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

Previous work using Southern analysis of genomic DNA detected a polymorphis m at the 5' end of the sheep and cattle IgE gene. Identical length differen ces found between fragments following digestion with restriction enzymes in dicated that the basis for the polymorphism was an insertion/deletion event . To characterise the polymorphism, the entire cattle and sheep CE genes we re sequenced including 668 bp of 5' untranslated DNA. Sequence comparison r evealed a high degree of similarity between the ovine and bovine genes at b oth the nucleotide and amino acid level. A feature of the 5' untranslated D NA was the presence of an :37 bp repeat starting at --365 upstream of the C E 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 t he IgE alleles and resistance to the intestinal nematode parasite Trichostr ongylus 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 t o either 7: colubriformis or Haemonchus contortus. (C) 2001 Elsevier Scienc e B.V. All rights reserved.