Rescue and Characterization of Recombinant Virus from a New World Zika Virus Infectious Clone

Summary

This protocol describes the recovery of infectious Zika virus from a two-plasmid infectious cDNA clone.

Abstract

Infectious cDNA clones allow for genetic manipulation of a virus, thus facilitating work on vaccines, pathogenesis, replication, transmission and viral evolution. Here we describe the construction of an infectious clone for Zika virus (ZIKV), which is currently causing an explosive outbreak in the Americas. To prevent toxicity to bacteria that is commonly observed with flavivirus-derived plasmids, we generated a two-plasmid system which separates the genome at the NS1 gene and is more stable than full-length constructs that could not be successfully recovered without mutations. After digestion and ligation to join the two fragments, full-length viral RNA can be generated by in vitro transcription with T7 RNA polymerase. Following electroporation of transcribed RNA into cells, virus was recovered that exhibited similar in vitro growth kinetics and in vivo virulence and infection phenotypes in mice and mosquitoes, respectively.

Introduction

Zika virus (ZIKV; Family Flaviviridae: Genus Flavivirus) is a mosquito-borne flavivirus that arrived in Brazil in 2013-14 and was subsequently associated with a massive outbreak of febrile illness that spread throughout the Americas¹. In addition, ZIKV has been linked with severe disease outcomes, such as Guillain-Barré syndrome in adults and microcephaly in fetuses and neonates². Little was known about ZIKV before its rapid spread in the western hemisphere. This included a lack of molecular tools, thus hindering mechanistic research. Molecular tools for viruses, such as infectious cDNA clones, fac....

Protocol

1. Transform and Recovery of Infectious Clone Plasmids

1. Transform both plasmids (separately) using a commercial transformation protocol (e.g., NEB 5 Minute Transformation Protocol) with some modifications. Both plasmids contain a gene encoding for ampicillin resistance, therefore use ampicillin or carbenicillin for selection. Carbenicillin is preferred, as it is more stable.
   1. Remove cells (See Materials Table) from -80 °C freezer and thaw on ice for 5-10 min. Prewarm lysogeny broth (LB) (containing 10 g/L NaCl and 25 µg/mL carbenicillin; called LB-carb) plates and the broth with catabolite repression (SOC (with....

Results

The protocol described here allows for the recovery of infectious clone-derived Zika virus. Manipulating the two-plasmid infectious clone system is straightforward when performed with care, as compared to full-length versions which are highly unstable (data not shown). After digestion and ligation of the two distinct pieces, capped RNA is produced using in vitro transcription with T7 polymerase which is then electroporated into Vero cells (Figure 1)........

Discussion

Here we describe a method for the recovery of a bipartite infectious cDNA clone system for ZIKV. Previously described clones for ZIKV suffer from either attenuation or require the addition of introns, making plasmids larger and preventing rescue in insect cells. Infectious virus can be recovered using the two-plasmid clone system in either mammalian or insect cells (data not shown). In addition, virus recovered from this system behaves similarly to wild-type virus in several cell lines, in an immunocompromised mouse mode.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
NEB Stable CompetentE. coli	New England BioLabs	C3040H
Carbenicillin, Disodium Salt	various
Zyppy Plasmid Miniprep Kit	Zymo Research	D4036
ZymoPURE Plasmid Maxiprep Kit	Zymo Research	D4202
SalI-HF	New England BioLabs	R3138S	20,000 units/ml
NheI-HF	New England BioLabs	R3131S	20,000 units/ml
ApaLI	New England BioLabs	R0507S	10,000 units/ml
EcoRI-HF	New England BioLabs	R3101S	20,000 units/ml
BamHI-HF	New England BioLabs	R3136S	20,000 units/ml
HindIII-HF	New England BioLabs	R3104S	20,000 units/ml
illustra TempliPhi 100 Amplification Kit	GE Healthcare Life Sciences	25640010
NucleoSpin Gel and PCR Clean-up	Macherey-Nagel	740609.5
Shrimp Alkaline Phosphatase (rSAP)	New England BioLabs	M0371S	1,000 units/ml
Alkaline Phosphatase, Calf Intestinal (CIP)	New England BioLabs	M0290S	10,000 units/ml
T4 DNA Ligase	New England BioLabs	M0202S	400,000units/mL
HiScribe T7 ARCA mRNA Kit	New England BioLabs	E2065S
Vero cells	ATCC	CCL-81
ECM 630 High Throughput Electroporation System	BTX	45-0423	Other machines are acceptable.
LB Broth with agar (Miller)	Sigma	L3147	Can be homemade as well.
Terrific Broth	Sigma	T0918	Can be homemade as well.
Petri Dish	Celltreat	229693
Culture Tubes	VWR International	60818-576
T75 flasks	Celltreat	229340
T182 flasks	Celltreat	229350
1x PBS	Corning	21-040-CV
RPMI 1640 with L-glutamine	Corning	10-040-CV
DMEM with L-glutamine and 4.5 g/L glucose	Corning	10-017-CV
Fetal Bovine Serum (FBS)	Atlas Biologicals	FP-0500-A
Tragacanth Powder	MP Bio	MP 104792
Crystal Violet	Amresco	0528-1006
Ethanol Denatured	VWR International	BDH1156-1LP
6 well plate	Celltreat	229106
12 well plate	Celltreat	229111
Sequencing Oligos	IDT	see table 1
Qubit 3.0	ThermoFisher	Qubit 3.0	other methods are acceptable.
Qubit dsDNA BR Assay Kit	ThermoFisher	Q32850	other methods are acceptable.
Qubit RNA HS Assay Kit	ThermoFisher	Q32852	other methods are acceptable.
Class II Biosafety Cabinet	Varies	N/A	This is necessary for live-virus work.