Molecular analysis and nematode resistance association of a polymorphism at the 5′ end of the sheep IgE gene

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Previous work using Southern analysis of genomic DNA detected a polymorphism at the 5′ end of the sheep and cattle IgE gene. Identical length differences found between fragments following digestion with restriction enzymes indicated that the basis for the polymorphism was an insertion/deletion event. To characterise the polymorphism, the entire cattle and sheep Cε genes were sequenced including 668 bp of 5′ untranslated DNA. Sequence comparison revealed a high degree of similarity between the ovine and bovine genes at both the nucleotide and amino acid level. A feature of the 5′ untranslated DNA was the presence of an 87 bp repeat starting at −365 upstream of the Cε start site. PCR primers were designed to span most of the 5′ untranslated sequence, including the repeat unit, and used to amplify genomic DNA from a panel of 40 sheep. Three alleles were found with frequencies of 0.7, 0.29, 0.01 which were identical to the Southern analysis results. Sequencing of the two commonest alleles revealed the basis for the polymorphism was a 36 bp deletion from the 87 bp repeat. Association studies in a sheep selection flock phenotypically assessed for parasite resistance found a highly significant association between one of the IgE alleles and resistance to the intestinal nematode parasite Trichostrongylus colubriformis ( P=0.005). Attempts to confirm this finding in two other flocks using linkage analysis and genotype association failed to find any significant associations between the IgE polymorphism and resistance to either T. colubriformis or Haemonchus contortus.