Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2016 Apr 19;5(4):e306.
doi: 10.1038/mtna.2016.21.

pEVL: A Linear Plasmid for Generating mRNA IVT Templates With Extended Encoded Poly(A) Sequences

Alexandra E Grier  1   2   3 , Stephen Burleigh  1 , Jaya Sahni  1 , Courtnee A Clough  1 , Victoire Cardot  1 , Dongwook C Choe  1 , Michelle C Krutein  4 , David J Rawlings  1   3   5 , Michael C Jensen  2   5   6   7 , Andrew M Scharenberg  1   3   5 , Kyle Jacoby  1
Affiliations

pEVL: A Linear Plasmid for Generating mRNA IVT Templates With Extended Encoded Poly(A) Sequences

Alexandra E Grier et al. Mol Ther Nucleic Acids. .

Abstract

Increasing demand for large-scale synthesis of in vitro transcribed (IVT) mRNA is being driven by the increasing use of mRNA for transient gene expression in cell engineering and therapeutic applications. An important determinant of IVT mRNA potency is the 3' polyadenosine (poly(A)) tail, the length of which correlates with translational efficiency. However, present methods for generation of IVT mRNA rely on templates derived from circular plasmids or PCR products, in which homopolymeric tracts are unstable, thus limiting encoded poly(A) tail lengths to ~120 base pairs (bp). Here, we have developed a novel method for generation of extended poly(A) tracts using a previously described linear plasmid system, pJazz. We find that linear plasmids can successfully propagate poly(A) tracts up to ~500 bp in length for IVT mRNA production. We then modified pJazz by removing extraneous restriction sites, adding a T7 promoter sequence upstream from an extended multiple cloning site, and adding a unique type-IIS restriction site downstream from the encoded poly(A) tract to facilitate generation of IVT mRNA with precisely defined encoded poly(A) tracts and 3' termini. The resulting plasmid, designated pEVL, can be used to generate IVT mRNA with consistent defined lengths and terminal residue(s).

