Cloning and expression of activation induced cytidine deaminase from Bos taurus

Activation induced cytidine deaminase is an enzyme crucial to somatic hypermutation and gene conversion, processes that are essential for the diversification of Ig V genes. The bovine Ig repertoire appears to be diversified by mechanisms that are significantly different to those that operate in humans and mice. This study set out to test the hypothesis that differences in the organization, coding sequence, expression or genomic location of the bovine AICDA gene enables the encoded enzyme to catalyse the unusual Ig diversification mechanism seen in cattle as well as conventional antigen-driven mutation. Characterization of bovine AICDA excluded the first two possibilities. AICDA expression was detected in lymphoid tissues from neonatal and older cattle, but AICDA cDNA could not be detected in muscle tissue. The pattern of gene expression did not therefore differ from that in other vertebrates. The AICDA cDNA was cloned and expressed successfully in Escherichia coli generating a phenotype consistent with the mutating action of this deaminase. Using a whole genome radiation hybrid panel, bovine AICDA was mapped to a region of bovine chromosome 5 syntenic with the location of human AICDA on chromosome 12. We conclude that the unusual nature of Ig diversification in cattle is unlikely to be attributable to the structure, sequence, activity or genomic location of bovine AICDA.