Dissecting mammalian cortical circuit development at single-cell resolution using inducible barcoded rabies virus

Traditional monosynaptic rabies virus (RV) tracing is a powerful tool for mapping neural connections, yet it is severely limited by cytotoxicity. Because the virus rapidly kills the neurons it infects, researchers are often restricted to short observation windows and are unable to study the long-term maturation of developing neural circuits. To solve this, the researchers engineered an inducible barcoded rabies virus (ibRV) by fusing destabilizing domains to core viral proteins (N, P, and L). This system allows researchers to keep the virus in a dormant state and then trigger replication on demand using the drug trimethoprim (TMP).

By controlling the timing of viral replication, the authors successfully labeled neuronal circuits across multiple developmental stages in mice, from late embryonic (E16.5) to early postnatal development. This approach significantly increased neuronal survival compared to conventional rabies strains. The team demonstrated that their inducible system maintains efficient transsynaptic spread while avoiding the rapid cellular degradation typically associated with rabies infection. By performing in utero injections, they were able to achieve near whole-brain labeling, providing a new way to observe how synaptic networks assemble and mature over time.

Beyond just mapping connections, the study combined ibRV with spatial transcriptomics (Open-ST) to link neuronal wiring to specific molecular identities. By mapping rabies-encoded barcodes onto spatially resolved transcriptomic data, the researchers successfully reconstructed cell-type-specific wiring diagrams. This methodology provides a high-resolution view of how specific cortical and thalamocortical circuits refine their connectivity during early brain development. This combined framework allows scientists to move past static snapshots and begin investigating how developmental processes, and eventually neurodevelopmental disorders, reshape brain architecture.