Improved production and expanded application of CVS-N2c-ΔG virus for retrograde tracing

Neurotropic virus tracers, particularly those with low toxicity and high efficient tracing, are powerful tools for structural and functional dissections of neural circuits. The retrograde trans-mono-synaptic technology based on rabies virus CVS-N2c strain has reduced cytotoxicity and enhanced efficiency, attains long-term gene manipulation for functional studies, but suffers from difficult preparation and low yield. To overcome these shortcomings, an improved production system was established for rapid rescue and preparation of CVS-N2c-{Delta}G virus, CVS-N2c-{Delta}G with the same titer as SAD-B19-{Delta}G can be prepared within a short time. Meanwhile, we found that N2cG coated CVS-N2c-{Delta}G allows efficient retrograde access to projection neurons, and further expand its application in VTA/SNc to DLS pathway that unaddressed by rAAV9-Retro, and the efficiency is 6 folds higher than that of rAAV9-Retro. Then the trans-synaptic efficiency of CVS-N2c-{Delta}G virus was evaluated. Results showed that the trans-mono-synaptic efficiency of oG-mediated CVS-N2c-{Delta}G was 2-3 folds higher than that of oG-mediated SAD-B19-{Delta}G, but there was no difference between oG-mediated and N2cG-mediated CVS-N2c-{Delta}G system. In addition, codon modified N2cG (optiG) did not increase the efficiency of CVS-N2c-{Delta}G tracing. Finally, we found that the CVS-N2c-{Delta}G produced by the improved method can be used for monitoring neural activity of projection neurons, and the time window can be maintained for 3 weeks, and it can also express sufficient recombinases for efficient transgene recombination. That is, the virus produced by the improved production system does not affect its own function, paving the way for its further optimization, popularization and application in structural and functional studies of neural circuits.