Fig. 1.

Schematic of the genome structure and flowchart for the preparation of viral tracers. A Schema of the genome structure of the H129-derived tracers. P_CMV, CMV promoter; 2×GFP, GFP-2A-GFP expression cassette; tdT, tdTomato coding gene; Zeo^R, zeocin-resistant gene; dTK, deleted viral TK gene (replaced by Zeo^R). B Flowchart of the preparation of H129-derived tracers. C Schema of the genome structure of AAVs as helpers for H129-derived monosynaptic tracers. AAV-TK-GFP and AAV-DIO-TK-GFP (Cre-dependent) are helper viruses for anterograde monosynaptic tracing from starter cells. D Brief flowchart of the preparation of helper AAVs.