APOBEC3G expression is restricted to neurons in the brains of pigtailed macaques.

The Vif protein of human immunodeficiency virus-1 (HIV-1) has been shown to interact with members of the APOBEC family of cytidine deaminases, particularly APOBEC3G/F. In this study, we isolated RNA from 12 regions of the brain from two pigtailed macaques that were exsanguinated and perfused with saline. Our results indicate that APOBEC3G was detected in all regions of the brain analyzed. Immunoblot analysis using lysates prepared from these same regions of the brain and a monoclonal antibody to APOBEC3G confirmed the RT-PCR findings. To determine which cell types express APOBEC3G, immunohistochemical studies were performed using this monoclonal antibody on whole brain sections. Our results clearly show that the pyramidal neurons within the gray matter of cerebral and cerebellar cortices express APOBEC3G. However, APOBEC3G expression in the pyramidal neurons appeared to be nuclear or associated with nuclei. In contrast to our findings in the cerebral cortex, immunohistochemical analysis of the spleen and kidney tissues revealed that APOBEC3G expression in the cells of these tissues was predominantly cytoplasmic. We further investigated the expression of APOBEC3G in astrocytes. Immunohistochemical staining of serial sections was performed using antibodies to glial fibrillary acidic protein (GFAP) and APOBEC3G. As expected, the cortical and cerebellar white matter showed extensive immunostaining of astrocytes with the antibody against GFAP but a lack of reactivity to the antibody to APOBEC3G. Additionally, Immunoblot analysis of lysates prepared from primary human fetal astrocytes revealed a lack of APOBEC3G expression. Taken together, these results indicate that APOBEC3G expression is restricted to neurons in the brain and that astrocytes and microglia probably do not express this protein or express it at levels undetectable by immunohistochemistry. These finding have implications for the brain as a potential reservoir for Vif-defective viruses.