Selective transgene expression in cerebellar Purkinje cells and granule cells using adeno-associated viruses together with specific promoters

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 efficacies of different AAV serotypes to transduce cerebellar Purkinje cells were examined, it has been difficult to achieve cell-type specific transgene expression. Here we used AAV serotype 1 with two specific promoters, namely, Ca(2+)/calmodulin-dependent protein kinase II α (CaMKIIα) and the minimum region of the GABAA receptor α6 subunit (GABRα6) promoters, and compared their expression patterns in the cerebellar cortex with the expression patterns of ubiquitous promoters that are often used for AAV-mediated expression. Whereas AAV with ubiquitous promoters, the cytomegalovirus early enhancer/chicken β-actin promoter, and a small fragment of the synapsin-1 gene promoter caused ubiquitous expression in all cerebellar neurons tested, AAV with the CaMKIIα promoter injected into 10-day-old mice enabled selective expression in Purkinje cells. Furthermore, we developed AAV with the GABRα6 promoter, and succeeded for the first time to express the transgene exclusively in granule cells. Fresh cerebellar slices of mice injected with these AAVs were applicable for physiological experiments, such as patch clamp recording, optogenetic imaging, and stimulation. Thus, these AAV vectors are useful tools towards understanding the basic properties of cerebellar neurons or mechanisms of cerebellar functions. Particularly, selective expression in Purkinje or granule cells is useful for analyses using genetically-modified animals, such as knockout mice.