Elucidation of the Complicated Scenario of Primate APOBEC3 Gene Evolution.

APOBEC3 proteins play pivotal roles in defenses against retroviruses, including HIV-1, as well as retrotransposons. Presumably due to the evolutionary arms race between the hosts and retroelements, APOBEC3 genes have rapidly evolved in primate lineages through sequence diversification, gene amplification and loss, and gene fusion. Consequently, modern primates possess a unique set or "repertoire" of APOBEC3 genes. The APOBEC3 gene repertoire of humans has been well investigated. There are three types of catalytic domains (Z domain; A3Z1, A3Z2, and A3Z3), 11 Z domains, and 7 independent genes, including 4 genes encoding double Z domains. However, the APOBEC3 gene repertoires of nonhuman primates remain largely unclear. Here, we characterize APOBEC3 gene repertoires among primates and investigated the evolutionary scenario of primate APOBEC3 genes using phylogenetic and comparative genomics approaches. In the 21 primate species investigated, we identified 145 APOBEC3 genes, including 69 double-domain type APOBEC3 genes. We further estimated the ages of the respective APOBEC3 genes and revealed that APOBEC3B, APOBEC3D, and APOBEC3F are the youngest in humans and were generated in the common ancestor of Catarrhini. Notably, invasion of the LINE1 retrotransposon peaked during the same period as the generation of these youngest APOBEC3 genes, implying that LINE1 invasion was one of the driving forces of the generation of these genes. Moreover, we found evidence suggesting that sequence diversification by gene conversions among APOBEC3 paralogs occurred in multiple primate lineages. Together, our analyses reveal the hidden diversity and the complicated evolutionary scenario of APOBEC3 genes in primates. In terms of virus-host interactions and coevolution, the APOBEC3 gene family is one of the most important subjects in the field of retrovirology. APOBEC3 genes are composed of a repertoire of subclasses based on sequence similarity, and a paper by LaRue et al. provides the standard guideline for the nomenclature and genomic architecture of APOBEC3 genes. However, it has been more than 10 years since this publication, and new information, including RefSeq, which we used in this study, is accumulating. Based on accumulating knowledge, APOBEC3 genes, particularly those of primates, should be refined and reannotated. This study updates knowledge of primate APOBEC3 genes and their genomic architectures. We further inferred the evolutionary scenario of primate APOBEC3 genes and the potential driving forces of APOBEC3 gene evolution. This study will be a landmark for the elucidation of the multiple aspects of APOBEC3 family genes in the future.