Ben-Simon, Y.; Hooper, M.; Narayan, S.; Daigle, T.; Dwivedi, D.; Way, S. W.; Oster, A.; Stafford, D. A.; Mich, J. K.; Taormina, M. J.; Martinez, R. A.; Opitz-Araya, X.; Roth, J. R.; Allen, S.; Ayala, A.; Bakken, T. E.; Barcelli, T.; Barta, S.; Bendrick, J.; Bertagnolli, D.; Bowlus, J.; Boyer, G.; Brouner, K.; Casian, B.; Casper, T.; Chakka, A. B.; Chakrabarty, R.; Chance, R. K.; Chavan, S.; Departee, M.; Donadio, N.; Dotson, N.; Egdorf, T.; Gabitto, M.; Gary, A.; Gasperini, M.; Goldy, J.; Gore, B. B.; Graybuck, L.; Greisman, N.; Haeseleer, F.; Halterman, C.; Helback, O.; Hockmeyer, D.; Huang,

The mammalian cortex is comprised of cells with different morphological, physiological, and molecular properties that can be classified according to shared properties into cell types. Defining the contribution of each cell type to the computational and cognitive processes that are guided by the cortex is essential for understanding its function in health and disease. We use transcriptomic and epigenomic cortical cell type taxonomies from mice and humans to define marker genes and enhancers, and to build genetic tools for cortical cell types. Here, we present a large toolkit for selective targeting of cortical populations, including mouse transgenic lines and recombinant adeno-associated virus (AAV) vectors containing genomic enhancers. We report evaluation of tens of new transgenic lines and of >680 different enhancer AAVs covering all major subclasses of cortical cells, with many achieving a high degree of specificity, comparable with existing transgenic lines. We find that the transgenic lines based on marker genes can provide exceptional specificity and completeness of cell type labeling, but frequently require generation of a triple-transgenic cross for best usability/specificity. On the other hand, enhancer AAVs are easy to screen and use, and can be easily modified to express diverse cargo, such as recombinases. However, their use depends on the titer and delivery method. The tools reported here as well as the scaled process of tool creation provide an unprecedented resource that should enable diverse experimental strategies towards understanding mammalian cortex and brain function.