CAG-GFP Adeno-associated virus(AAV Serotype 1)

Adeno-associated virus (AAV) is a powerful tool for gene delivery into the brain and has been used for transgene expression in the cerebellar cortex. Although the effects of different AAV serotypes on cerebellar Purkinje cells have been investigated, cell-type-specific transgene expression has been difficult to achieve. Here, researchers used AAV serotype 1 with two specific promoters, the Ca2+/calmodulin-dependent protein kinase II alpha (CaMKIIα) and the minimum region of the GABAA receptor α6 subunit (GABRα6) promoters, and compared their expression patterns in the cerebellar cortex with those of ubiquitous promoters commonly used for AAV-mediated expression. AAVs with ubiquitous promoters, the cytomegalovirus early enhancer/chicken β-actin promoter, and small fragments of the synapsin-1 gene promoter caused ubiquitous expression in all cerebellar neurons tested, whereas AAVs with the CaMKIIα promoter injected into 10-day-old mice achieved selective expression in Purkinje cells. In addition, they developed AAVs with the GABRα6 promoter and succeeded for the first time in expressing transgenes specifically in granule cells. Fresh cerebellar slices from mice injected with these AAVs can be used for physiological experiments, such as patch clamp recordings, optogenetic imaging, and stimulation. Therefore, these AAV vectors are useful tools for understanding the basic properties of cerebellar neurons or the mechanisms of cerebellar function.

Here, AAV1-CAG-GFP induced expression in all cells tested in the cerebellar cortex (Figure 1A). In addition, GFP fluorescence was clearly visible in glial cells and their processes, which were stained with an antibody to glial fibrillary acidic protein (GFAP) (Figures 1A and D). The CAG ubiquitous promoter resulted in expression of the transgene in all cell types tested, indicating that the AAV1 used in this study has a broad cellular tropism in the adult mouse cerebellar cortex. The sSyn promoter in combination with AAV has been used to confer exclusive neuronal expression in vitro and in vivo. The researchers tested whether AAV1 with the sSyn promoter (AAV1-sSyn) had any selectivity or preference for gene expression in cerebellar neurons. In adult mice, GFP expression was observed in all neurons of the cerebellar cortex tested, namely Purkinje cells, granule cells, stellate/basket cells, and Golgi cells (Figure 1B). In contrast to AAV1-CAG (Figures 1D), AAV1-sSyn did not result in transgene expression in glial cells (Figures 1B, GFAP). Thus, AAV1-sSyn appears to be useful for transgene expression in most types of cerebellar neurons, as it is combined with transgenic mice that express Cre in specific types of neurons.

Figure 1. Expression of GFP in a broad range of cells of the cerebellum by AAV1-CAG-GFP or AAV1-sSyn-GFP. (Kim Y, et al., 2015)