A14)Lys-->Thr (alpha2)]

Three novel alpha-globin variants were found during a screening program for hemoglobinopathies in blood donors at the UNICAMP Hematology and Hemotherapy Center, Campinas, State of São Paulo, Southeastern Brazil. They were named for the town of origin of the carrier as Hb Itapira [alpha30(B11)Glu-->Val], Hb Bom Jesus da Lapa [alpha30(B11)Glu-->Ala] and Hb Boa Esperança [alpha16(A14)Lys-->Thr]. Hb Itapira, like Hb Bom Jesus da Lapa, shows an electrophoretic mobility similar to that of Hb S [beta6(A3)GluVal, GAG-->GTG] at alkaline pH; it is associated with a triplicate alpha-globin allele (alphaalphaalpha(anti 3.7)) and corresponds to only 5.5% of the total hemoglobin (Hb). Hb Boa Esperança, found in two different individuals, moves faster than Hb A and exhibits an abnormal functional performance.

Functional effect of haemoglobin polymorphism on the haematological pattern of Gentile di Puglia sheep

The relationship between haemoglobin polymorphism and haematological pattern were studied in Gentile di Puglia, the Apulia Merino native breed. In a sample of 292 individuals, on five different farms, alpha- and beta-globin genetic polymorphism was investigated. A remarkable polymorphism was detected especially at alpha-globin gene where the variations concerned both the quality of the gene product and gene expression. Triplicated and quadruplicated alpha-globin genes were observed in 8.6% and 1.2% of the alpha-haplotypes respectively. At beta-globin (HBB) locus, predominance of HBB(B) allele was found in all flocks, while HBB(A) overall frequency was around 11.2%. Moreover, the effect of genotypes at globin systems on haematological data was evaluated on 289 animals. A significant effect was detected for HBB locus on haematocrit (HCT) and mean corpuscular volume (MCV), with decreasing HCT and MCV for decreasing number of HBB(A) alleles in the genotype. The opposite trend was observed for mean corpuscular haemoglobin concentration. The advances presented by this paper give reasons for inferring that BB genotypes can be expected to be more resilient to climatic stress and to local parasites.

A novel molecular basis for β thalassemia intermedia poses new questions about its pathophysiology

During a study of the molecular basis for severe forms of β thalassemia in Sri Lanka, 2 patients were found to be heterozygous for β thalassemia mutations. Further analysis revealed that one of them has a previously unreported molecular basis for severe thalassemia intermedia, homozygosity for quadruplicated α globin genes in combination with heterozygous β thalassemia. The other is homozygous for a triplicated α globin gene arrangement and heterozygous for β thalassemia. Their differences in clinical phenotype are explainable by the interaction of other genetic factors and, in particular, their early management. The clinical course of the 2 propositi underlines the importance of full genotyping and a long period of observation before treatment is instituted, particularly in patients with β thalassemia intermedia associated with extended α globin gene arrangements. The hemoglobin (Hb) F levels in these patients with severe β thalassemia intermedia, compared with other forms of this condition in the Sri Lankan population and elsewhere, are unusually low, a consistent finding in extended α globin gene interactions and in dominant β thalassemia, raising the possibility that increased levels of HbF production in β thalassemia may require mutations at both β globin gene loci.

The alpha chains of goat hemoglobins: old and new variants in native Apulian breeds

Blood samples were collected from 324 goats belonging to the native Apulian breeds Garganica and Jonica; 60 Alpine goats were also sampled to serve as a comparison. Hemoglobin phenotypes were analyzed with isoelectric focusing in a pH range of 6.7-7.7. Heterogeneity of globin chains was evidenced both by AUT-PAGE and RP-HPLC. The primary structure of four alpha globins was analyzed by combined mass spectrometry approaches. Two of these globins had never been sequenced before. One was a new alpha variant, an allele of the HBA1A gene from which it differed for the mutation A26T and has been registered with a low frequency only in Apulian breeds; the other was a globin encoded by the HBA2 locus, whose primary structure was previously derived from the corresponding gene. The two alleles recorded at the HBA2 locus presented a different frequency in the three breeds but may be considered to be generally rather common. Notwithstanding the sample size no goat was found to exhibit HbA1B. The authors discuss their findings in the light of the results reported by other researchers and argue that, in spite of what had been inferred in pioneer works on goat hemoglobins, HBA1B is not a common allele.

The phenotype of sheep hemoglobins containing distinct alpha chains is influenced by beta chain genotype

In sheep carrying simultaneously extra alpha-globin genes (triplications and quadruplications) and two alpha-chain allelic variants, a gradient of decreasing expression of the downstream genes was previously reported. We show here that in these sheep the proportions of the normal and variant Hbs reflect not only the position effect, but also the differential affinity of one of the alpha variants for the betaA and betaB allelic chains.

Sheep alpha-globin gene sequences: implications for their concerted evolution and for the down-regulation of the 3' genes

In sheep as in man and most other mammals, there are two alpha-globin genes (I alpha and II alpha), which are expressed at different levels, the upstream gene being the most efficient. In alpha-globin gene triplication and quadruplication, this trend is confirmed, i.e., the alpha-chain output of the downstream genes progressively decreases. In this study, we have determined the complete sequence of the cDNAs and of both the introns in a triple-alpha haplotype in which each gene could be recognized for the presence of distinct alleles. The sequence analysis reveals that the bodies of the three alpha-globin genes are essentially identical (99.9% homology) and moreover indicates that the down-regulation of additional alpha-globin genes in sheep is not the effect of sequence variation from the Cap to the Poly(A) addition sites. This striking similarity among alpha-genes is higher than that seen in other mammals and is probably sustained by particularly efficient mechanisms of gene conversion and cross-over fixation.

Detection by reversed-phase HPLC of trace amounts of the alpha 113His globin chain in a sheep homozygous for a quadruple alpha-globin gene chromosome

1. In sheep alpha alpha 113His and alpha D alpha alpha 113His globin gene haplotypes, the percentage gene efficiencies, from the 5' to the 3' end, are about 32-18 and 30-14-6, respectively. 2. We previously found that in a alpha alpha alpha alpha homozygote there may be a 1-2% alpha 113His chains, which however were difficult to resolve from alpha 113Leu chains by CMC chromatography. 3. We report here the experimental conditions which allowed a neat resolution of the 1% alpha 113His chain peak by RP-HPLC. 4. This finding strongly suggests the occurrence of the alpha D alpha alpha alpha 113His haplotype where the percentage gene efficiencies are 30-(14-5)-1, supporting the existence of a gradient of decreasing expression in multiple alpha-globin gene haplotypes.