A comprehensive analysis of germline and expressed immunoglobulin repertoire in the horse

Based on the recently released horse genome, we have characterized the genomic organization of the horse Ig gene loci. The horse IgH locus in genomic scaffold Un0011 contains 40 D-H segments, 8J(H) segments and 50 V-H segments. The Ig kappa locus contains only a single C-kappa gene. 5 J(kappa) segments and a 60 V-kappa segments, whereas the Ig lambda locus contains 7 C-lambda genes each preceded by a J(lambda) gene segment. A total of 110 V-lambda segments with the same transcriptional polarity as J(lambda)-C-lambda were identified upstream of the J(lambda)-C-lambda cluster. However, 34 V-lambda segments locating downstream of the J(lambda)-C-lambda cluster showed an opposite transcriptional polarity. Our results reveal that the horse germline V repertoires were more complex than previously estimated. By analyzing the cloned IgH/L cDNA, we further showed that several selected V subgroups were utilized in the expressed V-H, V-kappa, or V-lambda and a high frequency of nucleotide deletions and insertions were introduced by somatic hypermutation in these expressed V genes. (C) Published by Elsevier Ltd.