Evaluation of the Expression Pattern of rAAV2/1, 2/5, 2/7, 2/8, and 2/9 Serotypes With Different Promoters in the Mouse Visual Cortex

This study compared the expression pattern, laminar distribution, and cell specificity of several rAAV serotypes (2/1, 2/5, 2/7, 2/8, and 2/9) injected in the primary visual cortex (V1) of adult C57Bl/6J mice. In order to obtain specific expression in certain neuron subtypes, different promoter sequences were evaluated for excitatory cell specificity: a universal cytomegalovirus (CMV) promoter, and two versions of the excitatory neuron-specific Ca2+/calmodulin-dependent kinase subunit alpha (CaMKII alpha) promoter, CaMKII alpha 0.4 and CaMKII alpha 1.3. The spatial distribution as well as the cell type specificity was immunohistochemically verified. Depending on the rAAV serotype used, the transduced volume expressing reporter protein differed substantially (rAAV2/5 >> 2/7 approximate to 2/9 approximate to 2/8 >> 2/1). Excitatory neuron-specific targeting was promoter dependent, with a surprising difference between the 1.3 kb and 0.4 kb CaMKII alpha promoters. While CaMKII alpha 1.3 and CMV carrying vectors were comparable, with 78% of the transduced neurons being excitatory for CMV and 82% for CaMKII alpha 1.3, the shorter CaMKII alpha 0.4 version resulted in 95% excitatory specificity. This study therefore puts forward the CaMKII alpha 0.4 promoter as the best choice to target excitatory neurons with rAAVs. Together, these results can be used as an aid to select the most optimal vector system to deliver transgenes into specific rodent neocortical circuits, allowing further elucidation of their functions. (C) 2015 Wiley Periodicals, Inc.