Development of a rabies virus-based retrograde tracer with high trans-monosynaptic efficiency by reshuffling glycoprotein

Fan Jia,Chen Ling,Yang Wu,Haizhou Liu,Xiangwei Shi,Fuqiang Xu,Pei Lv,Li Li

doi:10.1186/s13041-021-00821-7

Abstract

Rabies virus (RV) is the most widely used vector for mapping neural circuits. Previous studies have shown that the RV glycoprotein can be a target to improve the retrograde transsynaptic tracing efficiency. However, the current versions still label only a small portion of all presynaptic neurons. Here, we reshuffled the oG sequence, a chimeric glycoprotein, with positive codon pair bias score (CPBS) based on bioinformatic analysis of mouse codon pair bias, generating ooG, a further optimized glycoprotein. Our experimental data reveal that the ooG has a higher expression level than the oG in vivo, which significantly increases the tracing efficiency by up to 12.6 and 62.1-fold compared to oG and B19G, respectively. The new tool can be used for labeling neural circuits Therefore, the approach reported here provides a convenient, efficient and universal strategy to improve protein expression for various application scenarios such as trans-synaptic tracing efficiency, cell engineering, and vaccine and oncolytic virus designs.

Highlights

Mapping neural circuits is a prerequisite to elucidate the mechanisms of brain functions
Canine is one of the Rabies virus (RV) reservoir hosts, which providing the opportunity that RV has adopted the Codon pair bias (CPB) of canine during the long-term co-evolution
We found that the majority of genes in mouse and canine have positive codon pair bias score (CPBS), averaged at 0.0651 and 0.0704, respectively, which are similar to the human 0.0703 (Additional file 1: Fig. S1)

Summary

Introduction

Mapping neural circuits is a prerequisite to elucidate the mechanisms of brain functions. Several neurotropic viruses can infect neurons and spread across synapses between neurons, playing important roles in depicting the neurocircuit [1]. Among these virus-based tools, rabies virus (RV), encoding five proteins (N, P, M, G and L), is the most popular trans-monosynaptic viral tool to map the direct input networks of specific types of neurons in specific brain regions [2,3,4,5,6]. When AAV-G infects neurons, the G expression cassette cannot be replicated because of the AAV features (or the template number for G-gene is fixed), while EnvA-RV-delG enters the same neuron, the G-deleted RV genome can be reproduced and expressed according to the RV life cycle

Methods

Results

Conclusion