Different hematological phenotypes caused by extranumerary alpha-Globin genes in sheep native of an endemic TBD region
In Apulia, the selective pressure of endemic hemotropic parasites on farm animals has produced genetic pools tolerant to the diseases caused by these parasites. Investigating the hemoglobin polymorphism of native Apulian sheep, one of us found a relatively high frequency of heterozygotes for [alpha][alpha][alpha] and [alpha][alpha][alpha][alpha] globin haplotypes. Phenotypic variability at the hemoglobin genetic systems induced by hemoparasites is a given fact and the high number of hemoglobinopathies in human populations living in malaria endemic areas is one of the most dramatic example. Given that the presence of extra [alpha]-globin genes causes an additional disadvantage to individuals carrying a [bêta]-thalassemic trait, our working hypothesis was that the additional [alpha]-globin genes in sheep might produce extra [alpha]-globin chains and, consequently, the subject carrying triplicated or quadruplicated haplotypes might exhibit different haematological phenotypes when compared to the normally [alpha][alpha]/[alpha][alpha] homozygotes (NN). Hence, through selection and inbreeding we obtained both [alpha][alpha][alpha] and [alpha][alpha][alpha][alpha] heterozigotes (ED) and [alpha][alpha][alpha] and [alpha][alpha][alpha][alpha] homozygotes (OD). i) Chromatographic RP-HPLC analyses of the globin chains of 66 subjects (18OD, 18ED and 30 NN) were performed. The regression analysis was carried out plotting the number of [alpha]-genes and the [alpha]/[bêta] data obtained by integrating the chromatographic peaks of the different globins; a significant correlation (r=0.95) between the number of [alpha]-genes and the quantity of [alpha]-globin detected was observed with the [alpha]/[bêta] ratio ranging on average from 1.000 in NN individuals to 1.2 and 1.5 in ED and OD subjects respectively. ii) Hematological investigations were carried out using standardized equipment for veterinary haematology. Three different measurements were made for red blood cell count (RBC, hemoglobin content (Hb), packed cell volume (PCV). Mean corpuscular volume(MCV), mean corpuscular hemoglobin (MCH) and mean corpuscolar hemoglobin concentration (MCHC) were calculated and the erythrocyte fragility test was performed. The results revealed blood values that fell within the range of normality but were rather peculiar as a whole. Comparing the erythrocytes of individuals carrying normal arrangements to those of subjects with extra [alpha] genes, the latter appeared to be characterised by few erythrocyte that were bigger in size and had a higher Hb content and a greater osmotic fragility; this hematological picture being consistent with the existence of an unbalanced [alpha]/[bêta] ratio. All these phenomena seem to mimic a thalassemia-like syndrome in sheep and suggest that the relatively high frequency of [alpha][alpha][alpha] and [alpha][alpha][alpha][alpha] haplotypes in native Apulian sheep might be the result of a selective advantage of the corresponding phenotypes in endemic TBD areas. (Texte intégral)
| Main Authors: | , , , |
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| Format: | conference_item biblioteca |
| Language: | eng |
| Published: |
CIRAD
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| Subjects: | L10 - Génétique et amélioration des animaux, phénotype, gène, mouton, http://aims.fao.org/aos/agrovoc/c_5776, http://aims.fao.org/aos/agrovoc/c_3214, http://aims.fao.org/aos/agrovoc/c_8369, |
| Online Access: | http://agritrop.cirad.fr/512060/ |
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| Summary: | In Apulia, the selective pressure of endemic hemotropic parasites on farm animals has produced genetic pools tolerant to the diseases caused by these parasites. Investigating the hemoglobin polymorphism of native Apulian sheep, one of us found a relatively high frequency of heterozygotes for [alpha][alpha][alpha] and [alpha][alpha][alpha][alpha] globin haplotypes. Phenotypic variability at the hemoglobin genetic systems induced by hemoparasites is a given fact and the high number of hemoglobinopathies in human populations living in malaria endemic areas is one of the most dramatic example. Given that the presence of extra [alpha]-globin genes causes an additional disadvantage to individuals carrying a [bêta]-thalassemic trait, our working hypothesis was that the additional [alpha]-globin genes in sheep might produce extra [alpha]-globin chains and, consequently, the subject carrying triplicated or quadruplicated haplotypes might exhibit different haematological phenotypes when compared to the normally [alpha][alpha]/[alpha][alpha] homozygotes (NN). Hence, through selection and inbreeding we obtained both [alpha][alpha][alpha] and [alpha][alpha][alpha][alpha] heterozigotes (ED) and [alpha][alpha][alpha] and [alpha][alpha][alpha][alpha] homozygotes (OD). i) Chromatographic RP-HPLC analyses of the globin chains of 66 subjects (18OD, 18ED and 30 NN) were performed. The regression analysis was carried out plotting the number of [alpha]-genes and the [alpha]/[bêta] data obtained by integrating the chromatographic peaks of the different globins; a significant correlation (r=0.95) between the number of [alpha]-genes and the quantity of [alpha]-globin detected was observed with the [alpha]/[bêta] ratio ranging on average from 1.000 in NN individuals to 1.2 and 1.5 in ED and OD subjects respectively. ii) Hematological investigations were carried out using standardized equipment for veterinary haematology. Three different measurements were made for red blood cell count (RBC, hemoglobin content (Hb), packed cell volume (PCV). Mean corpuscular volume(MCV), mean corpuscular hemoglobin (MCH) and mean corpuscolar hemoglobin concentration (MCHC) were calculated and the erythrocyte fragility test was performed. The results revealed blood values that fell within the range of normality but were rather peculiar as a whole. Comparing the erythrocytes of individuals carrying normal arrangements to those of subjects with extra [alpha] genes, the latter appeared to be characterised by few erythrocyte that were bigger in size and had a higher Hb content and a greater osmotic fragility; this hematological picture being consistent with the existence of an unbalanced [alpha]/[bêta] ratio. All these phenomena seem to mimic a thalassemia-like syndrome in sheep and suggest that the relatively high frequency of [alpha][alpha][alpha] and [alpha][alpha][alpha][alpha] haplotypes in native Apulian sheep might be the result of a selective advantage of the corresponding phenotypes in endemic TBD areas. (Texte intégral) |
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