# Development of Cre-dependent retrograde trans-multisynaptic tracer based on pseudorabies virus bartha strain

## TL;DR

Researchers developed new tools to trace neural circuits using a modified virus that can track connections in the brain.

## Contribution

The study introduces two Cre-dependent retrograde trans-multisynaptic tracers based on the PRV Bartha strain.

## Key findings

- PRV676 and PRV829 can express fluorescent proteins Cre-dependently.
- The tracers can produce progeny viruses in vitro and in vivo.
- These tools help map multilevel inputs of specific neuronal subpopulations.

## Abstract

Mapping the neural circuit of a specific neuronal subclass is central to understanding the working mechanism of the brain. Currently, numerous types of transgenic mice expressing Cre recombinase have been engineered and widely used in neuroscience. To map the multilevel inputs into the neural circuit of a specific neuronal subpopulation, a Cre-dependent retrograde trans-multisynaptic tracer must be developed. The vaccine strain of Pseudorabies virus (PRV, Bartha strain) can infect neurons and spread in a retrograde manner in the neural circuit. In this study, we engineered the genome of PRV Bartha strain to prepare two new tracers, PRV676 and PRV829, by replacing the TK gene of PRV with the Cre-dependent expression cassette of the fluorescent protein gene and the TK gene. These two tracers can separately and Cre-dependently express EGFP and mRuby3 and produce progeny viruses in vitro and in vivo, which can help to map the multilevel inputs of a specific neuronal subpopulation expressing Cre. Collectively, our work provides two new tools for neuroscience research.

The online version contains supplementary material available at 10.1186/s13041-025-01204-y.