Specificity and efficiency of reporter expression in adult neural progenitors vary substantially among nestin-CreER^T2 lines

Transgenic lines expressing a controllable form of Cre recombinase have become valuable tools for manipulating gene expression in adult neural progenitors and their progeny. Neural progenitors express several proteins that distinguish them from mature neurons, and the promoters for these genes have been co-opted to produce selective transgene expression within this population. To date, nine CreER^T2 transgenic lines have been designed using the nestin promoter; however, only a subset are capable of eliciting expression within both neurogenic zones of the adult brain. Here we compare three such nestin-CreER^T2 lines to evaluate specificity of expression and efficiency of recombination. Each line was examined by using three different Cre reporter strains that varied in sensitivity. We found that all three nestin-CreER^T2 strains induced reporter expression within the main neurogenic areas, albeit to varying degrees depending on the reporter. Unexpectedly, we found that two of the three lines induced substantial reporter expression outside of neurogenic areas. These lines produced strong labeling in cerebellar granule neurons, with additional expression in the cortex, hippocampus, striatum, and thalamus. Reporter expression in the third nestin-CreER^T2 line was considerably more specific, but was also less efficient, labeling a smaller percentage of the target population than the other two drivers. Our findings suggest that each nestin-CreER^T2 line may best serve different experimental needs, depending on whether specificity or efficiency is of greatest concern. Our study further demonstrates that each new pair of driver and responder lines should be evaluated independently, as both components can significantly influence the resulting expression pattern.