PubMed Disclaimer

Figures

Figure 1
Figure 1
Shortening of poly(A) tracts upon cloning into standard circular plasmid cloning vector at 25 °C. BFP-poly(A) tract inserts of 70, 172, and 325 base pairs bounded by restriction enzyme sites DraIII and SwaI were generated via restriction enzyme digest from the linear plasmid cloning vectors BFP-pEVL-100, BFP-pEVL-200, and BFP-pEVL-300 (described in subsequent portions of the manuscript). The inserts were ligated into a circular cloning vector, designated pWNY, and the resulting plasmids were transformed into Escherichia coli using standard methods and grown at 25 °C. Individual colonies were amplified by PCR using primers flanking the poly(A) tract, and the length of the poly(A) tract was estimated based on the resulting band size. Typically, a band was obtained either near the expected size, or at a smaller size, reflecting shortening of the poly(A) tract during transformation. Colonies were scored for whether the poly(A) tract fragment was approximately of the expected size (open circle), or was substantially shortened (closed circle). BFP, blue fluorescent protein; pEVL, p(Extended Variable Length); poly(A), polyadenosine.
Figure 2
Figure 2
Generation of pEVL: a linear plasmid vector for generation of mRNA with extended encoded poly(A) tracts. (a) Schematic of pJazz and conversion to pEVL. The plasmids are shown with orange arrows denoting genes, red circles with T's denoting transcriptional terminators, open circles denoting terminal hairpin loops, yellow blocks denoting BsaI sites, and green blocks denoting the poly(A) tail. (b) Schematic of pEVL and method used for generation of extended poly(A) tracts in pEVL.
Figure 3
Figure 3
Characterization of poly(A) tract stability in pEVL. (a) Stability of the encoded poly(A) tracts following overnight induction of pEVL for template preparation. BFP-pEVL-200 through 500 were grown overnight with induction at 30 °C and then maxiprepped. Each maxiprepped sample was digested with BsiWI and BsaI to release the poly(A) tail fragment from the rest of the plasmid. The tail length was determined by gel electrophoresis with comparison to a known molecular weight standard. (b) Shortening of poly(A) tracts upon cloning into standard circular or linear plasmid cloning vectors at 30 °C. BFP followed by poly(A) tract inserts of 70, 172, and 325 base pairs bounded by restriction enzyme sites DraIII and SwaI were generated via restriction enzyme digest from the linear plasmid cloning vectors pEVL-100, pEVL-200, and pEVL-300. The inserts were ligated into the circular cloning vector pWNY or subcloned into pEVL and transformed via electroporation. Transformed bacteria were grown with ampicillin (pWNY) or kanamycin (pEVL) selection at 30 °C. Individual colonies were amplified by PCR using primers flanking the poly(A) tract, and the length of the poly(A) tract was determined based on the resulting band size as in Figure 1. Typically, a band was obtained at the expected size, or a smaller size, reflecting shortening of the poly(A) tract during transformation. Colonies were scored for whether the poly(A) tract fragment was approximately of the expected size (open circle), or was substantially shortened (closed circle). (c) Stability of encoded poly(A) tracts under extended propagation conditions. To test the stability of the poly(A) tail under stringent propagation conditions, pEVL 100 through 500 were grown for 2 weeks at 30 °C and 37 °C with reseeding into fresh media at a 1:1000 dilution every 24 hours. At days 0, 6, and 13, each sample was similarly reseeded into induction media and grown overnight before being miniprepped. Parallel analysis was performed with the circular vectors described in (b), in which the poly(A) tract fragment was sub-cloned into a circular vector (pWNY). As these are already high-copy plasmids, no inducing agent was added to the cultures. For the circular vectors, samples were miniprepped daily for 7 days. For both pEVL and the circular vectors, the tail length of the induced minipreps was determined by gel elctrophoresis as described above. The expected tail band size for each construct is indicated with an arrow.
Figure 4
Figure 4
Generation and characterization of mRNA from pEVL-encoded templates. (a) IVT mRNA encoding blue fluorescent protein (mTagBFP2) generated from pWNY with enzymatic tailing and pEVL-100 through pEVL-500. BFP-pEVL-100 to 500 were digested with XbaI and BsaI, and pWNY with ScaI and BsiWI, to generate template for IVT. IVT was carried out with antireverse cap analog capping, and for pWNY, enzymatic tailing with EPAP. After purification, 200 ng of each transcript was imaged via gel electrophoresis on the FlashGel system. Typically, pEVL produces a single band of defined length, whereas pWNY with enzymatic tailing produces transcripts of a more heterogenous length. (b) Relative potency of mRNA encoding BFP generated from a circular plasmid vector with enzymatic polyadenylation or from pEVL-300 and representative flow plots. 1 μg of IVT mRNA from the indicated template was electroporated into prestimulated primary human T cells. After a 24-hour cold shock at 30 °C, the cells were analyzed each day for 5 days by flow cytometry for the percentage of cells expressing BFP as well as the mean fluorescence intensity (MFI) of the BFP in BFP+ cells. Flow plots are shown as side scatter (SSC) versus BFP. (c) Relative potency of mRNA encoding BFP generated from pEVL-100 through pEVL-500 and representative flow plots. Equimolar amounts of IVT mRNA from BFP-pEVL-100 to 500 were electroporated into prestimulated primary human T cells. After an initial 24-hour cold shock at 30 °C, the cells were grown at 37 °C for 6 more days. Every 24 hours after electroporation, the percentage of cells expressing BFP and the BFI MFI of the BFP+ cells was analyzed by flow cytometry. Flow plots are shown as side scatter (SSC) versus BFP. BFP, blue fluorescent protein; IVT, in vitro transcribed; pEVL, p(Extended Variable Length).
Figure 5
Figure 5
Application of pEVL-encoded mRNA for gene editing in primary human T cells. (a) pEVL-mediated editing of the TCRα locus with TALEN mRNAs in primary human T cells. TALENs targeting the constant region of the TCRα locus were each cloned into pEVL-300. After IVT mRNA production, the indicated amounts of mRNA encoding each TALEN half were electroporated into prestimulated primary human T cells. In the left panel, cells were incubated at 37 °C immediately following electroporation. In the right panel, cells were incubated at 30 °C for 24 hours to increase nuclease protein accumulation after electroporation and then moved to 37 °C. At 72 hours postelectroporation, successful TCR knockout was assayed by flow cytometry for a loss of CD3 expression. (b) pEVL-mediated editing of the TCRα locus with CRISPR/Cas9 in primary human T cells. A Cas9-T2A-mCherry construct was cloned into pEVL-200. After IVT mRNA production, Cas9 was electroporated into prestimulated primary human CD4+ T cells. 3 hours postelectroporation, a CRISPR guide targeting the TCRα constant region was delivered via AAV6 transduction. After electroporation, the cells were incubated at 30 °C for 24 hours before being moved to 37 °C. At 24 and 72 hours postelectroporation, Cas9 electroporation efficiency was determined by FACS analysis of mCherry fluorescence. After 7 days, successful TCR knockout was assayed by flow cytometry for a loss of CD3 expression. (c) Representative RNA FlashGels showing the mRNA transcripts for the left half and right half of the TCRα TALENS produced via enzymatic tailing and from pEVL-300. (d) Representative RNA FlashGels showing the mRNA transcripts for Cas9-T2A-mCherry produced via enzymatic tailing and from pEVL-200. AAV6, adeno-associated vector 6; IVT, in vitro transcribed; pEVL, p(Extended Variable Length).
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Morgan, RA and Kakarla, S (2014). Genetic modification of T cells. Cancer J 20: 145–150. - PubMed
    1. Zhao, Y, Zheng, Z, Cohen, CJ, Gattinoni, L, Palmer, DC, Restifo, NP et al. (2006). High-efficiency transfection of primary human and mouse T lymphocytes using RNA electroporation. Mol Ther 13: 151–159. - PMC - PubMed
    1. Knudsen, ML, Ljungberg, K, Liljeström, P and Johansson, DX (2014). Intradermal electroporation of RNA. Methods Mol Biol 1121: 147–154. - PubMed
    1. Smits, E, Ponsaerts, P, Lenjou, M, Nijs, G, Van Bockstaele, DR, Berneman, ZN et al. (2004). RNA-based gene transfer for adult stem cells and T cells. Leukemia 18: 1898–1902. - PubMed
    1. Holtkamp, S, Kreiter, S, Selmi, A, Simon, P, Koslowski, M, Huber, C et al. (2006). Modification of antigen-encoding RNA increases stability, translational efficacy, and T-cell stimulatory capacity of dendritic cells. Blood 108: 4009–4017. - PubMed