Differential Evolution of Antiretroviral Restriction Factors in Pteropid Bats as Revealed by APOBEC3 Gene Complexity

Hayward, Joshua A; Tachedjian, Mary; Cui, Jie; Cheng, Adam Z; Johnson, Adam; Baker, Michelle L; Harris, Reuben S; Wang, Lin-Fa; Tachedjian, Gilda

The large number of A3Z1 genes present in the pteropid A3 locus is surprising given the scarcity of this subtype among other mammals (LaRue et al. 2009 ). The presence of 12 A3Z1 genes in pteropid bats indicates an evolutionary advantage for pteropid bats in the maintenance and expansion of this subtype. The most comparable APOBEC3 protein in humans is A3A, the sole APOBEC3 single-domain Z1 protein. A3B and A3G are double-domain proteins that have a Z1 paired with a Z2A domain (fig. 1C ). Endogenous A3A is cytoplasmically FIG. 4 . Antiviral activity of A3 proteins. Vif-deficient HIV-1 was generated in the presence of A3 proteins. Human 293 T cells were transfected with 400 ng of the HIVDvif expression plasmid pIIIBDvif and variable amounts (25-600 ng) of human or bat A3 expression plasmids. TZM-bl indicator cells were inoculated with 293 T cell culture supernatants normalized for viral particles by virion-associated RT activity. Infectivity relative to HIVDvif alone was measured by quantifying luciferase activity in TZM-bl lysates. HIV, human immunodeficiency virus type 1; hA3G, human APOBEC3G; Z1c Iso A, Pteropus alecto APOBEC3Z1c isomer A; Z1c Iso B, Pteropus alecto APOBEC3Z1c isomer B; Z2A Iso A, Pteropus alecto APOBEC3Z2A isomer A; Z2Ba Iso C, P. alecto APOBEC3Z2Ba isomer C; Z3 Iso A, P. alecto APOBEC3Z3 isomer A; Z2Bd-Z3, P. alecto APOBEC3Z2Bd-Z3. Error bars represent the standard error of the mean from three independent assays. Differential Evolution of Antiretroviral Restriction Factors in Pteropid Bats . doi:10.1093/molbev/msy048 MBE located (Land et al. 2013 ) but accesses the nucleus during telophase, the final stage of mitosis ). It has restrictive activity against retrotransposons (Chen et al. 2006; Koito and Ikeda 2013) and viruses including HIV-1, adenoassociated virus, and human papillomavirus (Chen et al. 2006; Berger et al. 2011; Warren et al. 2015) . In humans, evidence suggests that A3Z1 domain-containing proteins may represent a double-edged sword, as potent inhibitors of genomic retrotransposons and a possible threat to the cell's own genomic sequence integrity (LaRue et al. 2008; Roberts et al. 2013; Taylor et al. 2013; Burns et al. 2015; Green et al. 2016 ). One possible reason for the observed expansion of A3Z1 genes in bats may be related to the evolution of flight, which is hypothesized to be an important link to the physiological conditions allowing bats to be sources of high viral diversity (O'Shea et al. 2014 ). Increased metabolic capacity has been linked to the evolution of sustained flight in bats (Shen et al. 2010) , and the by-products of oxidative metabolism include reactive oxygen species that are known to damage cellular DNA (Cooke et al. 2003) . The most notable genetic adaptations involved in the development of flight in bats have been found to exist in the genes responsible for the detection and repair of cellular DNA damage (Zhang et al. 2013; Zhou et al. 2016) . It is possible that enhanced tolerance to DNA damage would allow for the expansion of genes such as A3 whose products are known to cause such damage.