Defining functional gene‐circuit interfaces in the mouse nervous system

• Published in: Genes, brain and behavior Vol. 13; no. 1; pp. 2 - 12
• Main Authors: Soden, M. E., Gore, B. B., Zweifel, L. S.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-01-2014; John Wiley & Sons, Inc
• Subjects: Adeno-associated virus; Animals; Brain - physiology; Canine adenovirus; circuits; combinatorial; conditional; Connectome - methods; Cre; Gene expression; genes; Genetic Association Studies; genetics; Genome; Mice; molecular; Nerve Net - physiology; nervous system; Neural networks; genetics; nervous system; conditional; genes; Cre; Canine adenovirus; combinatorial; molecular; mice; circuits
• ISSN: 1601-1848; 1601-183X
• DOI: 10.1111/gbb.12082

Complexity in the nervous system is established by developmental genetic programs, maintained by differential genetic profiles and sculpted by experiential and environmental influence over gene expression. Determining how specific genes define neuronal phenotypes, shape circuit connectivity and regulate circuit function is essential for understanding how the brain processes information, directs behavior and adapts to changing environments. Mouse genetics has contributed greatly to current percepts of gene‐circuit interfaces in behavior, but considerable work remains. Large‐scale initiatives to map gene expression and connectivity in the brain, together with advanced techniques in molecular genetics, now allow detailed exploration of the genetic basis of nervous system function at the level of specific circuit connections. In this review, we highlight several key advances for defining the function of specific genes within a neural network.
Combinatorial viral and genetic approaches to studying gene necessity and sufficiency in the mouse brain. Projection‐specific genetic necessity can be tested using viral delivery of shRNA or a dominant‐negative (DN) version of the gene of interest (a). In this example, the retrograde transducing viral vector (CAV) containing a Cre expression cassette is injected into a target area of interest and a local transducing virus (AAV) containing either a conditional shRNA to the gene of interest or a conditional expression cassette for a DN protein is injected into the area of interest (gray). Intersectional neurons projecting to the target (purple) will express the shRNA or DN and other projection neurons (gray) will be unaffected. Genetic sufficiency can be tested in a brain nucleus of interest on a null allele background by injecting a locally transducing viral vector (b) containing a rescue cassette (AAV‐Rescue), but this will be expressed in all neurons within the region injected (green). Alternatively, cell‐selective gene sufficiency testing can be performed if the null allele is generated by insertion of Cre into the gene's open reading frame (c). Injection of a conditional rescue cassette (AAV‐FLEX‐Rescue) into a nucleus of interest restores gene expression only to the neurons endogenously expressing the gene (green). A caveat to this approach is that it will restore expression of the gene to cells projecting to multiple targets. A combined viral vector approach for testing gene sufficiency in neurons projecting to a specific target can also be performed, similar to necessity testing in (a). Here, CAV‐Cre is injected into a target of interest and the conditional AAV‐FLEX‐Rescue virus is injected into the area of interest to express the transgene only in a specific projecting population (d).