期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：48
页码：13815-13820
DOI：10.1073/pnas.1616948113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceCopy number variation is an important source of genetic variation in animal genomes and an evolutionary intermediate in gene family expansion. In this study, we report the presence of a tandem duplication of {beta}-defensin 7 (BD7) among multiple breeds of chickens and a resulting chimeric promoter that appears to result from gene conversion followed by nonallelic homologous recombination. These findings contribute to the understanding of gene family expansion in animals and the role of large gene families in host-defense mechanisms. Defensins constitute an evolutionary conserved family of cationic antimicrobial peptides that play a key role in host innate immune responses to infection. Defensin genes generally reside in complex genomic regions that are prone to structural variation, and defensin genes exhibit extensive copy number variation in humans and in other species. Copy number variation of defensin genes was examined in inbred lines of Leghorn and Fayoumi chickens, and a duplication of defensin7 was discovered in the Fayoumi breed. Analysis of junction sequences confirmed the occurrence of a simple tandem duplication of defensin7 with sequence identity at the junction, suggesting nonallelic homologous recombination between defensin7 and defensin6. The duplication event generated two chimeric promoters that are best explained by gene conversion followed by homologous recombination. Expression of defensin7 was not elevated in animals with two genes despite both genes being transcribed in the tissues examined. Computational prediction of promoter regions revealed the presence of several putative transcription factor binding sites generated by the duplication event. These data provide insight into the evolution and possible function of large gene families and specifically, the defensins.
